Short Answer Questions - II- 3 Marks

 Q. 1. Write the cations and anions present (if any) in the following compounds:
(a) CH₃COONa                        (b) NaCI
(c) H₂                                                  (d) NH₄NO₃

Ans. Anions                    Cations
     (a) CH₃COO^-        Na⁺
     (b) Cl^-                   Na⁺   
     (c) H₂ - It is a covalent compound
     (d)

Q. 2. Calculate the mass percentage of oxygen present in the following compounds and state the law of chemical combination associated. Given, H = 1, O = 16.

(i) Water (H₂O) and (ii) Hydrogen peroxide (H₂O₂)

Ans. According to Law of multiple proportions

       (i) H₂O, % of O =

       (ii) H₂0₂, % of O =

Q.3. Classify each of the following on the basis of their atomicity.
      (a) F₂                      (b) NO₂                              (d) C₂H₆
      (e) CO                    (f) H₂O₂                       (g) P₄O₁₀           (h) O₃
      (i) HCI                   (j) CH₄                           (k) He                (l) Ag

Ans. (a) 2                    (b) 3                             (c) 4                    (d) 8
         (e) 2                    (f) 4                             (g) 14                  (h) 3
         (i) 2                     (j) 5                                         
         (k) 1 (Noble gases do not combine and exist as monoatomic gases)

(l) Polyatomic: It is difficuIt to talk about the atomicity of metals as any measurable quantity will contain millions of atoms bound by metallic bond.

Q.4. Calculate the molecular mass of the following:
(a) H₂CO₃                     (b) C₂H₅OH                  (c) MgSO₄

Ans. (a) Molecular mass of H₂CO₃ = 2 x 1 + 1 x 12 + 3 x 16
                                                           = 2 + 12 + 48
                                                           = 62 u

(b) Molecular mass of C₂H₅OH = 2 x 12 + 5 x 1 + 1 x 16 + 1
                                                        = 24 + 5 + 16 + 1
                                                        = 46 u

(c) Molecular mass of MgSO4   = 1 x 24 + 1 x 32 + 4 x 16
                                                        = 24 + 32 + 64
                                                        = 120 u

Q.5. What are ionic and molecular compounds? Give examples.

Ans. Atoms of different elements join together in definite proportions to form molecules of compounds. For example, water, ammonia, carbon dioxide. Compounds composed of metals and non-metals contain charged species. The charged species are known as ions. An ion is a charged particle and can be negatively or positively charged. A negatively charged ion is called an anion and the positively charged ion is called cation. For example, sodium chloride, calcium oxide.

Q.6. Give three significance of mole.

Ans. (a) One mole represents 6.022 ×  10²³ ntities of a substance.
         (b) One mole of an element contains 6.022 × 10²³ atoms of the element.
         (c) One mole of a substance represents one gram formula mass of the substance.

Q.7. How many (a) molecules (b) hydrogen atoms (c) oxygen atoms are there in 0.5 mol of water?
Ans. (a) 1 mol of water contains 6.022 × 10²³ molecules

                ∴     0.5 mol of water contains                                                  

                                                           = 3.011 x 10²³ molecules

        (b) 1 molecule of water contains 2 atoms of hydrogen
              1 mol of water contains 2 × 6.022 × 10²³ atoms of hydrogen

               ∴     0.5 mol of water contains  atoms of hydrogen

                                                                 = 6.022 × 10²³ atoms of hydrogen

        (c) 1 molecule of water contains 1 atom of oxygen
             1 mol of water contains 6.022 x 10²³ atoms of oxygen
               ∴     0.5 mol of water contains  atoms of oxygen

Q.8. Calculate the number of moles present in:
(i) 3.011 x 10²³ number of oxygen atoms.
(ii) 60 g of calcium
      [Given that atomic mass of Ca = 40 u, Avogadro No. = 6.022 × 10²³]

Ans. (i) 1 mole of oxygen contains 6.022 x 10²³ atoms
               ∴     6.022 x 10²³ atoms of oxygen = 1 mol
              1 atom of oxygen =

               ∴     3.01 1 x 10²³ atoms of oxygen =

                                                                            = 0.5 mol

        (ii) Atomic mass of Ca = 40 u
             40g of calcium = 1 mol
             60g of calcium =   mol = 1.5 mol

Q.9. Calculate the mass per cent of each element of sodium chloride in one mole of it.

Ans. Molecular mass of NaCl = (1 x 23 + 1 x 35.5) u = 58.5 u
         Atomic mass of sodium = 23 u
        Mass per cent of Na =

                                           

       Mass % of Na = 39.32 %
       Atomic mass of chlorine = 35.5 u

       Mass % of Cl =

                             

Q. 10. Calculate the number of particles in each of the following:
(a) 46 g of Na atom
(b) 8 g of O₂ molecules
(c) 0.1 moles of carbon atom

Ans. (a) No. of moles of sodium =   = 2 moles
              We know that one mole of sodium contains 6.022 x 10²³ atoms.

                 ∴    2 moles of sodium contain = 2 x 6.022 x 10²³ atoms
                                                                      = 1.204 x 10²⁴ atoms
         (b) 1 mole of oxygen = 32 g
               32 g of O₂ contains 6.022 x 10²³ molecules

                 ∴    8 g of O₂ contains =

                                                       = 1.51 x 10²³ molecules

         (c) 1 mole of carbon atoms contains 6.022 × 1023 atoms
                 ∴    0.1 mole of carbon atoms contains = 6.022 x 1023 x 0.1 atoms

                                                                                     = 6.022 x 10²² atoms

Q. 11. Raunak took 5 moles of carbon atoms in a container and Krish also took 5 moles of sodium atoms in another container of same weight.
(a) Whose container is heavier?
(b) Whose container has more number of atoms?

Ans. (a) Mass of sodium atoms carried by Krish = (5 x 23) g = 115 g             

               Mass of carbon atoms carried by Raunak = (5 × 12) g = 60 g          

               Thus, Krish's container is heavier.       

         (b) Both the bags have same number of atoms as they have same number of moles of atoms.