TNPSC - Atoms and Molecules - 10th Standard Science

1.      From the given examples, form the pair of isotopes and the pair of isobars: 18Ar40, 17CI35, 20Ca40, 17CI37    
          Answer:  Isotopes     :     17CI35, 17CI37   
                           Isobars       :      18Ar40, 20Ca40

2.       Molecular mass of Nitrogen is 28.  Its atomic mass is 14.  Find the atomicity of Nitrogen.   (SEP - 2014, APRIL – 2014, 12)
           Answer:  Atomicity   =   Molecular Mass
                                                          Atomic Mass
                                                =     28
                                                        14
                  Atomicity             =      2

3.      Gram molecular mass of oxygen is 32g/  Density of Oxygen is 1.42g/cc.  Find the gram molecular volume of Oxygen.
          Gram Molecular Volume    =    Gram Molar Mass
                                                                     Density
                                                          =         32
                                                                    1.429
          Gram Molecular Volume of Oxygen     =    22.4 litre

4.       ‘Cl’ represents chlorine atom, ‘CI₂’ represents chlorine molecule.   List our any two difference between atoms and molecules.
     Atom
  Molecule

1.  Atom is an non bonded entity.
1.  Molecule is a bonded entity.
2.  It may or may not exist freely.
Eg: CI
2.  It can exist freely.
  Eg: CI₂

5.      Calculate the gram molecular mass of water from the values of gram atomic mass of hydrogen and of Oxygen.  (APRIL – 2013,12)
          Gram atomic mass of hydrogen   =   1g
          Gram atomic mass of oxygen       =   16g
          Answer:   H₂O =  2[H] + 1[O]  
          Gram molecular mass of water   = 2[1] + 1[16]  =  2 + 16
          Gram molecular mass of water  =  18g

6.       One mole of any substance contains 6.023 ×1023 particles.
          If 3.0115  ×  1023 particles are present in CO₂.  Find the number of moles.
         Number of moles  =  No. Of molecules      
                                                 6.023 × 1023          
                                          =   3.0115 × 1023
                                                6.023 ×1023
                                                    =  0.5 moles

7.      ________ have equal number of neutrons.
         a. Isobars
         b. Isotones
         c. Isotopes
         d. Mass Numbers
         Answer:  b. Isotones

8.     Classify the following based on atomicity:
        a. Chlorine
        b. Neon
        c. Phosphorous
        d. Ozone
         Answer:    Chlorine             -       Diatomic Molecule
                           Neon                  -       Monotonic Molecule
                           Phosphorous      -       Polyatomic Molecule
                           Ozone                -       Triatomic Molecule

9.      Identify and correct the mistake in each of the following:
         a. The molar volume of gas at STP is 22.4 cm₃.
         b. 2 × R.M.M. = V.D
         c. An atom cannot exist independently.
         d. The ratio of atoms in a molecule may be integral or simple or may not be fixed.
        d. H₂O is a homo atomic molecule.
        Answer:  a. The molar volume of gas at STP is 22.4 Litre.
                        b. 2 × V.D. = R.M.M.
                        c. An atom may or may not exist independently.
                        d. The ratio of atoms in a molecule are intergral and  fixed.
                        d. H₂O  is a  Hetero atomic molecule.

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