{"id":8726,"date":"2023-11-04T20:24:03","date_gmt":"2023-11-04T14:54:03","guid":{"rendered":"https:\/\/apboardsolutions.guru\/?p=8726"},"modified":"2023-11-10T16:47:44","modified_gmt":"2023-11-10T11:17:44","slug":"ap-board-9th-class-physical-science-important-questions-chapter-6","status":"publish","type":"post","link":"https:\/\/apboardsolutions.guru\/ap-board-9th-class-physical-science-important-questions-chapter-6\/","title":{"rendered":"AP Board 9th Class Physical Science Important Questions Chapter 6 Chemical Reactions and Equations"},"content":{"rendered":"

AP State Syllabus AP Board 9th Class Physical Science Important Questions<\/a> Chapter 6 Chemical Reactions and Equations<\/p>\n

AP State Syllabus 9th Class Physical Science Important Questions 6th Lesson Chemical Reactions and Equations<\/h2>\n

9th Class Physical Science6th Lesson Chemical Reactions and Equations 1 Mark Important Questions and Answers<\/h3>\n

Question 1.
\nFe2<\/sub>O3<\/sub> + 2 Al \u2192 Al2<\/sub>O3<\/sub> + 2Fe
\nName the compound which is oxidized in the above reaction.
\nAnswer:
\nIn the reaction Fe2<\/sub>O3<\/sub> + 2Al \u2192 Al2<\/sub>O3<\/sub> + 2Fe,
\nAluminium (Al) is oxidised and formed as Al2<\/sub>O3<\/sub>.<\/p>\n

Question 2.
\nGive an example for displacement reaction.
\nAnswer:
\n1) In displacement reaction one element displaces another element from its compound and takes its place there in.<\/p>\n

2) Eg : Zinc pieces react with dilute hydrochloric acid and liberate Hydrogen gas.
\nZn(s)<\/sub>+ 2HCl(aq)<\/sub> \u2192 ZnCl2(aq)<\/sub> + H2(g)<\/sub><\/p>\n

\"AP<\/p>\n

Question 3.
\nA shiny brown coloured element ‘X’ on heating in air becomes black in colour. Assume and write the name of the element ‘X’ and also predict the substance formed black in colour.
\nAnswer:
\nElement X – Copper.
\nBlack substance – Copper Oxide<\/p>\n

Question 4.
\nIron gets rust but Gold doesn’t, why?
\nAnswer:
\nGold does not oxidized.
\n(OR)
\nGold is least reactive metal.<\/p>\n

Question 5.
\nWhat happens if iron articles are exposed to moist air? Write the chemical equation to represent that reaction.
\nAnswer:
\nRusting takes place on iron articles when they are exposed to moist air.
\n2Fe(s)<\/sub> + O2(g)<\/sub> + 4H+<\/sup>(aq)<\/sub> \u2192 2Fe2+<\/sup>(aq)<\/sub> + 2H2<\/sub>O(l)<\/sub><\/p>\n

Question 6.
\nOn adding dilute hydrochloric acid to copper oxide powder, the solution formed is blue green. Write the new compound formed.
\nAnswer:
\nCopper oxide reacts with hydrochloric acid and forms copper chloride and water. Copper chloride is in blue green colour.
\nCuO + 2 HCl \u2192 CuCl2<\/sub> + H2<\/sub>O<\/p>\n

Question 7.
\nWrite the equation for the chemical decomposition reaction of silver chloride in the presence of sunlight.
\nAnswer:
\n\"AP<\/p>\n

Question 8.
\nBalance the following chemical equation.
\nNa + H2<\/sub>O \u2192 NaOH + H2<\/sub>
\nAnswer:
\n2Na + 2H2<\/sub>O \u2192 2NaOH + H2<\/sub><\/p>\n

\"AP<\/p>\n

Question 9.
\nIf you keep an iron piece in solid state CuSO4<\/sub> crystals, does it get any reaction? Guess the reason.
\nAnswer:
\nReaction will not takes place if an iron piece is placed in solid state CuSO4<\/sub> crystals because there will not exist separate Cu+2<\/sup>, SO4<\/sub>-2<\/sup> ions in CuSO4<\/sub> Crystals. In aqueous solution, they exists. So iron can not displace copper.<\/p>\n

Question 10.
\nWhat is a chemical equation?
\nAnswer:
\nChemical Equation :
\nDescribing a chemical reaction using least possible words or symbols is called a chemical equation.
\nEx : CaO + H2<\/sub>O \u2192 Ca(OH)2<\/sub><\/p>\n

Question 11.
\nWhat are “Reactants” and “Products”?
\nAnswer:
\n1) Reactants :
\nThe substances which undergo chemical change in the reaction are called ‘Reactants’.<\/p>\n

2) Products:
\nThe new substances formed in a chemical reaction are called ‘Products’.
\nEx : Zn + 2HCl \u2192 ZnCl2<\/sub> + H2<\/sub> \u2191
\n3) In above reaction Zn and 2HCl are called reactants, ZnCl2<\/sub> and H2<\/sub> are called products.<\/p>\n

Question 12.
\nWhat is a balanced chemical equation?
\nAnswer:
\nBalanced Chemical Equation :
\nA chemical reaction in which the number of atoms of different elements on the reactants side (left side) are same as those on product side (right side) is called a balanced chemical equation.
\nEx : Mg + O2<\/sub> \u2192 MgO (Unbalanced chemical equation)
\n2 Mg + O2<\/sub> \u2192 MgO (Balanced chemical equation)<\/p>\n

Question 13.
\nWhat is chemical change?
\nAnswer:
\nChemical Change :
\nThe process in which the change is affecting the identity of a molecule by a change in chemical composition is called a “chemical change”.<\/p>\n

Question 14.
\nWhat is physical change?
\nAnswer:
\nPhysical Change: The process where a change is occurring only in physical properties, without affecting the identity of the molecules is called a “physical change”.<\/p>\n

Question 15.
\nWhat is the meaning of “Exo”, “Endo” and “Thermo”?
\nAnswer:
\nThe term ‘Exo’ means outside, ‘Endo’ means inside and ‘Thermo’ means heat.<\/p>\n

\"AP<\/p>\n

Question 16.
\nWhat is oxidation? Give examples.
\nAnswer:
\nOxidation is a reaction that involves the addition of oxygen or loss of hydrogen or electrons.
\n\"AP<\/p>\n

Question 17.
\nWhat is a reduction? Give examples.
\nAnswer:
\nThe process in which a substance loses oxygen or gains hydrogen or electrons is known as reduction.
\n\"AP<\/p>\n

Question 18.
\nWhat is corrosion?
\nAnswer:
\nCorrosion :
\nWhen some metals are exposed to moisture, acids etc. they tarnish due to the formation of respective metal oxide on their surface. This process is called “corrosion”.
\n\"AP<\/p>\n

Question 19.
\nWhat is “galvanizing”?
\nAnswer:
\nIt is a method of protecting iron from rusting by coating them a thin layer of zinc.<\/p>\n

Question 20.
\nWhat is combustion?
\nAnswer:
\nThe process of burning a substance in the presence of oxygen is called “combustion”.<\/p>\n

Question 21.
\nWhat do you mean by “rancidity”?
\nAnswer:
\nFood materials containing fat \/ oil are exposed to air, for a long time they react with atmospheric oxygen and it is responsible for spoiling of food. This process is called “rancidity”.<\/p>\n

Question 22.
\nHow do you know that respiration is an exothermic reaction?
\nAnswer:
\nDuring the respiration reaction energy releases, so it is an exothermic reaction.<\/p>\n

Question 23.
\nWhat will happen in chemical reaction?
\nAnswer:
\nNew substances are formed in chemical reaction.<\/p>\n

\"AP<\/p>\n

Question 24.
\nWhat is precipitate?
\nAnswer:
\nA precipitate is a solid product’ which separates out from the solution during a chemical reaction.<\/p>\n

Question 25.
\nHow does precipitation reaction occur? Explain with an example.
\nAnswer:<\/p>\n

    \n
  1. Prepare lead nitrate and potassium iodide solutions in separate test tubes.<\/li>\n
  2. Mix the two solutions.<\/li>\n
  3. A yellow colour substance which is insoluble in water, is formed. This insoluble substance is known as precipitate. The precipitate here in this reaction is lead iodide.
    \nPb(NO3<\/sub>)2<\/sub> + 2KI \u2192 Pbl2<\/sub> + 2KNO3<\/sub><\/li>\n<\/ol>\n

    Question 26.
    \nWhat is a balanced chemical equation?
    \nAnswer:
    \nA balanced chemical equation has an equal number of atoms of different elements in the reactants and products.<\/p>\n

    Question 27.
    \nWhat is an unbalanced equation?
    \nAnswer:
    \nAn unbalanced chemical equation has an unequal number of atoms of one or more elements in the reactants and products.<\/p>\n

    Question 28.
    \nWhy do the smell and taste of food items change?
    \nAnswer:
    \nWhen fats and oils are oxidized they become rancid. So their smell and taste change.<\/p>\n

    Question 29.
    \n“Freshly cut apple turning brown, the iron articles shiny when new, but gradually become reddish brown when left for sometime ………”. How do these changes occur?
    \nAnswer:
    \nOxygen molecules interact with different substance from metal to living tissue which may come into contact with it. The above changes occur. These are all the examples of the process of oxidation.<\/p>\n

    \"AP<\/p>\n

    Question 30.
    \nWhat are antioxidants?
    \nAnswer:
    \nAntioxidants :
    \nThe spoilage of food can be prevented by adding preservatives which prevent oxidation. The substances which prevent oxidation are called antioxidants.
    \n(OR)
    \nThe substances which prevent oxidation added to food containing fats and oil are called antioxidants.<\/p>\n

    Question 31.
    \nComplete the following reaction.
    \nPb(NO3<\/sub>)2<\/sub> + 2 KI \u2192 …………….. + …………………
    \nAnswer:
    \nPb(NO3<\/sub>)2<\/sub> + 2 KI \u2192 Pbl2<\/sub> + 2KNO3<\/sub><\/p>\n

    Question 32.
    \nIf iron nail is dipped in copper sulphate solution, after sometime copper will be formed. Write the chemical equation for this reaction.
    \nAnswer:
    \nFe + CuSO4<\/sub> \u2192 FeSO4<\/sub> + Cu<\/p>\n

    Question 33.
    \nWhich metal is used in the manufacture of Diwali crackers?
    \nAnswer:
    \nThe metal used in manufacture of Diwali crackers is Magnesium.<\/p>\n

    Question 34.
    \nWhat are new substances formed due to decomposition of lead nitrate?
    \nAnswer:
    \nThe new substances formed are lead oxide, nitrogen dioxide and oxygen.<\/p>\n

    \"AP<\/p>\n

    Question 35.
    \nBalance the following chemical equation. C2<\/sub>H6<\/sub> + O2<\/sub> \u2192 CO2<\/sub> + H2<\/sub>O
    \nAnswer:
    \n2C2<\/sub>H6<\/sub> + 7O2<\/sub> \u2192 4CO2<\/sub> + 6H2<\/sub>O<\/p>\n

    Question 36.
    \nNH4<\/sub>Cl \u2192 NH3<\/sub>\u00a0+ HCl. Which type of reaction is this?
    \nAnswer:
    \nThis is decomposition reaction.<\/p>\n

    Question 37.
    \nWhich chemical reaction is involved in the corrosion of iron?
    \nAnswer:
    \nThe chemical reaction involved in corrosion of iron is oxidation reaction.<\/p>\n

    Question 38.
    \nWhich metal is used for wrapping food material? Why?
    \nAnswer:
    \nAluminium is used to wrap food material because it reacts with oxygen and forms a protective layer of aluminium oxide which prevents further oxidation.<\/p>\n

    Question 39.
    \nWrite states of the reactants and products and also write conditions required for the completion of reaction.
    \nAnswer:
    \n2H2<\/sub>O \u2192 2H2<\/sub> + O2<\/sub>
    \nH2<\/sub>O is in liquid state. H2<\/sub> and 02<\/sub> are in gaseous state.
    \nThe reaction is carried out in the presence of electricity.<\/p>\n

    Question 40.
    \nGive an example for chemical combination reaction where only elements take part.
    \nAnswer:
    \n2 H2<\/sub> + O2<\/sub> \u2192 2H2<\/sub>O
    \nHere hydrogen and oxygen both are elements.<\/p>\n

    \"AP<\/p>\n

    Question 41.
    \nGive an example for chemical combination where element and compound take part in the reaction.
    \nAnswer:
    \n2 NaN02 + O2<\/sub> \u2192 2 NaNO3<\/sub>
    \nHere O2<\/sub> is element and NaNO2<\/sub> is compound.<\/p>\n

    Question 42.
    \nGive an example where two compounds combine together to form a compound.
    \nAnswer:
    \nCaO + H2<\/sub>O \u2192 Ca(OH)2<\/sub>
    \nHere both calcium oxide, water are compounds which combine together to form calcium hydroxide.<\/p>\n

    Question 43.
    \nBefore burning in air, why is Mg ribbon cleaned by rubbing with a sand paper?
    \nAnswer:
    \nTo remove the protection layer of basic magnesium carbonate from the surface of magnesium<\/p>\n

    Question 44.
    \nX Pb(NO3<\/sub>)2<\/sub> \u2192 Y PbO + Z NO2<\/sub> + W O2<\/sub>.
    \nIf the equation is a balanced equation, what are values of coefficients X, Y, Z and W?
    \nAnswer:
    \nThe balanced equation is 2 Pb(NO3<\/sub>)2<\/sub> \u2192 2 PbO + 4 NO2<\/sub> + O2<\/sub>.
    \n\u2234 The values are X = 2,Y = 2, Z = 4 and W = 1.<\/p>\n

    Question 45.
    \nWhy does a layer of zinc prevent rusting of iron?
    \nAnswer:
    \nZinc reacts with oxygen and forms layer of zinc oxide which prevents further oxidation. So a layer of zinc protects iron from rusting.<\/p>\n

    Question 46.
    \nWhy does jewellery made of gold not rust?
    \nAnswer:
    \nGold does not react with air because it has least reactivity. So gold jewellery does not rust.<\/p>\n

    Question 47.
    \n\"AP
    \nWhat type of reaction is this? Which element between A and C is more reactive? Why?
    \nAnswer:
    \nThis reaction is chemical displacement. ‘C’ is more reactive than ‘A’. So C displaces ‘A’ from AB and occupies its place.<\/p>\n

    Question 48.
    \nGiven AB + CD \u2192 AD + CB. What type of chemical reaction is this? What is the condition which makes the reaction possible?
    \nAnswer:
    \nThis is double displacement reaction. This reaction can be possible if ionisation of both the salt solutions are possible.
    \ni.e., AB \u2192 A+<\/sup> + B–<\/sup>
    \nCD \u2192 C+<\/sup> + D–<\/sup><\/p>\n

    Question 49.
    \nAn iron nail is completely immersed in a test tube containing oil. Do you observe any rust on the iron nail? If not, why?
    \nAnswer:
    \nNo, I do not observe any rust because both air and moisture are required for rusting of iron.<\/p>\n

    \"AP<\/p>\n

    Question 50.
    \nHow can we prevent rusting of iron?
    \nAnswer:
    \nRusting of iron can be prevented or at least minimised by shielding the metal surface from oxygen and moisture. It can be prevented by painting, oiling, greasing, galvanizing, chrome plating or making alloys.<\/p>\n

    Question 51.
    \nSuggest few methods to avoid corrosion.
    \nAnswer:
    \nSome methods to avoid corrosion<\/p>\n

      \n
    1. Painting, oiling, greasing on the surfaces of the metals.<\/li>\n
    2. Galvanizing the metal with thin layer of zinc.<\/li>\n
    3. Making alloy metals prevents corrosion,
      \neg : brass, bronze and steel.<\/li>\n<\/ol>\n

      Question 52.
      \nSome metals react with oxygen to form their oxides. It is serious problem. Give some examples for oxidation of metals and write balanced equations.
      \nAnswer:
      \n1) Iron reacts with oxygen and forms iron oxide.
      \n4Fe + 3O2<\/sub> \u2192 2Fe2<\/sub>O3<\/sub>.<\/p>\n

      2) Copper reacts with oxygen and forms copper oxide.
      \n2Cu + O2<\/sub> \u2192 2CuO<\/p>\n

      3) Silver tarnishes when reacts with hydrogen sulphide and oxygen
      \n4Ag + 2H2<\/sub>S + O2<\/sub> \u2192 2Ag2<\/sub>S + 2H2<\/sub>O<\/p>\n

      Question 53.
      \nWhich pipes are suggestable\/suitable for water supply? Justify your answer.
      \nAnswer:
      \nSteel, PVC and CPVC pipes are suitable\/suggestable for water supply.
      \nReasons:<\/p>\n

        \n
      1. They are not oxidised in moisture.<\/li>\n
      2. They do not form oxides.<\/li>\n
      3. They are not corroded.<\/li>\n
      4. So, they are durable and safe to use in supply of water.<\/li>\n<\/ol>\n

        Question 54.
        \nWhich pipes are used by you for water supply to your house?
        \nAnswer:<\/p>\n

          \n
        1. PVC, CPVC and steel pipes are used for water supply in my house.<\/li>\n
        2. Because they do not corrode.<\/li>\n<\/ol>\n

          Question 55.
          \nList of metals are given below. Classify them into corroded and non-corroded metals. Aluminium, Silver, Iroh, Copper, Gold, Tin, Tungsten, Platinum.
          \nAnswer:
          \nCorroded metals :
          \nAluminium, Silver, Iron, Copper<\/p>\n

          Non-corroded metals :
          \nGold, Tin, Tungsten, Platinum.<\/p>\n

          9th Class Physical Science6th Lesson Chemical Reactions and Equations 2 Marks Important Questions and Answers<\/h3>\n

          Question 1.
          \nA light yellow coloured compound \u2018X\u2019 is exposed to sunlight for some time. It is turned into gray coloured material. What is the name of \u2018X\u2019? Predict the type of chemical reaction occured in it.
          \nAnswer:
          \n1) The name of the compound \u2018X\u2019 is Silver Bromide (AgBr).
          \n\"AP<\/p>\n

          This is a decomposition reaction and also it occurs in the presence of sunlight. Hence, it is a photo chemical reaction.<\/p>\n

          Question 2.
          \nOil and fat containing food item packets are flushed with Nitrogen gas. Why?
          \nAnswer:
          \nBy stopping the oxidation it prevents the rancidity of food material.<\/p>\n

          \"AP<\/p>\n

          Question 3.
          \nN2(g)<\/sub> + O2(g)<\/sub> + heat \u2192 2NO(g)<\/sub>
          \nWhat information do you get from the above equation? Comment.
          \nAnswer:<\/p>\n

            \n
          • Nitrogen gas reacts with oxygen gas in the presence of heat energy and forms nitric oxide gas.<\/li>\n
          • It is an endothermic reaction.<\/li>\n
          • This is an example for chemical combination reaction.<\/li>\n
          • In this reaction, the reactants are gases and products are also gases.<\/li>\n<\/ul>\n

            Question 4.
            \nWrite an activity about how you conduct an experiment to show that more reactive metals replace less reactive metals from their compounds.
            \nAnswer:<\/p>\n

              \n
            • Take two iron nails and clean then by rubbing with sand paper.<\/li>\n
            • Take two test tubes and mark them ‘A’ and ‘B’.<\/li>\n
            • Pour copper sulphate solution in the test tube ‘A’ and Zinc Chloride solution in the test tube ‘B’.<\/li>\n
            • Dip iron nails in both test tubes.<\/li>\n
            • Keep them without disturbing for 20 min.<\/li>\n<\/ul>\n

              Observation :<\/p>\n

                \n
              1. The nail which is dipped in Copper Sulphate solution becomes brownish colour.<\/li>\n
              2. The nail which is dipped in Zinc Chloride solution doesn’t change.<\/li>\n<\/ol>\n

                Reaction :
                \nIn test tube ‘A’: CuSO4<\/sub> + Fe \u2192 FeSO4<\/sub> + Cu
                \nIn test tube ‘B’: ZnCl2<\/sub> + Fe \u2192 No reaction.<\/p>\n

                Conclusion :<\/p>\n

                  \n
                1. Iron is more reactive than copper. So it displaces copper from Copper Sulphate solution.<\/li>\n
                2. Iron is less reactive than zinc. So, it doesn\u2019t displace zinc from ZnClr<\/li>\n<\/ol>\n

                  Question 5.
                  \ni) CaCO3(s)<\/sub> \u2192 CaO(s)<\/sub> + CO3(g)<\/sub>
                  \nii) 2Ag Br(s)<\/sub> \u2192 2Ag(s)<\/sub> + Br2(g)<\/sub>
                  \nMention the types of reactions to which the above equations belong. Also mention which of them is a photochemical reaction.
                  \nAnswer:
                  \n1) i) CaCO3(s)<\/sub> \u2192 CaO(s)<\/sub> + CO2(g)<\/sub>. It is a chemical decomposition reaction.
                  \nii) 2Ag Br(s)<\/sub> \u2192 2Ag(s)<\/sub> + Br2(g)<\/sub>. It is also a chemical decomposition reaction.<\/p>\n

                  2) 2Ag Br(s)<\/sub> \u2192 2Ag(s)<\/sub> + Br2(g)<\/sub>. It is a photochemical reaction. Because, this reaction
                  \ntakes place in the presence of sunlight only.<\/p>\n

                  Question 6.
                  \nWrite the products of given reactions, if any. Give reason.
                  \nFeCl2<\/sub> + Zn \u2192
                  \nZnCl2<\/sub> + Fe \u2192
                  \nAnswer:
                  \nFeCl2<\/sub> + Zn \u2192 ZnCl2<\/sub> + Fe (Displacement reaction)
                  \nZnCl2<\/sub> + Fe \u2192 No reaction. (Low reactive metals cannot displace high reactive metals)<\/p>\n

                  \"AP<\/p>\n

                  Question 7.
                  \nBalance the following chemical equations:
                  \ni) Na + H2<\/sub>O \u2192 NaOH + H2<\/sub>
                  \nii) K2<\/sub>CO3<\/sub> + HCl \u2192 KCl + H2<\/sub>O + CO2<\/sub>
                  \nAnswer:
                  \ni) 2Na + 2H2<\/sub>O \u2192 2NaOH + H2<\/sub>
                  \nii) K2<\/sub>CO3<\/sub> + 2HCl \u2192 2KCl + H2<\/sub>O + CO2<\/sub><\/p>\n

                  Question 8.
                  \nObserve the following balanced chemical equation and answer the given questions.
                  \nC3<\/sub>H8(g)<\/sub> + 5O2(g)<\/sub> \u2192 3CO2(g)<\/sub> + 4H2<\/sub>O(g)<\/sub>
                  \ni) How many molecules of Oxygen are involved in this chemical reaction?
                  \nii) How many moles of Propane are required to get 20 moles of Water?
                  \nAnswer:
                  \ni) In this chemical reaction five molecules of oxygen are involved.
                  \nii) Five moles of propane are required to get 20 moles of water.<\/p>\n

                  Question 9.
                  \nWhat do you do to prevent rusting of copper and silver articles?
                  \nAnswer:
                  \nI can follow some rules given below to prevent rusting of copper and silver articles.<\/p>\n

                    \n
                  1. Shielding the metal surface from oxygen and moisture.<\/li>\n
                  2. By painting.<\/li>\n
                  3. By oiling, greasing.<\/li>\n
                  4. By galvanizing, chrome plating.<\/li>\n
                  5. By making alloys.<\/li>\n<\/ol>\n

                    Question 10.
                    \nWhat are the important characteristics of chemical reactions?
                    \nAnswer:
                    \nThe important characteristics of chemical reactions are<\/p>\n

                      \n
                    1. Evolution of a gas<\/li>\n
                    2. Formation of a precipitate<\/li>\n
                    3. Change in colour<\/li>\n
                    4. Change in temperature<\/li>\n
                    5. Change in state<\/li>\n<\/ol>\n

                      Question 11.
                      \nWhat symbols do we use to indicate the physical state of reactants and products in an equation?
                      \nAnswer:<\/p>\n

                        \n
                      1. Solid state is indicated by the symbol (s)<\/li>\n
                      2. Liquid state is indicated by the symbol (l)<\/li>\n
                      3. Gaseous state is indicated by the symbol (g)<\/li>\n
                      4. Aqueous solution is indicated by the symbol (aq)<\/li>\n<\/ol>\n

                        Question 12.
                        \nWhat can we do to make a chemical equation more informative?
                        \n(OR)
                        \nHow can chemical equation be made more informative by knowing?
                        \nAnswer:<\/p>\n

                          \n
                        1. Physical state,<\/li>\n
                        2. Heat changes (exothermic and endothermic reactions),<\/li>\n
                        3. Gas evolved,<\/li>\n
                        4. Precipitate formed.<\/li>\n<\/ol>\n

                          \"AP<\/p>\n

                          Question 13.
                          \nCommemt on “C(s)<\/sub> + O2(g)<\/sub> \u2192 CO2(g)<\/sub> + Heat” equation.
                          \nAnswer:<\/p>\n

                            \n
                          • The burning of carbon in oxygen is an exothermic reaction because heat is evolved in this reaction.<\/li>\n
                          • An exothermic reaction is indicated by writing + Heat or + Heat energy or just + Energy on the products side of an equation.<\/li>\n<\/ul>\n

                            Question 14.
                            \nComment on “N2(g)<\/sub> + O2(g)<\/sub> + Heat \u2192 2 NO(g)<\/sub>” equation.
                            \nAnswer:<\/p>\n

                              \n
                            • The reaction between nitrogen and oxygen to form nitric oxide is an endothermic reaction because heat is absorbed in this reaction.<\/li>\n
                            • An endotheumic reaction is usually indicated by writing + Heat or + Heat energy or just”+ Energy” on the reactants side of an equation.<\/li>\n<\/ul>\n

                              Question 15.
                              \nBalance the following equations.
                              \n1) Na + O2<\/sub> \u2192 Na2<\/sub>O
                              \n2) H2<\/sub>O2<\/sub> \u2192 H2<\/sub>O + O2<\/sub>
                              \n3) Mg(OH)2<\/sub> + HCl \u2192 MgCl2<\/sub> + H2<\/sub>O
                              \n4) Fe + O2<\/sub> \u2192 Fe2<\/sub>O2<\/sub>
                              \nAnswer:<\/p>\n

                                \n
                              1. 4 Na + O2<\/sub> \u2192 2 Na2<\/sub>O<\/li>\n
                              2. 2 H2<\/sub>O2<\/sub> \u2192 2 H2<\/sub>O + O2<\/sub><\/li>\n
                              3. Mg(OH)2<\/sub> + 2 HCl \u2192 MgCl2<\/sub> + 2 H2<\/sub>O<\/li>\n
                              4. 4 Fe + 3 O2<\/sub> \u2192 2 Fe2<\/sub>O3<\/sub><\/li>\n<\/ol>\n

                                Question 16.
                                \n2 Cu + O2<\/sub> \u2192 2 CuO
                                \nWhat information do you get from above equation?
                                \nAnswer:
                                \nThe above equation tells us that,<\/p>\n

                                  \n
                                1. Copper reacts with oxygen to form copper oxide.<\/li>\n
                                2. The formula of copper oxide is CuO and that of oxygen is O2<\/sub>.<\/li>\n
                                3. 2 moles of copper atoms react with 1 mole of oxygen molecules (O2<\/sub>) to produce 2 moles of copper oxide (CuO).<\/li>\n<\/ol>\n

                                  Question 17.
                                  \nWrite examples for oxidation reaction.
                                  \nAnswer:
                                  \nOxidation :
                                  \nIt is a reaction involving addition of oxygen or removal of hydrogen from a substance.
                                  \n1) Magnesium reacts with oxygen to form magnesium oxide.
                                  \n2 Mg + O2<\/sub> \u2192 2 MgO<\/p>\n

                                  2) Copper reacts with oxygen to form copper oxide.
                                  \n2 Cu + O2<\/sub> \u2192 2 CuO<\/p>\n

                                  3) Iron reacts with oxygen to form ferric oxide.
                                  \n4 Fe + 3 O2<\/sub> \u2192 2Fe2<\/sub>O3<\/sub><\/p>\n

                                  \"AP<\/p>\n

                                  Question 18.
                                  \nWrite examples for reduction reaction.
                                  \nAnswer:
                                  \nReduction :
                                  \nIt is a reaction involving addition of hydrogen or removal of oxygen from a substance.
                                  \n1) Nitrogen gas reacts with hydrogen gas to produce Ammonia.
                                  \nN2<\/sub> + 3H2<\/sub> \u2192 2NH3<\/sub><\/p>\n

                                  2) Oil reacts with hydrogen to form fat.
                                  \nOil + H2<\/sub> \u2192 Fat<\/p>\n

                                  Question 19.
                                  \nWrite the examples for corrosion reaction.
                                  \nAnswer:
                                  \n1) The black coatings on silver.
                                  \n4 Ag + 2H2<\/sub>S + O2<\/sub> \u2192 2 Ag2<\/sub>S + 2H2<\/sub>O<\/p>\n

                                  2) Green coating on copper.
                                  \n2 Cu + O2<\/sub> \u2192 2 CuO<\/p>\n

                                  Question 20.
                                  \nName the reactants and products in the following chemical equations.
                                  \nNa2<\/sub>SO4<\/sub> + BaCl2<\/sub> \u2192 BaSO4<\/sub> + NaCl
                                  \nAnswer:
                                  \nReactants are Sodium sulphate and Barium chloride. Products are Barium sulphate and Sodium chloride.<\/p>\n

                                  Question 21.
                                  \nBalance the following chemical equation and follow the steps involved in balancing a chemical equation.
                                  \nCu2<\/sub>S + O2<\/sub> \u2192 Cu2<\/sub>O + SO2<\/sub>
                                  \nAnswer:
                                  \nStep – 1 : Write the unbalanced equation using correct chemical formula for all substances.
                                  \nCu2<\/sub>S + O2<\/sub> \u2192 Cu2<\/sub>O + SO2<\/sub><\/p>\n

                                  Step – 2 : Compare number of atoms of each element on both sides.<\/p>\n\n\n\n\n\n\n
                                  Atom<\/td>\nNo. of atoms in LHS<\/td>\nNo. of atoms in RHS<\/td>\n<\/tr>\n
                                  Cu<\/td>\n2<\/td>\n2<\/td>\n<\/tr>\n
                                  S<\/td>\n1<\/td>\n1<\/td>\n<\/tr>\n
                                  O<\/td>\n2<\/td>\n3<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

                                  Balancing Cu, S, O atoms both sides
                                  \n2Cu2<\/sub>S + 3O2<\/sub> \u2192 2Cu2<\/sub>O + 2SO2<\/sub>
                                  \nThe equation is balanced.<\/p>\n

                                  Step – 3 : Write the coefficient of smallest ratio.
                                  \n2Cu2<\/sub>S + 3O2<\/sub> \u2192 2Cu2<\/sub>O + 2SO2<\/sub><\/p>\n

                                  Step – 4 : Verify above equation for balancing of atoms of each element on both sides.
                                  \n2Cu2<\/sub>S + 3O2<\/sub> \u2192 2Cu2<\/sub>O + 2SO2<\/sub><\/p>\n

                                  Question 22.
                                  \nWrite the difference between oxidation and reduction. Give example.
                                  \nAnswer:<\/p>\n\n\n\n\n\n
                                  Oxidation<\/td>\nReduction<\/td>\n<\/tr>\n
                                  1) Addition of oxygen or removal hydrogen from a compound is called oxidation.<\/td>\n1) Addition of hydrogen or removal of oxygen from a compound is called reduction.<\/td>\n<\/tr>\n
                                  2) e.g.: C + O2 <\/sub>\u2192 CO2<\/sub><\/td>\n2) e.g. :N2<\/sub> + 3H2 <\/sub>\u2192 2NH3<\/sub><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

                                  Question 23.
                                  \nGive two examples for chemical reactions in which precipitate is formed.
                                  \nAnswer:
                                  \nThe reactions in which a substance insoluble in water is formed are called precipitation reactions.
                                  \ne.g.:
                                  \n1) When lead nitrate solution reacts with potassium iodide solution it forms a yellow precipitate of lead iodide.
                                  \nPb(NO3<\/sub>)2(aq)<\/sub> + 2KI(aq)<\/sub> \u2192 PbI2(s)<\/sub> + 2KNO3(aq)<\/sub><\/p>\n

                                  2) When sodium sulphate solution reacts with barium chloride solution it forms a white precipitate of barium sulphate.
                                  \nNa2<\/sub>SO4(aq)<\/sub> + BaCl2(aq)<\/sub> \u2192 BaSO4(s)<\/sub> + 2NaCl(aq)<\/sub><\/p>\n

                                  Question 24.
                                  \nWhat are exothermic and endothermic reactions?
                                  \nAnswer:
                                  \nExothermic reaction :
                                  \nA chemical reaction in which heat is released is called exothermic reaction.
                                  \nEx :
                                  \nC + O2<\/sub> \u2192 CO2<\/sub> + Heat,
                                  \nCaO + H2<\/sub>O \u2192 Ca(OH)2<\/sub> + Heat<\/p>\n

                                  Endothermic reaction :
                                  \nA chemical reaction in which heat is absorbed is called endothermic reaction.
                                  \nEx :
                                  \n2NaHCO3<\/sub> + Heat \u2192 Na2<\/sub>CO3<\/sub> + H2<\/sub>O + CO2<\/sub><\/p>\n

                                  \"AP<\/p>\n

                                  Question 25.
                                  \nWhat is an alloy? Give one example.
                                  \nAnswer:
                                  \nA metallic substance made by mixing and fusing two or more metals or a metal and a non-metal, to obtain desirable qualities such as hardness, lightness and strength is called alloy.
                                  \nEx : Brass, bronze, steel.<\/p>\n

                                  Question 26.
                                  \nWhat is photochemical reaction? Give example.
                                  \nAnswer:
                                  \nThe decomposition reaction occurs in the presence of sunlight is called photochemical.. reaction.
                                  \nEx : 2AgBr(s)<\/sub> \u2192 2Ag(s)<\/sub> + Br2(g)<\/sub><\/p>\n

                                  Question 27.
                                  \nWhy is power supply to our home from the electrical pole interrupted?
                                  \nAnswer:<\/p>\n

                                    \n
                                  • Sometimes during rainy season the power supply to our home from the electric pole will be interrupted due to the formation of the metal oxide layer on the electric wire.<\/li>\n
                                  • This metal oxide is an electrical insulator.<\/li>\n<\/ul>\n

                                    Question 28.
                                    \nName the reactions involved in the following reactions with reasons.
                                    \n\"AP
                                    \nAnswer:
                                    \na) It is a decomposition reaction carried out in the presence of heat. So it is thermal decomposition reaction.
                                    \nb) It is a decomposition reaction carried out in the presence of light. So it is photochemical reaction.
                                    \nc) It is a decomposition taking place in the presence of electricity. So it is electrolysis reaction.
                                    \nd) Lead is more reactive than copper. So lead displaces copper from salt solution. So the reaction is chemical displacement reaction.<\/p>\n

                                    Question 29.
                                    \nRamu told Ravi that all material made of iron and its alloys are rusted when exposed to air. How do you correct him by asking suitable questions?
                                    \nAnswer:<\/p>\n

                                      \n
                                    1. What are the material we will generally use in our cooking utensils?<\/li>\n
                                    2. \u00a0What are the material used for surgical equipments?<\/li>\n
                                    3. What happens when stainless steel vessels are exposed to air?<\/li>\n<\/ol>\n

                                      Question 30.
                                      \nWhat are the gases released when lead nitrate is heated and how do you identify those gases?
                                      \nAnswer:
                                      \nWhen lead nitrate is heated it decomposes into lead oxide, nitrogen dioxide and oxygen.
                                      \n\"AP
                                      \nNitrogen diox-ide is identified by its reddish brown co|our. Oxygen makes the burning splinter to burn brightly when it is placed in test tube containing oxygen.<\/p>\n

                                      Question 31.
                                      \nWrite some chemical reactions occurring in our daily life.
                                      \nAnswer:<\/p>\n

                                        \n
                                      1. Souring of milk<\/li>\n
                                      2. Formation of curd from milk<\/li>\n
                                      3. Cooking of food<\/li>\n
                                      4. Digestion of food in our body<\/li>\n
                                      5. Fermentation of grapes<\/li>\n
                                      6. Rusting of iron<\/li>\n
                                      7. Burning of fuels<\/li>\n
                                      8. Burning of candle wax<\/li>\n
                                      9. Ripening of fruits.<\/li>\n<\/ol>\n

                                        Question 32.
                                        \nIf 40 gm of methane is burnt, then how much amount of CO2<\/sub> is released ?
                                        \nAnswer:
                                        \n\"AP
                                        \nWhen 16 g of methane is burnt it releases 44 g of CO2<\/sub>. The amount of CO2<\/sub> released when 40 g methane burnt 44
                                        \n= \\(\\frac{44}{16}\\) \u00d7 40=110g<\/p>\n

                                        Question 33.
                                        \nCalculate the amount of calcium oxide formed when 2 kg of calcium carbonate is decomposed. (The atomic masses of Ca = 40 U, C = 12 U, O = 16 U).
                                        \nAnswer:
                                        \nThe balanced equation is
                                        \nCaCO3(s)<\/sub> \u2192 CaO(s)<\/sub> + CO2(g)<\/sub>
                                        \n(40 + 12 + 3 x 16) U \u2192 (40 + 16) U + (12 + 2 x 16) U
                                        \n100 U \u2192 56 U + 44 U
                                        \n100 g \u2192 56g + 44g
                                        \n100 g calcium carbonate on decomposition produces 56 g of calcium oxide.
                                        \nAmount of calcium oxide formed due to decomposition of 2 kg of calcium carbonate
                                        \n\"AP<\/p>\n

                                        Question 34.
                                        \nA solution of common salt when added to silver nitrate solution yields a precipitate of silver chloride (0.28 g). Find the mass of sodium chloride in the solution and also the mass of sodium nitrate formed.
                                        \nAnswer:
                                        \n\"AP<\/p>\n

                                        Question 35.
                                        \n0.29 g of hydrocarbon when burnt completely in oxygen produces 448 ml of carbon dioxide at STP. From the information, calculate the
                                        \ni) mass of carbon dioxide formed
                                        \nii) mass of element carbon in carbon dioxide
                                        \niii) mass of hydrogen in hydrocarbon.
                                        \nAnswer:
                                        \ni) Gram molecular weight of carbon dioxide = 12 + 2 \u00d7 16g = 44 g.
                                        \n22.4 litres of CO2<\/sub> at STP weighs 44 g.<\/p>\n

                                        The weight of 448 ml of CO2<\/sub> at STP = \\(\\frac{44}{22400}\\) \u00d7 448 = 0.88 g<\/p>\n

                                        ii) 44g of CO2<\/sub> contains 12 g of carbon.
                                        \nThe amount of carbon present in 0.88 g of CO2<\/sub> = \\(\\frac{12}{44}\\) \u00d7 0.88 = 0.24 g<\/p>\n

                                        iii) Weight of hydrogen = Weight of hydrocarbon – Weight of carbon
                                        \n= 0.29 – 0.24 = 0.05 g<\/p>\n

                                        Question 36.
                                        \nCalculate the weights of carbon dioxide and water that will be obtained by completely burning 0.25 g of an organic compound having molecular formula C4<\/sub>H4<\/sub>O4<\/sub>.
                                        \nAnswer:
                                        \n\"AP<\/p>\n

                                        Question 37.
                                        \nWhat weight of sulphuric acid will be required to completely dissolve 3g of magnesium carbonate? Calculate the volume of carbon dioxide evolved at STP.
                                        \nAnswer:
                                        \n\"AP<\/p>\n

                                        Question 38.
                                        \nIf 16.4 g of calcium nitrate is heated : (a) Calculate the volume of Nitrogen dioxide obtained at STP and (b) The mass of calcium oxide obtained.
                                        \nAnswer:
                                        \n\"AP<\/p>\n

                                        Question 39.
                                        \nGive some examples for corroded and non-corroded metals and give the reasons for non-corrosion of metals.
                                        \nAnswer:
                                        \nExamples to corroded metals :<\/p>\n

                                          \n
                                        1. Iron<\/li>\n
                                        2. Copper<\/li>\n
                                        3. Silver<\/li>\n<\/ol>\n

                                          Reactions:
                                          \n4Fe + 3O2<\/sub> \u2192 2Fe2<\/sub>O3<\/sub>
                                          \n2Cu + O2<\/sub> \u2192 2CuO
                                          \n4Ag + 2H2<\/sub>S + O2<\/sub> \u2192 2Ag2<\/sub>S + 2H2<\/sub>O<\/p>\n

                                          Exmples to non-corroded metals :<\/p>\n

                                            \n
                                          1. Gold<\/li>\n
                                          2. Platinum<\/li>\n
                                          3. Brass<\/li>\n
                                          4. Bronze<\/li>\n
                                          5. Steel<\/li>\n<\/ol>\n

                                            Reasons:<\/p>\n

                                              \n
                                            1. Gold and platinum metals do not react with oxygen and have resistance to corrosion.<\/li>\n
                                            2. Brass, bronze and steel are alloys. So they have a quality of resistance to corrosion.<\/li>\n<\/ol>\n

                                              \"AP<\/p>\n

                                              Question 40.
                                              \nIron is a corroded metal. Through alloying we can prevent corrosion. Justify.
                                              \nAnswer:<\/p>\n

                                                \n
                                              • Alloying is a very good method of improving properties of metal.<\/li>\n
                                              • Generally pure form of iron is very soft and stretches easily when hot.<\/li>\n
                                              • When iron is mixed with carbon, nickel and chromium, an alloy stainless steel is obtained.<\/li>\n
                                              • The stainless steel is hard and does not rust.<\/li>\n
                                              • So, through alloying iron we can prevent corrosion.<\/li>\n<\/ul>\n

                                                Question 41.
                                                \n\u201cThrough alloying corrosion can be prevented.\u201d For the justification pose some questions.
                                                \nAnswer:<\/p>\n

                                                  \n
                                                1. What is alloying?<\/li>\n
                                                2. How are alloys prepared?<\/li>\n
                                                3. What are the qualities of alloys?<\/li>\n
                                                4. Which quantity prevents the corrosion in alloys?<\/li>\n
                                                5. Can we prevent corrosion by alloying a metal ?<\/li>\n<\/ol>\n

                                                  9th Class Physical Science6th Lesson Chemical Reactions and Equations 4 Marks Important Questions and Answers<\/h3>\n

                                                  Question 1.
                                                  \nWrite the balanced chemical reaction for the following and identify the type of reaction in each case.
                                                  \nA) Magnesium(s)<\/sub> + Iodine(g)<\/sub> \u2192 Magnesium iodide(s)<\/sub>
                                                  \nB) Zinc(s)<\/sub> + Hydrochloric acid(aq)<\/sub> \u2192 Zinc chloride(aq)<\/sub> + Hydrogen(g)<\/sub>
                                                  \nAnswer:
                                                  \nA) Magnesium(s)<\/sub> + Iodine(g)<\/sub> \u2192 Magnesium iodide(s)<\/sub>
                                                  \nMg + I2<\/sub> \u2192 Mgl2<\/sub>. This reaction is chemical combination.<\/p>\n

                                                  B) Zinc(s)<\/sub> + Hydrochloric acid(aq)<\/sub> \u2192 Zinc chloride(aq)<\/sub> + Hydrogen(g)<\/sub>
                                                  \nZn + 2HCl \u2192 ZnCl2<\/sub> + H2<\/sub> \u2191
                                                  \nThis reaction is chemical displacement.<\/p>\n

                                                  \"AP<\/p>\n

                                                  Question 2.
                                                  \nWrite an activity to each of the following chemical reaction.
                                                  \nA) Photo chemical reaction
                                                  \nB) Chemical displacement reaction.
                                                  \nAnswer:
                                                  \nA) Photo chemical reaction :
                                                  \n1) Take a pinch of Silver Bromide in a watch glass and it in the presence of sunlight.
                                                  \n2) Silver Bromide decomposes to silver and Bromine in sunlight.
                                                  \n\"AP<\/p>\n

                                                  B) Chemical displacement:<\/p>\n

                                                    \n
                                                  1. Take a small quantity of zinc dust in a conical flask and add some drops of dilute hydrochloric acid slowly.<\/li>\n
                                                  2. Immediately we can observe the gas bubbles coming out from the solution.<\/li>\n
                                                  3. This is because zinc reacts with dilute hydrochloric acid and liberates hydrogen gas.
                                                    \nZn + 2HCl \u2192 ZnCl2<\/sub> + H2<\/sub> \u2191<\/li>\n
                                                  4. In this reaction the element zinc has displaced hydrogen from hydrochloric acid.<\/li>\n<\/ol>\n

                                                    Question 3.
                                                    \nWhy should we balance a chemical equation ? Take any one chemical equation and explain the procedure of balancing it.
                                                    \nAnswer:
                                                    \nChemical reactions obey law of conservation of mass. So the total number of atoms of each elements in the reactants must be equal to the total number of atoms of each element in the<\/p>\n

                                                    products. So we should have to balance chemical equation.
                                                    \nEg : H2<\/sub> + O2<\/sub> \u2192 H2<\/sub>O<\/p>\n

                                                    Step -1 : Unbalanced equation = H2<\/sub> + O2<\/sub> \u2192 H2<\/sub>O
                                                    \nStep – 2 : Compare no.of atoms of each element on both sides.<\/p>\n\n\n\n\n\n
                                                    Atom<\/td>\nNo. of atoms in L.H.S<\/td>\nNo. of atoms in R.H.S<\/td>\n<\/tr>\n
                                                    H<\/td>\n2 (in H2<\/sub>)<\/td>\n2 (in H2<\/sub>O)<\/td>\n<\/tr>\n
                                                    0<\/td>\n2 (in O2<\/sub>)<\/td>\n1 (in H2<\/sub>O)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

                                                    No.of 0 atoms balancing – H2<\/sub> + O2<\/sub> \u2192 2H2<\/sub>O
                                                    \nNo.of H atoms balancing – 2H2<\/sub> + O2<\/sub> \u2192 2H2<\/sub>O<\/p>\n

                                                    Step – 3 : The above equation is balanced and write the coefficients in the smallest ratio. 2H2<\/sub> + O2<\/sub> \u2192 2H2<\/sub>O<\/p>\n

                                                    Step – 4 : Verify above equation for balancing of atoms each element on both sides. Hence the equation is balanced.
                                                    \n\u2234 2H2<\/sub> + O2<\/sub> \u2192 2H2<\/sub>O<\/p>\n

                                                    Question 4.
                                                    \nBalance the following chemical equations.
                                                    \ni) Zn(s)<\/sub> + Ag NO3(aq)<\/sub> \u2192 Zn (NO3<\/sub>)2(aq)<\/sub> + Ag(s)<\/sub>
                                                    \nii) Fe2<\/sub>O3(s)<\/sub> + C(s)<\/sub> \u2192 Fe(s)<\/sub> + CO2(g)<\/sub>
                                                    \niii) Ag(s)<\/sub> + H2<\/sub>S(g)<\/sub> \u2192 Ag2<\/sub>S(s)<\/sub> + H2<\/sub>O(l)<\/sub>
                                                    \niv) Cu(s)<\/sub> + O2(g)<\/sub> \u2192 CuO(g)<\/sub>
                                                    \nAnswer:
                                                    \ni) Zn(s)<\/sub> + Ag NO3(aq)<\/sub> \u2192 Zn (NO3<\/sub>)2(aq)<\/sub> + Ag(s)<\/sub>
                                                    \nBalanced equation : Zn(s)<\/sub> + 2 AgNO3(aq)<\/sub> \u2192 Zn (NO3<\/sub>)2(aq)<\/sub> + 2Ag(s)<\/sub><\/p>\n

                                                    ii) Fe2<\/sub>O3(s)<\/sub> + C(s)<\/sub> \u2192 Fe(s)<\/sub> + CO2(g)<\/sub>
                                                    \nBalanced equation : 2Fe2<\/sub>O3(s)<\/sub> + 3C(s)<\/sub> \u2192 4Fe(s)<\/sub> + 3CO2(g)<\/sub><\/p>\n

                                                    iii) Ag(s)<\/sub> + H2<\/sub>S(g)<\/sub> \u2192 Ag2<\/sub>S(s)<\/sub> + H2<\/sub>O(l)<\/sub>
                                                    \nBalanced equation :
                                                    \nWe cannot balance the equation because atom \u2018O\u2019 does not exist in the reactants.<\/p>\n

                                                    iv) Cu(s)<\/sub> + O2(g)<\/sub> \u2192 CuO(s)<\/sub>
                                                    \nBalanced equation :
                                                    \n2Cu(s)<\/sub> + O2(g)<\/sub> \u2192 2CuO(s)<\/sub><\/p>\n

                                                    Question 5.
                                                    \nWrite the equation for the reaction of zinc with hydrochloric acid and balance the equation. Find out the number of molecules of hydrogen gas produced in this reaction, when 1 mole of HCl completely reacts at S.T.P.
                                                    \n[Gram molar volume is 22.4 liters at S.T.P., Avogadro’s number is 6.023 \u00d7 1023<\/sup>]
                                                    \nAnswer:
                                                    \nZn + 2HCl \u2192 ZnCl2<\/sub> + H2<\/sub><\/p>\n

                                                      \n
                                                    • In the reaction 2 moles of HC\/ produce 1 mole of H2<\/sub>.<\/li>\n
                                                    • If 1 mole of HCl participate in reaction, Vi mole of hydrogen will be produced.<\/li>\n
                                                    • 1 mole of H2<\/sub> gas contains 6.023 \u00d7 1023<\/sup> molecules at STP.
                                                      \nNumber of molecules in \u00bd mole of H2<\/sub> gas = 6.023 \u00d7 1023<\/sup> \u00d7 \u00bd = 3.011 \u00d7 1023<\/sup><\/li>\n<\/ul>\n

                                                      Question 6.
                                                      \nWrite the examples for chemical combination.
                                                      \nAnswer:
                                                      \n1) Magnesium burns in oxygen to form magnesium oxide.
                                                      \n2 Mg + O2<\/sub> \u2192 2 MgO<\/p>\n

                                                      2) When coal is burnt in oxygen, carbon dioxide is produced.
                                                      \nC + O2<\/sub> \u2192 CO2<\/sub> + Q (cheat energy)<\/p>\n

                                                      3) Slaked lime is prepared by adding water to quick lime.
                                                      \nCaO + H2<\/sub>O \u2192 Ca(OH)2<\/sub> + Q (heat energy)<\/p>\n

                                                      4) When hydrogen reacts with oxygen, it gives water.
                                                      \nH2<\/sub> + O2<\/sub> \u2192 2 H2<\/sub>O<\/p>\n

                                                      5) Hydrochloric acid is obtained by adding hydrogen to chlorine.
                                                      \nH2<\/sub> + Cl2<\/sub> \u2192 2 HCl<\/p>\n

                                                      6) Magnesium reacts with iodine to magnesium iodide.
                                                      \nMg + l2<\/sub> \u2192 Mgl2<\/sub><\/p>\n

                                                      7) Sodium reacts with chlorine to form sodium chloride.
                                                      \n2 Na +Cl2<\/sub> \u2192 2 NaCl<\/p>\n

                                                      8) Iron reacts with oxygen to form haematite.
                                                      \nFe + 3O2<\/sub> \u2192 2 Fe2<\/sub>O3<\/sub><\/p>\n

                                                      Question 7.
                                                      \nWrite examples for chemical decomposition reaction.
                                                      \nAnswer:
                                                      \n1) Calcium carbonate on heating decomposes to calcium oxide and carbon dioxide.
                                                      \n\"AP
                                                      \n2) On electrolysis, water decomposes to water and hydrogen.
                                                      \n2 H2<\/sub>O \u2192 2 H2<\/sub> + O2<\/sub><\/p>\n

                                                      3) Silver bromide decomposes to silver and bromine in sunlight.
                                                      \n2 AgBr \u2192 2 Ag + Br2<\/sub><\/p>\n

                                                      4) Silver chloride decomposes to silver and chlorine.
                                                      \n2 AgCl \u2192 2 Ag + Cl2<\/sub><\/p>\n

                                                      5) Glucose decomposes to ethanol and carbon dioxide.
                                                      \nC6<\/sub>H12<\/sub>O6<\/sub> \u2192 2 C2<\/sub>H5<\/sub>OH + 2 CO2<\/sub><\/p>\n

                                                      6) Sodium bicarbonate decomposes to sodium carbonate, water and carbon dioxide.
                                                      \n2 NaHCO3<\/sub> + Heat \u2192 Na2<\/sub>CO3<\/sub> + H2<\/sub>O + CO2<\/sub><\/p>\n

                                                      7) On heating lead nitrate decomposes to lead oxide, oxygen and nitrogen dioxide.
                                                      \n\"AP<\/p>\n

                                                      Question 8.
                                                      \nWrite the examples for chemical displacement reaction.
                                                      \nAnswer:
                                                      \n1) Zinc pieces react with dilute hydrochloric acid and liberate hydrogen gas
                                                      \nZn + 2 HCl \u2192 ZnCl2<\/sub> + H2<\/sub><\/p>\n

                                                      2) Iron reacts copper sulphate to form iron sulphate and copper.
                                                      \nFe + CuSO4<\/sub> \u2192 FeSO4<\/sub> + Cu<\/p>\n

                                                      3) Zinc is mixed with silver nitrate to form zinc nitrate and silver.
                                                      \nZn + 2 AgNO3<\/sub> \u2192 Zn(NO3<\/sub>)2<\/sub> + 2Ag<\/p>\n

                                                      4) Lead reacts with copper chloride to form lead chloride and copper.
                                                      \nPb + CuCl2<\/sub> \u2192 PbCl2<\/sub> + Cu<\/p>\n

                                                      5) Sodium reacts with water to form sodium hydroxide and hydrogen.
                                                      \n2 Na + 2H2<\/sub>O \u2192 2 NaOH + H2<\/sub><\/p>\n

                                                      6) Aluminium reacts with copper chloride to form aluminium chloride and copper.
                                                      \n2 Al + 3 CuCl2<\/sub> \u2192 2 AlCl3<\/sub> + 3 Cu<\/p>\n

                                                      7) Zinc reacts with sulphuric acid to form zinc sulphate and hydrogen.
                                                      \nZn + H2<\/sub>SO4<\/sub> \u2192 ZnSO4<\/sub> + H2<\/sub><\/p>\n

                                                      \"AP<\/p>\n

                                                      Question 9.
                                                      \nWrite examples for chemical double displacement reaction.
                                                      \nAnswer:
                                                      \n1) Sodium sulphate solution on mixing with barium chloride solution forms a white precipitate of barium sulphate and soluble sodium chloride.
                                                      \nNa2<\/sub>SO4<\/sub> + BaCl2<\/sub> \u2192 BaSO4<\/sub> + 2 NaCl<\/p>\n

                                                      2) Sodium hydroxide reacts with hydrochloric acid to form sodium chloride and water.
                                                      \nNaOH + HCl \u2192 NaCl + H2<\/sub>O<\/p>\n

                                                      3) Sodium chloride spontaneously combines with silver nitrate in solution giving silver chloride precipitate.
                                                      \nNaCl + AgNO3<\/sub> \u2192 AgCl + NaNO3<\/sub><\/p>\n

                                                      4) Mix lead nitrate solution and potassium iodide solution to form a yellow precipitate of lead iodide and potassium nitrate.
                                                      \nPb(NO3<\/sub>)2<\/sub> + 2Kl \u2192 PbI2<\/sub> + 2KNO3<\/sub><\/p>\n

                                                      5) Calcium hydroxide reacts with nitric acid to form water and calcium nitrate.
                                                      \nCa(OH)2<\/sub> + 2 HNO3<\/sub> \u2192 2H2<\/sub>O + Ca(NO3<\/sub>)2<\/sub><\/p>\n

                                                      6) Magnesium chloride reacts with potassium hydroxide to form magnesium hydroxide and potassium chloride.
                                                      \nMgCl2<\/sub> + 2 KOH \u2192 Mg(OH)2<\/sub> + 2 KCl<\/p>\n

                                                      Question 10.
                                                      \nBalance the following equations.
                                                      \n1) Al(OH)3<\/sub> \u2192 Al2<\/sub>O3<\/sub> + H2<\/sub>O
                                                      \n2) NH3<\/sub> + CuO \u2192 Cu + N2<\/sub> + H2<\/sub>O
                                                      \n3) Al2<\/sub>(SO4<\/sub>)3<\/sub> + NaOH \u2192 Al(OH)3<\/sub> + Na2<\/sub>SO4<\/sub>
                                                      \n4) HNO3<\/sub> + Ca(OH)2<\/sub> \u2192 Ca(NO3<\/sub>)2<\/sub> + H2<\/sub>O
                                                      \n5) NaOH + H2<\/sub>SO4<\/sub> \u2192 Na2<\/sub>SO4<\/sub> + H2<\/sub>O
                                                      \n6) BaCl2<\/sub> + H2<\/sub>SO4<\/sub> \u2192 BaSO4<\/sub> + HCl
                                                      \nAnswer:<\/p>\n

                                                        \n
                                                      1. 2 Al(OH)3<\/sub> \u2192 Al2<\/sub>O3<\/sub> + 3 H2<\/sub>O<\/li>\n
                                                      2. 2 NH3<\/sub> + 3 CuO \u2192 3 Cu + N2<\/sub> + 3 H2<\/sub>O<\/li>\n
                                                      3. Al2<\/sub>(SO)3<\/sub> + 6 NaOH \u2192 2 Al(OH)3<\/sub> + 3 Na2<\/sub>SO4<\/sub><\/li>\n
                                                      4. 2 HNO3<\/sub> + Ca(OH)2<\/sub> \u2192 Ca(NO3<\/sub>)2<\/sub> + 2 H2<\/sub>O<\/li>\n
                                                      5. 2 NaOH + H2<\/sub>SO4<\/sub> \u2192 Na2<\/sub>SO4<\/sub> + 2 H2<\/sub>O<\/li>\n
                                                      6. BaCl2<\/sub> + H2<\/sub>SO4<\/sub> \u2192 BaSO4<\/sub> + 2 HCl<\/li>\n<\/ol>\n

                                                        \"AP<\/p>\n

                                                        Question 11.
                                                        \nHow many types of chemical reactions are there? Explain with examples.
                                                        \nAnswer:
                                                        \nThere are four types of chemical reactions. They are :
                                                        \ni) Chemical combination :
                                                        \nA chemical reaction in which two or more substances combine together to form a new substance is called chemical combination.
                                                        \ne.g.: 2H2<\/sub> + O2<\/sub> \u2192 2H2<\/sub>O
                                                        \nCaO + H2<\/sub>O \u2192 Ca(OH)2<\/sub><\/p>\n

                                                        ii) Chemical decomposition :
                                                        \nThe reaction in which a compound breaks up into two or more simpler substances are known as decomposition reaction. These reactions are generally carried out by means of heat, light, electricity or catalysts.
                                                        \ne.g.: CaCO3<\/sub> \u2192 CaO + CO2<\/sub>
                                                        \n2Pb(NO3<\/sub>)2<\/sub> \u2192 2 PbO + 4NO2<\/sub> + O2<\/sub><\/p>\n

                                                        iii) Chemical displacement:
                                                        \nThe chemical reaction in which one element takes the place of another element in a compound is called displacement reaction.
                                                        \nIn these reactions, an atom or group of atoms in a molecule is replaced by another atom or a group of atoms.
                                                        \ne.g.: Zn + 2HCl \u2192 ZnCl2<\/sub> + H2<\/sub> \u2191
                                                        \nZn + CuSO4<\/sub> \u2192 ZnSO4<\/sub> + Cu<\/p>\n

                                                        iv) Chemical double displacement: The reaction in which two compounds react to form two other compounds by mutual exchange of their ions is called double displacement reaction.
                                                        \ne.g.: NaOH(aq)<\/sub> + HCl(aq)<\/sub> \u2192 NaCl(aq)<\/sub> + H2<\/sub>O(l)<\/sub>
                                                        \nNaNO3(aq)<\/sub> + AgCl(aq)<\/sub> \u2192 AgNO3(s)<\/sub> + NaCl(aq)<\/sub><\/p>\n

                                                        Question 12.
                                                        \nBalance the following chemical equations.
                                                        \na) Na2<\/sub>SO4<\/sub> + BaCl2<\/sub> \u2192 BaSO4<\/sub> + NaCl
                                                        \nb) Al4<\/sub>C3<\/sub> + H2<\/sub>O \u2192 CH4<\/sub> + Al(OH)3<\/sub>
                                                        \nc) Pb(NO3<\/sub>)2<\/sub> \u2192 PbO + NO2<\/sub> + O2<\/sub>
                                                        \nd) Fe2<\/sub>O3<\/sub> + Al \u2192 Al2<\/sub>O3<\/sub> + Fe
                                                        \nAnswer:
                                                        \na) Na2<\/sub>SO4<\/sub> + BaCl2<\/sub> \u2192 BaSO4<\/sub> + 2NaCl
                                                        \nb) Al4<\/sub>C3<\/sub> + 12H2<\/sub>O \u2192 3CH4<\/sub> + 4Al(OH)3<\/sub>
                                                        \nc) 2Pb(NO3<\/sub>)2<\/sub> \u2192 2PbO + 4NO2<\/sub> + O2<\/sub>
                                                        \nd) Fe2<\/sub>O3<\/sub> + 2Al \u2192 Al2<\/sub>O3<\/sub> + 2Fe<\/p>\n

                                                        \"AP<\/p>\n

                                                        Question 13.
                                                        \nHow can we make a chemical equation information?
                                                        \nChemical equations can be made more informative by expressing following characteristics of the reactants and products.
                                                        \n1. Expressing the physical state :
                                                        \nThe different states, i.e. gaseous, liquid and solid states are represented by the notations (g), (l) and (s) respectively. If the substance is present as a solution in water the word aqueous is written.
                                                        \n\"AP<\/p>\n

                                                        2. Expressing the heat changes :
                                                        \nQ is heat energy which is shown with plus \u2019+\u2019 sign on product side for exothermic reactions and minus sign on product side for endothermic reactions.
                                                        \ne.g.: a) C(s)<\/sub> + O2(g)<\/sub> \u2192 CO2(g)<\/sub> + Q (exothermic reaction)
                                                        \nN2(g)<\/sub> + O2(g)<\/sub> \u2192 2NO(g)<\/sub> \u201d Q (endothermic reaction)<\/p>\n

                                                        3. Expressing the gas evolved :
                                                        \nIf a gas evolved in a reaction, it is denoted by an upward arrow \u2191 or (g).
                                                        \nZn(s)<\/sub> + H2<\/sub>SO4(aq)<\/sub> \u2192 ZnSO4(aq)<\/sub> + H2(g)<\/sub>\u2191<\/p>\n

                                                        4. Expressing precipitate formed: If a precipitate is formed in the reaction, it is denoted by downward arrow \u2193.
                                                        \nAgNO3(aq)<\/sub> + NaCl(aq)<\/sub> \u2192 AgCl(s)<\/sub> \u2193 + NaNO3(aq)<\/sub><\/p>\n

                                                        Question 14.
                                                        \nGive daily life examples of oxidation.
                                                        \nAnswer:
                                                        \nDaily life examples :<\/p>\n

                                                          \n
                                                        1. Combustion of fuels.<\/li>\n
                                                        2. Corrosion of metals.<\/li>\n
                                                        3. Change of colour of fruits like apples, bananas, when they are cut.<\/li>\n
                                                        4. Burning of crackers.<\/li>\n
                                                        5. Rancidity of food material.<\/li>\n
                                                        6. During rainy season the power supply to our home from the electric pole will be interrupted due to formation of metal oxide layer on the electric wire.<\/li>\n
                                                        7. Rising of dough with yeast depends on oxidation of sugars to carbon dioxide and water.<\/li>\n
                                                        8. Bleaching of coloured objects using moist chlorine.<\/li>\n
                                                        9. Respiration.<\/li>\n<\/ol>\n

                                                          Question 15.
                                                          \nWhat is the information giyen by balanced chemical equation?
                                                          \nAnswer:<\/p>\n

                                                            \n
                                                          • A chemical equation gives information about the reactants and products through their symbols and formulae.<\/li>\n
                                                          • It gives the ratio of molecules of reactants and products.<\/li>\n
                                                          • As molecular masses are expressed in unified masses, the relative masses of reactants and products are known from the equation.<\/li>\n
                                                          • If the masses are expressed in grams, then the equation also gives the molar ratios of reactants and products.<\/li>\n
                                                          • If gases are involved, we can equate the masses to their volumes.<\/li>\n
                                                          • Using molar mass and Avagadro’s number we can calculate the number of molecules and atoms of different substances from the equation.<\/li>\n<\/ul>\n

                                                            Question 16.
                                                            \nWrite the balanced equation and identify the type of reaction.
                                                            \n1) Magnesium Hydroxide(aq)<\/sub> + Nitric Acid(aq)<\/sub> \u2192 Magnesium Nitrate(aq)<\/sub> + Water(l)<\/sub>
                                                            \n2) Magnesium(s)<\/sub> + Carbon Monoxide(g)<\/sub> \u2192 Magnesium Oxide(s)<\/sub> + Carbon(g)<\/sub>
                                                            \n3) Barium Chloride(aq)<\/sub> + Sodium Sulphate(aq)<\/sub> \u2192 Barium Sulphate(s)<\/sub> + Sodium Chloride(aq)<\/sub>
                                                            \n4) Sodium Nitrate(s)<\/sub> \u2192 Sodium Nitrite(s)<\/sub> + Oxygen(g)<\/sub>
                                                            \nAnswer:
                                                            \n1) Mg(OH)2(aq)<\/sub> + 2 HNO3(aq)<\/sub> \u2192 Mg(NO3<\/sub>)2(aq)<\/sub> + 2 H2<\/sub>O(l)<\/sub>
                                                            \nIt is both double displacement and neutralisation reaction.<\/p>\n

                                                            2) Mg(s)<\/sub> + CO(g)<\/sub> \u2192 MgO(s)<\/sub> + C(s)<\/sub>
                                                            \nIt is a redox reaction in which magnesium is oxidised and carbon monoxide is reduced.<\/p>\n

                                                            3) BaCl2(aq)<\/sub> + Na2<\/sub>SO4(aq)<\/sub> \u2192 BaSO4(s)<\/sub> \u2193 + 2 NaCl(aq)<\/sub>
                                                            \nIt is both precipitation and double displacement reaction.<\/p>\n

                                                            4) 2 NaNO3(s) <\/sub> \u2192 2 NaNO2(s)<\/sub> + O2(g)<\/sub>
                                                            \nIt is both endothermic and decomposition reaction.<\/p>\n

                                                            \"AP<\/p>\n

                                                            Question 17.
                                                            \nWe write symbol of water as H2<\/sub>O. State why we should not write it as HO2<\/sub>.
                                                            \nAnswer:
                                                            \n1) The hydrogen atom has only T electron in its outermost shell, so it needs 1 more electron to achieve the stability. ‘2’ electrons are required to get inert gas electronic configuration.<\/p>\n

                                                            2) The oxygen atom has ‘6’ electrons in its outermost shell and it needs ‘2’ more electrons to compare the stability. ‘8’ electron arrangement of inert gas is neon.
                                                            \n\"AP
                                                            \nIn the water molecule, central oxygen atom has two pairs of unshared electrons which have not been utilised in the formation of bonds.<\/p>\n

                                                            So, we write symbol of water as H20 and we should not write it as HO2<\/sub>.<\/p>\n

                                                            Question 18.
                                                            \nLatha took some quantity of powder of a substance in a test tube. Heated it with spirit lamp. A gas was liberated. She sent the gas into another test tube. The colour of solution in the second test tube turned into milk white.
                                                            \nAnswer the following questions :
                                                            \na) Which substance was heated?
                                                            \nb) Which gas was liberated?
                                                            \nc) What was the solution taken in second test tube?
                                                            \nd) Which type of chemical reactions involved the experiment?
                                                            \nAnswer:
                                                            \na) The substance is calcium carbonate.
                                                            \nb) The gas liberated is carbon dioxide.
                                                            \nc) The solution taken in the second test tube was solution of slaked lime.
                                                            \nd) Two types of reactions took place in this experiment, i.e. decomposition and double displacement.
                                                            \nCaCO3(s)<\/sub> \u2192 CaO(s)<\/sub> . CO2<\/sub> \u2191
                                                            \nCa(OH)2(aq)<\/sub> + CO2(g)<\/sub> \u2192 CaCO3(s)<\/sub> + H2<\/sub>O<\/p>\n

                                                            Question 19.
                                                            \nA light yellow colour substance (some quantity) on a watch glass is put in the sunlight. It changes into grey colour substance.
                                                            \na) What is the light yellow colour substance?
                                                            \nb) What is the grey colour substance?
                                                            \nc) Which type of chemical reaction it is?
                                                            \nd) Write the chemical equation for the reaction.
                                                            \nAnswer:
                                                            \na) The light yellow colour substance is silver bromide.
                                                            \nb) The grey colour substance is silver.
                                                            \nc) The type of chemical reaction is photochemical reaction.
                                                            \n\"AP<\/p>\n

                                                            Question 20.
                                                            \nHeat is liberated in the reactions where water is added to calcium oxide and hydrochloric acid added to zinc pieces.
                                                            \nRarnu says that they are same type of chemical reactions. Eswar’s opinion is that the reactions are not similar. What is the basis of Eswar’s opinion ? Write equations for the above reaction.
                                                            \nAnswer:
                                                            \nEswar\u2019s thinking is correct. Although both are exothermic reactions, the type of chemical reactions is different.
                                                            \nCase (i) : When water is added to calcium oxide it forms calcium hydroxide. It is an example for combination reaction.
                                                            \nCaO(s)<\/sub> + H2<\/sub>O \u2192 Ca(OH)2(aq)<\/sub><\/p>\n

                                                            Case (ii) : When hydrochloric acid is added to zinc pieces it would liberate hydrogen gas which is an example for displacement reaction.
                                                            \nZn(s)<\/sub> + HCl(aq)<\/sub> \u2192 ZnCl2(aq)<\/sub> + H2(g)<\/sub> \u2191<\/p>\n

                                                            \"AP<\/p>\n

                                                            Question 21.
                                                            \nWe see many combustion and oxidation reactions in our daily life. Among them every combustion reaction is an oxidation reaction. But not all the oxidation reactions are combustion reactions. Do you agree or disagree with the statement? Explain with proper reasons.
                                                            \nAnswer:
                                                            \n1) Yes, I agree with the statement because combustion reaction is nothing but burning of a substance in the presence of oxygen so it is an oxidation reaction. So every combustion reaction is an oxidation reaction.<\/p>\n

                                                            2) Whereas some reactions which do not require burning still they are oxidation reactions.
                                                            \nEg :<\/p>\n

                                                              \n
                                                            1. Corrosion of metals.<\/li>\n
                                                            2. Change of colour of fruits like apples, bananas when they are cut.<\/li>\n
                                                            3. Rancidity of food materials.<\/li>\n
                                                            4. Respiration.<\/li>\n
                                                            5. Bleaching of coloured objects using moist chlorine.
                                                              \nSo all oxidation reactions are not combustion reactions.<\/li>\n<\/ol>\n

                                                              Question 22.
                                                              \nExplain the following :
                                                              \n1) What happens when iron filings are added to zinc sulphate solution?
                                                              \n2) What happens when solid silver nitrate is added to solid sodium chloride?
                                                              \nAnswer:
                                                              \n1) No reaction takes place because zinc is more reactive than iron. So iron cannot displace zinc from its salt solution.<\/p>\n

                                                              2) No reaction takes place because in solid state silver nitrate as well as sodium chloride is unable to dissociate into constituent ions. So exchange of ions is not possible.<\/p>\n

                                                              Question 23.
                                                              \nWhy is steel not used for surgical equipment and what is the material used for surgical equipment? Why is that material used for surgical equipment?
                                                              \nAnswer:
                                                              \n1) Steel undergoes rusting when It exposed to air. So it is not useful for preparation of surgical equipment. If we use it in surgical equipment it may cause septic of wound.<\/p>\n

                                                              2) The material used for surgical equipment is stainless steel which is an alloy of iron, carbon, nickel and chromium. Chromium does not easily react with oxygen. So, addition of chromium makes the stainless steel free from rusting. Therefore it is used in surgical equipment.<\/p>\n

                                                              \"AP<\/p>\n

                                                              Question 24.
                                                              \nGive reasons for the following.
                                                              \n1) Why do we add salt to water during electrolysis of water?
                                                              \n2) Why does hydrogen gas put off the burning splinter and it burns with blue flame?
                                                              \n3) Why does carbon dioxide turn lime water milky?
                                                              \nAnswer:
                                                              \n1) Pure water is a bad conductor of electricity. By adding a small amount of salt the solution becomes conductor of electricity.<\/p>\n

                                                              2) Hydrogen does not support combustion. So it puts off the burning splinter and also it is combustible. So burns with blue flame.<\/p>\n

                                                              3) When we pass carbon dioxide through lime water it turns into milky because lime water (calcium hydroxide) reacts with carbon dioxide and forms a white milky substance, i.e. calcium carbonate.<\/p>\n

                                                              Question 25.
                                                              \nA student was given the following substances and was asked to show types of chemical reactions through experiment. Write how he would have done that. Copper sulphate solution, barium chloride solution, ferrous sulphate crystals, iron nails, calcium oxide, water.
                                                              \nAnswer:
                                                              \nGiven chemicals are CuSO4<\/sub> solution, BaSO4<\/sub> solution, iron nails (Fe), Ferrous sulphate (FeSO4<\/sub>), Calcium oxide (CaO) and water (H2<\/sub>O).<\/p>\n

                                                              i) Chemical combination :
                                                              \nChemicals chosen : CaO, H2<\/sub>O
                                                              \nCaO + H2<\/sub>O \u2192 Ca(OH)2<\/sub><\/p>\n

                                                              When we add water to calcium oxide it produces Calcium hydroxide. This is an example for chemical combination.<\/p>\n

                                                              ii) Chemical decomposition:
                                                              \nChemicals chosen : Ferrous sulphate
                                                              \n\"AP
                                                              \nWhen we heat FeSO4<\/sub> it dissociates into Ferric oxide, Sulphur dioxide and Sulphur trioxide respectively.<\/p>\n

                                                              iii) Chemical displacement :
                                                              \nChemicals chosen : Iron nail – CuSO4<\/sub>
                                                              \nFe + CuSO4<\/sub> \u2192 FeSO4<\/sub> + Cu \u2193<\/p>\n

                                                              When iron nail is placed in CuSO4<\/sub> solution, the solution turns into light green due to formation of FeSO4<\/sub> and reddish brown deposit of Copper.<\/p>\n

                                                              iv) Double displacement:
                                                              \nChemicals chosen : CuSO4<\/sub> solution and BaCl2 solution.
                                                              \nCuSO4(aq)<\/sub> + BaCl2(aq)<\/sub> \u2192 BaSO4(s)<\/sub> \u2193 + CuCl2(s)<\/sub><\/p>\n

                                                              When CuSO4<\/sub> is mixed with BaCl2<\/sub> solution it forms white precipitate of BaSO4<\/sub> and aqueous solution of Copper (II) Chloride.<\/p>\n

                                                              This is an example for double displacement reaction.<\/p>\n

                                                              \"AP<\/p>\n

                                                              Question 26.
                                                              \nTake two beakers and prepare lead nitrate aqueous solution and potassium iodide aqueous solutions. What are the colours of the solutions? Now mix them in another beaker. What happens? What type of chemical reaction it is? What are products?
                                                              \nAnswer:
                                                              \nThe colours of the solutions are white or colourless. When lead nitrate solution is mixed with potassium iodide solution we will get yellow precipitate of lead iodide. This is double displacement reaction. The products are lead iodide and potassium nitrate.
                                                              \nPb(NO3<\/sub>)2(aq)<\/sub> + 2Kl(aq)<\/sub> \u2192 Pbl2(s)<\/sub> + 2KNO3(aq)<\/sub><\/p>\n

                                                              Question 27.
                                                              \nObserve the following equation which shows the action of heat on Calcium Nitrate
                                                              \n2 Ca(NO3<\/sub>)2<\/sub> \u2192 2 CaO + 4 NO2<\/sub> + O2<\/sub>
                                                              \na) How many moles of NO2<\/sub> are formed when a mole of 2 Ca(NO3<\/sub>)2<\/sub> is decomposed?
                                                              \nb) What is the volume of NO2<\/sub> produced when 164 gm of Ca(NO3<\/sub>)2<\/sub> is heated at constant temperature and pressure?
                                                              \nc) Calculate the mass of Calcium Oxide formed when 82 gm of Ca(NO3<\/sub>)2<\/sub> is heated.
                                                              \nd) What is the quantity of Ca(NO3<\/sub>)2<\/sub> required to produce 5 moles of gaseous products?
                                                              \nAnswer:
                                                              \nGiven balanced equation is
                                                              \na) From the balanced equation 2 moles of Ca(NO3<\/sub>)2<\/sub> releases 4 moles of NO2<\/sub>.
                                                              \nb) Molecular weight of Ca(NO3<\/sub>)2<\/sub> and CaO respectively are 164 and 56.
                                                              \nFrom the equation at STP 2 \u00d7 164 g. of Ca(NO3<\/sub>)2<\/sub> releases 4 \u00d7 22.4 litres of NO2<\/sub>.
                                                              \nAt similar conditions 164 g. of Ca(NO3<\/sub>)2<\/sub> releasing NO2<\/sub> in litres is
                                                              \n= \\(\\frac{164}{2 \\times 164}\\) \u00d7 22.4 \u00d7 4 = 2 \u00d7 22.4 = 44.8 liters.<\/p>\n

                                                              c) From the balanced equation 164 g. of Ca(NO3<\/sub>)2 <\/sub>decomposes and forms 112 g. of CaO. Similarly 82 g. of Ca(NO3<\/sub>)2<\/sub> decomposes and forms
                                                              \n\\(\\frac{82}{164}\\) \u00d7 112 = 56 g. of CaO.<\/p>\n

                                                              d) From the above balanced equation 2 moles of Ca(NO3<\/sub>)2<\/sub> releases 5 moles of gaseous products.
                                                              \n\u2234 The mass of Ca(NO3<\/sub>)2<\/sub> required is 2 \u00d7 164 = 328 g.<\/p>\n

                                                              \"AP<\/p>\n

                                                              Question 28.
                                                              \nZn + HCl \u2192 ZnCl2<\/sub> + H2<\/sub>
                                                              \nCalculate amount of zinc required to release 500g of hydrogen. (Zn = 65 U, H = 1 U, Cl = 35.5 U are the atomic masses).
                                                              \nAnswer:
                                                              \nThe balanced chemical equation is
                                                              \nZn + 2 HCl \u2192 ZnCl2<\/sub> + H2<\/sub>
                                                              \n65 U + (2 \u00d7 36.5) U \u2192 (65 + 2 \u00d7 35.5) U + 2 U
                                                              \n65 g + 73 g \u2192 136 g + 2g
                                                              \nAs per the balanced equation
                                                              \n65 g Zinc is reacting with hydrochloric acid to produce 2g of Hydrogen.
                                                              \n\"AP<\/p>\n

                                                              Question 29.
                                                              \nCalculate the volume, mass and number of molecules of carbon dioxide when 104 g of acetylene (C2<\/sub>H2<\/sub>) burnt in air. (Atomic masses of C = 12 U, H = 1 U, O = 16 U).
                                                              \nAnswer:
                                                              \nThe balanced chemical equation is
                                                              \n2C2<\/sub>H2<\/sub> + 5O2<\/sub> \u2192 4CO2<\/sub> + 2H2<\/sub>O
                                                              \n2 \u00d7 (2 \u00d7 12U + 2 \u00d7 lU) + 5 \u00d7 (2 \u00d7 16U) \u2192 4 \u00d7 (12U + 2 \u00d7 16U) + 2(2 \u00d7 1U + 16U)
                                                              \n52 g + 160g \u2192 176 g + 36 g
                                                              \n52 g of acetylene when burnt in air produces 176 g carbon dioxide.
                                                              \nThe amount of carbon dioxide produced when 104 g acetylene burnt
                                                              \n\"AP<\/p>\n

                                                              At S.T.P. 1 gram molar mass of any gas occupies 22.4 litres.
                                                              \nSo 44g carbon dioxide occupies 22.4 litres volume.
                                                              \nThe volume occupied by 352 g carbon dioxide = \\(\\frac{352}{44}\\) \u00d7 22.4 = 8 \u00d7 22.4 = 179.2 litres.
                                                              \n44 g of carbon dioxide i.e., 1 mole of CO2<\/sub> contains 6.02 \u00d7 1023<\/sup> molecules. So the number of molecules present in 352 g of carbon dioxide
                                                              \n352
                                                              \n= \\(\\frac{352}{44}\\) \u00d7 6.02 \u00d7 1023<\/sup> = 8 \u00d7 6.02 \u00d7 1023<\/sup>
                                                              \n= 4.816 \u00d7 1024<\/sup> molecules.<\/p>\n","protected":false},"excerpt":{"rendered":"

                                                              AP State Syllabus AP Board 9th Class Physical Science Important Questions Chapter 6 Chemical Reactions and Equations AP State Syllabus 9th Class Physical Science Important Questions 6th Lesson Chemical Reactions and Equations 9th Class Physical Science6th Lesson Chemical Reactions and Equations 1 Mark Important Questions and Answers Question 1. Fe2O3 + 2 Al \u2192 Al2O3 …<\/p>\n","protected":false},"author":4,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"spay_email":""},"categories":[5],"tags":[],"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/apboardsolutions.guru\/wp-json\/wp\/v2\/posts\/8726"}],"collection":[{"href":"https:\/\/apboardsolutions.guru\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/apboardsolutions.guru\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/apboardsolutions.guru\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/apboardsolutions.guru\/wp-json\/wp\/v2\/comments?post=8726"}],"version-history":[{"count":1,"href":"https:\/\/apboardsolutions.guru\/wp-json\/wp\/v2\/posts\/8726\/revisions"}],"predecessor-version":[{"id":36457,"href":"https:\/\/apboardsolutions.guru\/wp-json\/wp\/v2\/posts\/8726\/revisions\/36457"}],"wp:attachment":[{"href":"https:\/\/apboardsolutions.guru\/wp-json\/wp\/v2\/media?parent=8726"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/apboardsolutions.guru\/wp-json\/wp\/v2\/categories?post=8726"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/apboardsolutions.guru\/wp-json\/wp\/v2\/tags?post=8726"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}