{"id":8584,"date":"2023-11-05T21:14:52","date_gmt":"2023-11-05T15:44:52","guid":{"rendered":"https:\/\/apboardsolutions.guru\/?p=8584"},"modified":"2023-11-10T16:48:11","modified_gmt":"2023-11-10T11:18:11","slug":"ap-board-9th-class-physical-science-important-questions-chapter-4","status":"publish","type":"post","link":"https:\/\/apboardsolutions.guru\/ap-board-9th-class-physical-science-important-questions-chapter-4\/","title":{"rendered":"AP Board 9th Class Physical Science Important Questions Chapter 4 Atoms and Molecules"},"content":{"rendered":"

AP State Syllabus AP Board 9th Class Physical Science Important Questions<\/a> Chapter 4 Atoms and Molecules<\/p>\n

AP State Syllabus 9th Class Physical Science Important Questions 4th Lesson Atoms and Molecules<\/h2>\n

9th Class Physical Science 4th Lesson Atoms and Molecules 1 Mark Important Questions and Answers<\/h3>\n

Question 1.
\nWhat is the difference between 2N and N2<\/sub>?
\nAnswer:
\n2N means two nitrogen atoms.
\nN2<\/sub> means one nitrogen molecule.<\/p>\n

Question 2.
\nMohan said, “O2<\/sub> differs from O,”. Do you agree? Justify.
\nAnswer:
\n1) Yes, I agree with Mohan’s statement.
\n2) ‘O’ means single oxygen atom.
\n‘O2<\/sub>‘ means single oxygen molecule.<\/p>\n

\"AP<\/p>\n

Question 3.
\nThe atomic number (Z) of an element is 6. Name the element.
\nAnswer:
\nCarbon.<\/p>\n

Question 4.
\nWrite any one precaution in doing the experiment chromotography.
\nAnswer:
\nMake sure that the ink line or mark does not touch the water.<\/p>\n

Question 5.
\nIn a class, a teacher asked students to write the molecular formula of Oxygen, Namitha wrote the formula as “O2<\/sub>“, Raju as “O”. Which one is correct?
\nAnswer:
\nNamitha is correct.
\nMolecular formula of oxygen is O2<\/sub>.<\/p>\n

9th Class Physical Science 4th Lesson Atoms and Molecules 2 Marks Important Questions and Answers<\/h3>\n

Question 1.
\nFill the following table.<\/p>\n\n\n\n\n\n\n\n
Name<\/td>\nMolecular Mass<\/td>\nNo. of Particles present in molar mass<\/td>\n<\/tr>\n
1. Atomic Oxygen<\/td>\n16 gr<\/td>\n<\/td>\n<\/tr>\n
2. Sodium<\/td>\n23 gr<\/td>\n<\/td>\n<\/tr>\n
3. Sodium chloride<\/td>\n<\/td>\n6.02 \u00d7 1023<\/sup> of Sodium chloride<\/td>\n<\/tr>\n
4. Water<\/td>\n18 gr<\/td>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Answer:<\/p>\n\n\n\n\n\n\n\n
Name<\/td>\nMolecular Mass<\/td>\nNo. of Particles present in molar mass<\/td>\n<\/tr>\n
1. Atomic Oxygen<\/td>\n16 gr<\/td>\n6.02 \u00d7 1023<\/sup> of oxygen atoms<\/td>\n<\/tr>\n
2. Sodium<\/td>\n23 gr<\/td>\n6.02 \u00d7 1023<\/sup> of sodium atoms<\/td>\n<\/tr>\n
3. Sodium chloride<\/td>\n58.5 gr<\/td>\n6.02 \u00d7 1023<\/sup> of Sodium chloride<\/td>\n<\/tr>\n
4. Water<\/td>\n18 gr<\/td>\n6.02 \u00d7 1023<\/sup> of water molecules<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Question 2.
\nCompare the subatomic particles electron, proton and neutron.
\nAnswer:
\n\"AP<\/p>\n

Question 3.
\nWhat are the materials used in “Conservation of mass” experiment?
\nAnswer:
\nMaterial required for Conservation of mass:
\nSodium sulphate, Barium chloride, distilled water, conical flask, spring balance, small test tube, rubber cork, thread, retort stand.<\/p>\n

9th Class Physical Science 4th Lesson Atoms and Molecules 4 Marks Important Questions and Answers<\/h3>\n

Question 1.
\nFill in the blanks in the table using the given information.
\n\"AP
\nAnswer:
\n\"AP<\/p>\n

Question 2.
\nRead the following information and answer.
\nMolecular mass of a molecule is the sum of the atomic masses of individual atoms in it.<\/p>\n\n\n\n\n\n\n\n
Element<\/td>\nAtomic number<\/td>\nAtomic mass<\/td>\n<\/tr>\n
Sodium<\/td>\n11<\/td>\n23<\/td>\n<\/tr>\n
Oxygen<\/td>\n8<\/td>\n16<\/td>\n<\/tr>\n
Hydrogen<\/td>\n1<\/td>\n1<\/td>\n<\/tr>\n
Carbon<\/td>\n6<\/td>\n12<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

i) Find the molecular mass of Na2<\/sub>CO3<\/sub>.
\nAnswer:
\nMolecular mass of Na2<\/sub>CO3<\/sub> = (23 \u00d7 2) + 12 + (16 \u00d7 3) = 46 + 12 + 48 = 106<\/p>\n

ii) If the molecular weight of a compound is 44. Which is made with carbon and oxygen. What its molecular formula?
\nAnswer:
\nMolecular weight of a compound = 44
\nAt. mass of Carbon = 12 Remaining at. mass = 44-12 = 32 = 16 \u00d7 2
\nHence, 16 \u00d7 2 \u21d2 (Oxygen atomic mass \u00d7 2) \u21d2 O2<\/sub>
\nMolecular formula = CO2<\/sub><\/p>\n

iii) What is the unit of atomic mass?
\nAnswer:
\nUnit of atomic mass = amu
\natomic mass unit (amu) is defined as precisely \\(\\frac{1}{12}\\) the mass of an atom of carbon -12.<\/p>\n

iv) On the basis of molecular weights of NaOH and H2<\/sub>O, which is heavier?
\nAnswer:
\nMolecular weight of NaOH = 23+16 + 1= 40
\nMolecular weight of H2<\/sub>O = (1 \u00d7 2)+ 16 = 2 + 16=18
\nHence, NaOH is heavier than H2<\/sub>O.<\/p>\n

Question 3.
\nComplete the table.
\n\"AP
\nAnswer:
\n\"AP<\/p>\n

9th Class Physical Science 4th Lesson Atoms and Molecules Important Questions and Answers<\/h3>\n

9th Class Physical Science 4th Lesson Atoms and Molecules 1 Mark Important Questions and Answers<\/span><\/p>\n

Question 1.
\nHow did the element Helium get its name?
\nAnswer:
\nPlace of discovery of element can also play a role in its naming. The gas which was first discovered in the sun was named Helium. Because, Greek name for sun is helios’.<\/p>\n

Question 2.
\nWhat is an atom?
\nAnswer:
\nAn atom is the smallest particle of an element that can participate in chemical reaction and retain all its properties.<\/p>\n

\"AP<\/p>\n

Question 3.
\nIs ‘Na’ an element or compound? Why?
\nAnswer:
\n‘Na’ is an element, because it was formed by the same atoms of ‘Na’.<\/p>\n

Question 4.
\nIs O2<\/sub> an element or compound? Why?
\nAnswer:
\nO2<\/sub> is a compound, because O2<\/sub> is formed by combining two oxygen atoms.<\/p>\n

Question 5.
\nWhat is an Avogadro number? What is its value?
\nAnswer:
\nThe number of particles present in one mole of any substance is the Avogadro number (NA<\/sub>).
\nThis is equal to 6.022 \u00d7 1023<\/sup>.<\/p>\n

Question 6.
\nWhich instrument is used to calculate the atomic mass exactly?
\nAnswer:
\nMass spectrometer.<\/p>\n

\"AP<\/p>\n

Question 7.
\nWhat is atomic mass?
\nAnswer:
\nThe number of times one atom of given element is heavier than 1\/12th part of atomic mass of carbon -12 is called its atomic mass.<\/p>\n

Question 8.
\nHow molecules are formed?
\nAnswer:
\nA molecule is formed by the combination of different kinds of atoms that are chemically bonded together by attractive forces.<\/p>\n

Question 9.
\nWhy is it not possible to see an atom with naked eye?
\nAnswer:
\nThe size of an atom is so small i.e., less than 1 nm (1 nano metre). So we are unable to see an atom.<\/p>\n

Question 10.
\nWhat is a chemical formula?
\nAnswer:
\nThe chemical formula of a compound is a symbolic representation of its composition.<\/p>\n

Question 11.
\nHow many atoms are present in.
\ni) H2<\/sub>S molecule and
\nii) PO4<\/sub>3-<\/sup> ion?
\nAnswer:
\ni) The number of atoms in H2<\/sub>S molecule = 2 + 1=3
\nii) The number of atoms in PO4<\/sub>3-<\/sup> ion =1 + 4 = 5<\/p>\n

9th Class Physical Science 4th Lesson Atoms and Molecules 2 Marks Important Questions and Answers<\/span><\/p>\n

Question 1.
\nWho is called as the father of modern chemistry? What are his main contributions?
\nAnswer:<\/p>\n

    \n
  1. Antoine Lavoisier a French scientist is called as “Father of modern chemistry”.<\/li>\n
  2. He made many important contributions to chemistry.<\/li>\n
  3. One of his contributions is law of conservation of mass.<\/li>\n<\/ol>\n

    Question 2.
    \nState the following.
    \na) Law of conservation of mass
    \nb) Law of constant proportions
    \nAnswer:
    \na) Law of conservation of mass :
    \nMatter is neither created nor destroyed during a chemical reaction.
    \n(or)
    \nThe mass of the reactants is equal to the mass of the products of chemical reaction.<\/p>\n

    b) Law of constant proportions :
    \nA given chemical substance always contains the same elements combined in a fixed proportions by weight.<\/p>\n

    \"AP<\/p>\n

    Question 3.
    \nWhat are the Dalton’s proposals about the nature of matter?
    \nAnswer:
    \nJohn Dalton proposed the basic theory about the nature of matter. His proposals are :<\/p>\n

      \n
    1. If mass was to be conserved, then all elements must be made up of extremely small particles called atoms.<\/li>\n
    2. If law of constant proportions is to be followed, the particles of same substance couldn’t be dissimilar.<\/li>\n<\/ol>\n

      Question 4.
      \nWhat is the proposal of Indian sage Kanada, about atom?
      \nAnswer:<\/p>\n

        \n
      1. About 2600 years ago, an Indian sage called Kanada, postulated atoms in his Vaishesika sutra”.<\/li>\n
      2. He proposed that all forms of matter are composed of very small particles known as “Anu”.<\/li>\n
      3. Each “Anu” may be made up of still smaller particles called “Paramanu”.<\/li>\n<\/ol>\n

        Question 5.
        \nWhat is the use of symbols for elements?
        \nAnswer:<\/p>\n

          \n
        1. We know that chemistry involves a lot of reactions.<\/li>\n
        2. It will be a waste of time to write the full name of the elements and compounds every time to describe a reaction.<\/li>\n
        3. To avoid this we use symbols for naming the elements and formulae to represent compounds.<\/li>\n<\/ol>\n

          Question 6.
          \nWhat are the characteristics of a symbol?
          \nAnswer:
          \n1) A symbol can have either one or two letters of English.
          \nEx : H, He, N, Ne, etc.<\/p>\n

          2) The first letter of the symbol is always upper case and the second letter is always lower case.
          \nEx :
          \n1) Al, Cr, Cl, etc. is the right method to represent elements.
          \n2) CL, bE, he, etc. is the wrong method to represent elements.<\/p>\n

          \"AP<\/p>\n

          Question 7.
          \nIn a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g of water, and 8.2 g of sodium ethanoate. Show that these observations are in agreement with law of conservation of mass.
          \nAnswer:
          \nSodium carbonate + Ethanoic acid \u2192 Sodium ethanoate + Carbon dioxide + Water
          \nThe total mass of reactants = 5.3 + 6 = 11.3 g
          \nThe total mass of products = 2.2 + 0.9 + 8.2 = 11.3 g
          \n\u2234 Total mass of reactants = Total mass of products
          \nSo these observations are in agreement with law of conservation of mass.<\/p>\n

          Question 8.
          \nHydrogen and oxygen combine in the ratio of 1 : 8 by mass to form water. What mass of oxygen gas would be required to react completely with 3 g of hydrogen gas?
          \nAnswer:
          \nAccording to data 1 g of hydrogen is reacting with 8 g of oxygen.
          \nSo amount of oxygen would be required to react completely with 3 g of hydrogen
          \n= 3 x 8 = 24 g<\/p>\n

          Question 9.
          \nCalculate formula unit weight of ZnO, Na2<\/sub>O, K2<\/sub>CO3<\/sub> (Given atomic weight of Zn = 654)
          \nAnswer:
          \nFormula unit weight of ZnO = 65 + 16 = 81 u
          \nFormula unit weight of Na2<\/sub>O = 2 \u00d7 23 +16 = 62u
          \nFormula unit weight of K2<\/sub>CO3<\/sub> = 2 \u00d7 39 + 12 + 3 \u00d7 16 = 138 u<\/p>\n

          Question 10.
          \nCalculate the number of moles for the following.
          \ni) 52 g of He (finding mole from mass).
          \nii) 12.044 \u00d7 1023<\/sub> number of He atoms (finding mole from number of particles).
          \nAnswer:
          \n\"AP<\/p>\n

          Question 11.
          \nIf one mole of carbon atom weighs 12 g. What is the mass of 1 atom of carbon?
          \nAnswer:
          \n\"AP<\/p>\n

          Question 12.
          \nWhen 3 g of carbon is burnt in 8 g of oxygen 11 g of carbon dioxide is produced. What mass of carbon dioxide is formed when 3 g of carbon is burnt in 50 g of oxygen.
          \nAnswer:
          \n3 g of carbon react with 8 g of oxygen to form 11 g of carbon dioxide.
          \nRatio of carbon and oxygen = 3 : 8
          \nThe amount oxygen react with 3g of carbon = 3 \u00d7 8 = 24.
          \nSo the amount of carbon dioxide formed = 3 + 24 = 27 g.<\/p>\n

          \"AP<\/p>\n

          Question 13.
          \nGiven the names of the elements present in the following compounds.
          \na) Quick lime
          \nb) Hydrogen bromide
          \nc) Baking soda
          \nd) Potassium sulphate
          \nAnswer:<\/p>\n\n\n\n\n\n\n\n
          Compound<\/td>\nFormula<\/td>\nElements<\/td>\n<\/tr>\n
          a) Quick lime<\/td>\nCaO<\/td>\nCalcium, oxygen<\/td>\n<\/tr>\n
          b) Hydrogen bromide<\/td>\nHB2<\/sub><\/td>\nHydrogen, bromine<\/td>\n<\/tr>\n
          c) Baking soda<\/td>\nNaHCO3<\/sub><\/td>\nSodium, hydrogen, carbon, oxygen<\/td>\n<\/tr>\n
          d) Potassium sulphate<\/td>\nK2<\/sub>SO4<\/sub><\/td>\nPotassium, sulphur, oxygen<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

          Question 14.
          \nCalculate number of sulphur (Sg) present in 16 g of solid sulphur.
          \nAnswer:
          \nMolecular weight of sulphur = 8 \u00d7 32 = 256 g.
          \n256 g of sulphur contains 6.022 \u00d7 1023<\/sub> molecules.
          \nNumber of molecules present in 16 g of sulphur = \\(\\frac{16}{256}\\) \u00d7 6.022 \u00d7 1023<\/sup>
          \n= 3.77 \u00d7 1022<\/sup> molecules<\/p>\n

          Question 15.
          \nAnitha wrote the formula for oxygen molecule as 20. Is it correct or not? Why?
          \nAnswer:<\/p>\n

            \n
          1. It is not correct.<\/li>\n
          2. The formula of oxygen molecule is O2<\/sub>.<\/li>\n
          3. 2O shows two separate atoms of oxygen.<\/li>\n
          4. O2<\/sub> shows molecule of oxygen.<\/li>\n<\/ol>\n

            9th Class Physical Science 4th Lesson Atoms and Molecules 4 Marks Important Questions and Answers<\/span><\/p>\n

            Question 1.
            \nHow elements got their names? Explain with examples.
            \nAnswer:
            \nI: Sometimes elements are named based on their property.
            \nEx :
            \n1) The Latin name for water is “hydro”.
            \nSo the element that combined with oxygen to give water was named as ‘hydrogen’.<\/p>\n

            2) The Latin word for acid is ‘oxy’.
            \nHence the gas that forms acid is ‘oxygen’.<\/p>\n

            II. Place of discovery of element can also play a role in its naming.
            \nEx : The gas that was first discovered in the sun (Greek name for the sun is “helios”) was named as ‘helium’.<\/p>\n

            III. Sometimes the elements were named to honour the scientists.
            \nEx : Einsteinium, Fermium, Rutherfordium and Mendelevium, etc.<\/p>\n

            \"AP<\/p>\n

            Question 2.
            \nDefine the following terms.
            \na) Atomicity
            \nb) Valency
            \nc) Ions
            \nAnswer:
            \na) Atomicity :
            \nThe number of atoms constituting a molecule is known as its atomicity.<\/p>\n

            Ex :
            \n1) Na is monoatomic
            \n2) O2<\/sub> is diatomic
            \n3) O3<\/sub> is triatomic<\/p>\n

            b) Valency :
            \nAtoms of the elements have power to combine with atoms of other elements. This is known as valency.
            \nEx :
            \n1) Valency of carbon is 4.
            \n2) Valency of oxygen is 2.
            \n3) Valency of hydrogen is 1.<\/p>\n

            c) Ions:
            \n1) Ions may be a single charged atoms or a group of atoms that have a net charge on them.
            \n2) A negatively charged ion is called anion and the positive charge ion is cation.
            \nEx : Na+<\/sup>, Cu+2<\/sup>, S2-<\/sup>, N3-<\/sup>, etc.<\/p>\n

            Question 3.
            \nExplain the method of writing a formula to a compound using criss – cross method, with the help of an example.
            \nAnswer:
            \nThe following steps should be taken while attempting to write a chemical formula using criss – cross method.
            \nEx : Take sodium carbonate as an example.
            \n1) Write the symbols of atoms or group of atoms side by side, usually the cation first.
            \nNaCO3<\/sub><\/p>\n

            2) Write the valency of each atom or group of atoms on the top of its symbol.
            \nNa\u00b9 (CO3<\/sub>)\u00b2<\/p>\n

            3) Divide the valency number by their highest common factor if any to get the simple ratio.
            \nNa\u00b9 (CO3<\/sub>)\u00b2<\/p>\n

            4) Interchange the valency and write the numbers to the lower right of the constituents as subscript.
            \nNa2<\/sub>(CO3<\/sub>)1<\/sub><\/p>\n

            5) If any constituent receives the number 1, ignore it while writing the formula.
            \nNa2<\/sub>CO3<\/sub><\/p>\n

            6) If group of atoms received the number more than 1, enclose it within brackets. Hence the formula for the sodium carbonate is Na2<\/sub>CO3<\/sub>.<\/p>\n

            Question 4.
            \nDefine the terms :
            \na) molecular mass,
            \nb) formula unit mass,
            \nc) mole and
            \nd) molar mass.
            \nAnswer:
            \na) Molecular mass :
            \nThe molecular mass of a substance is the sum of the atomic masses of all the atoms in a molecule of a substance.<\/p>\n

            b) Formula unit mass :
            \nThe formula unit mass of a substance is a sum of the atomic masses of all atoms in a formula unit of a compound.<\/p>\n

            c) Mole :
            \n1) One mole of a substance is the amount of the substance which contains as many particles or entities that are equal to the atoms present in exactly 12 grams of C12<\/sup> isotope.
            \n2) The number of particles present in one mole of any substance has a fixed value of 6.022 \u00d7 1023<\/sup>. This number is called Avogadro’s constant (NA<\/sub>).<\/p>\n

            d) Molar mass :
            \nThe mass of 1 mole of a substance which is expressed in grams is called its molar mass.<\/p>\n

            \"AP<\/p>\n

            Question 5.
            \nWhat are the main postulates of Dalton’s atomic theory?
            \nAnswer:
            \nThe main postulates of Dalton\u2019s atomic theory are :<\/p>\n

              \n
            1. Matter consists of indivisible particles called atoms.<\/li>\n
            2. Atoms are neither created nor destroyed in a chemical reaction, but atoms will reorganize.<\/li>\n
            3. All the atoms of a given element have identical mass and chemical properties.<\/li>\n
            4. Atoms of different elements have different masses and chemical properties.<\/li>\n
            5. Compounds are formed when atoms of different elements combine in simple whole number ratios i.e., chemical change is the union or separation of atoms as a whole number.<\/li>\n<\/ol>\n

              Question 6.
              \nDraw the pie diagram to understand the atomic mass and explain it.
              \nAnswer:
              \n\"AP
              \nExplanation :<\/p>\n

                \n
              1. Let us assume the circle in the diagram represents mass of one carbon – 12.<\/li>\n
              2. It is divided into 12 equal parts as shown in the figure.<\/li>\n
              3. Each part represents 1\/12th of atomic mass of one carbon -12.<\/li>\n<\/ol>\n

                Atomic mass unit :
                \nOne atomic mass unit is defined as the mass exactly one-twelfth the atomic mass of carbon – 12 isotope.<\/p>\n

                Question 7.
                \nIllustrate the concept of mole through a diagram.
                \nAnswer:
                \nMole :<\/p>\n

                  \n
                1. One mole of a substance is the amount of the substance which contains as many particles (atoms, molecules etc.) or entities that are equal to the atoms present in exactly 12 grams of 12<\/sup>C isotope.<\/li>\n
                2. The number of particles present in one mole of any substance has a fixed value of 6.022 \u00d7 1023<\/sup>. This number is called Avogadro’s constant (NA<\/sub>).<\/li>\n<\/ol>\n

                  \"AP<\/p>\n

                  Question 8.
                  \nHow can you appreciate John Dalton for proposing his atomic theory?
                  \nAnswer:<\/p>\n

                    \n
                  • We know, development of science and technology is a combined effort of Roman scientists.<\/li>\n
                  • The zeal to know or discover something new, leads the scientists for their discoveries.<\/li>\n
                  • One of such is the atomic theory proposed by Dalton, based on Lavoisier’s law of conservation of mass and Proust’s law of constant proportions.<\/li>\n
                  • Dalton said atom is indivisible.<\/li>\n
                  • This proposal lead to discover many new things by various scientists and to unveil the complete structure of atom.<\/li>\n
                  • Hence Dalton’s contribution is highly appreciable.<\/li>\n<\/ul>\n

                    Question 9.
                    \nHow do you feel after studying the symbols and formulae of different elements and compounds?
                    \nAnswer:<\/p>\n

                      \n
                    • In my earlier class I came to know that chemistry is nowhere but in our kitchen.<\/li>\n
                    • I used to call so many chemicals with their names.<\/li>\n
                    • Now I am able to call them with their symbols and formulae.<\/li>\n
                    • For example 1 can call the common salt as NaCl.<\/li>\n
                    • This thrills me alot, and I am curious to know the formulae of so many common household substances.<\/li>\n
                    • This is very helpful for my higher studies.<\/li>\n<\/ul>\n

                      \"AP<\/p>\n

                      Question 10.
                      \nDescribe the experiment conducted by Joseph L. Proust, which lead him to propose law of constant proportions.
                      \nAnswer:<\/p>\n

                        \n
                      • Proust took two samples of copper carbonate, one from nature and another prepared in the lab.<\/li>\n
                      • These two samples are chemically decomposed to find percentage of copper, carbon and oxygen.<\/li>\n
                      • The results obtained are given in the table.<\/li>\n<\/ul>\n\n\n\n\n\n\n
                        Weight percentage of<\/td>\nNatural sample<\/td>\nSynthetic sample<\/td>\n<\/tr>\n
                        Copper<\/td>\n51.35<\/td>\n51.35<\/td>\n<\/tr>\n
                        Carbon<\/td>\n38.91<\/td>\n38.91<\/td>\n<\/tr>\n
                        Oxygen<\/td>\n9.74<\/td>\n9.74<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
                          \n
                        • From the above table we observe that the percentage of copper, carbon and oxygen atoms in two samples are same.<\/li>\n
                        • Based on this observation Proust proposed the law of constant proportions as “A given chemical substance always contains the same elements combined in a fixed proportions by weight”.<\/li>\n<\/ul>\n

                          Question 11.
                          \nWrite down the formulae of these compounds, using criss – cross method?
                          \ni) Sodium oxide
                          \nii) Aluminium chloride
                          \niii) Sodium sulphate
                          \niv) Magnesium hydroxide
                          \nAnswer:
                          \n\"AP<\/p>\n

                          Question 12.
                          \nWrite down the names of compounds represented by the following formulae and also write the anion, cation.
                          \ni) Al2<\/sub>(SO4<\/sub>)3<\/sub>
                          \nii) CaCl2<\/sub>
                          \niii) K2<\/sub>SO4<\/sub>
                          \niv) KNO3<\/sub>
                          \nv) CaCO3<\/sub>
                          \nAnswer:
                          \n\"AP<\/p>\n

                          Question 13.
                          \nWhat are the rules you have to follow while writing a chemical formula?
                          \nAnswer:<\/p>\n

                            \n
                          1. The valencies or charges on the ion must balance.<\/li>\n
                          2. When a compound consists of metal and non-metal, the name of the symbol of metal is written first, eg : Calcium oxide (CaO)<\/li>\n
                          3. In compounds formed with poly atomic ions, the ion is enclosed in a bracket before writing the number to indicate the ratio.<\/li>\n<\/ol>\n

                            Question 14.
                            \nCalculate the molecular weight H2<\/sub>, O2<\/sub>, Cl2<\/sub>, CO2<\/sub>, CH4<\/sub>, C2<\/sub>H6<\/sub>, C2<\/sub>H4<\/sub>, NH3<\/sub>, CH3<\/sub>OH.
                            \nAnswer:
                            \nMolecular weight of H2<\/sub> = 2 \u00d7 1 = 2 u
                            \nMolecular weight of O2<\/sub> = 2 \u00d7 16 = 32 u
                            \nMolecular weight of Cl2<\/sub> = 2 \u00d7 35.5 = 71 U
                            \nMolecular weight of CO2<\/sub> = 12 + 2 \u00d7 16 = 44 u
                            \nMolecular weight of CH4<\/sub> = 12 + 4 \u00d7 1 = 16 u
                            \nMolecular weight of C2<\/sub>H6<\/sub> = 2 \u00d7 12 + 6 \u00d7 1= 30 u
                            \nMolecular weight of C2<\/sub>H4<\/sub> = 2 \u00d7 12 + 4 \u00d7 1= 28 u
                            \nMolecular weight of NH3<\/sub> = 14 + 3 \u00d7 1 = 17 u
                            \nMolecular weight of CH3<\/sub>OH = 12 + 4 \u00d7 1 + 16 = 32 u<\/p>\n

                            \"AP<\/p>\n

                            Question 15.
                            \na) What is atomicity?
                            \nb) Give examples.
                            \nc) Why do elements have different atomicities?
                            \nAnswer:
                            \na) Atomicity:
                            \nThe number of atoms constituting a molecule is known as its ‘atomicity’.<\/p>\n

                            b) Examples :
                            \nA molecule of hydrogen consists of two atoms of hydrogen. Here the atomocity is two. Hence it is known as a diatomic molecule. Helium (He), Argon (Ar) exist as single atom. Hence they are known as monoatomic.
                            \nOzone (O3<\/sub>) has tetratomic
                            \nSulphur (S8<\/sub>) has octatomic<\/p>\n

                            c) Every element has a definite combining capacity, that determines the atomicity of its molecules. Every element reacts with other element according to its combining capacity, which we call as its valency.<\/p>\n","protected":false},"excerpt":{"rendered":"

                            AP State Syllabus AP Board 9th Class Physical Science Important Questions Chapter 4 Atoms and Molecules AP State Syllabus 9th Class Physical Science Important Questions 4th Lesson Atoms and Molecules 9th Class Physical Science 4th Lesson Atoms and Molecules 1 Mark Important Questions and Answers Question 1. What is the difference between 2N and N2? …<\/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\/8584"}],"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=8584"}],"version-history":[{"count":1,"href":"https:\/\/apboardsolutions.guru\/wp-json\/wp\/v2\/posts\/8584\/revisions"}],"predecessor-version":[{"id":36459,"href":"https:\/\/apboardsolutions.guru\/wp-json\/wp\/v2\/posts\/8584\/revisions\/36459"}],"wp:attachment":[{"href":"https:\/\/apboardsolutions.guru\/wp-json\/wp\/v2\/media?parent=8584"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/apboardsolutions.guru\/wp-json\/wp\/v2\/categories?post=8584"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/apboardsolutions.guru\/wp-json\/wp\/v2\/tags?post=8584"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}