(a)(i) Define ionic bond.
(ii) What type of bond (s) exist (s) in: I. magnesium oxide; II. ammonium ion?
(b) Determine the oxidation number of sulphur in Na\(_2\)S\(_2\)O\(_2\).
(c) State Faraday’s first law.
(d) Give one example each of: (i) acid salt; (ii) base salt.
(e) Name the type of energy change that occurs in each of the following processes
(i) I\(_{2(s)}\) \(\to\) I\(_{2(g)}\)
(ii) Cl\(_{(g)}\) + e\(^{-}\) \(\to\) Cl\(^{-_(g)}\)
(f) State the effect of each of the following aqueous solutions on litmus paper: (i) Na\(_2\)SO\(_{4(aq)}\) (ii) AlCl\(_{3(aq)}\)
(g) Define the term efflorescence.
(h) Give two uses of activated charcoal.
(i) State one use of each of the following processes in the chemical industry: (i) hydrogenation of vegetable oil; (ii) cracking; (iii) esterification.
(j) Calculate the amount of silver deposited in moles when 10920 coulombs of electricity is passed through a solution of a silver salt. [ Faraday constant– 96500 C mol\(^{-1}\)]
Explanation
(a)(i) Ionic bond is the electrostatic force of attraction between oppositely charged ions/cations and anions.
OR
Ionic bond is defined as the type of bond that is formed from/ by/ through the transfer of electrons from one atom of an element (metal) to an atom of another (non - metal).
(ii) (I) – Ionic / electrovalent.
(II) – „Coordinate (Covalent) / dative.
(b) Oxidation number of sulphur in Na\(_2\)S\(_2\)O\(_2\);
2 x Na + 2 x S + 3 x 0 = 0
2 x 1 + 2s + 3(-2) = 0
2 + 2s – 6 = 0
2s = 4
s = +2
c) Farady's first law states that the mass of an element discharged during electrolysis is directly proportional to the of current passed.
(d)(i) NaHSO\(_4\), NaHCO\(_3\), KHSO\(_3\), etc. (ii) Mg(OH)Cl, Zn(OH)Cl, Zn(OH)NO\(_3\), etc.
e)(i) Sublimation energy. (ii) Electron affinity.
f) (i) Na\(_2\)SO\(_{4(aq)}\) No effect on litmus paper/Neutral to litmus.
(ii) AlCl\(_{3(aq)}\) —Turns blue litmus paper red/Acidic to litmus.
(g) Efflorescence: Loss of (all apart from) water of crystallization by a substance on exposure to the air/Atmosphere.
(h) Activated Charcoal: (i) To remove colouring matter. (ii) To absorb gases. (iii) To remove impurities from liquids. (iv) Whitening of teeth. (v) To remove scent/To decolourize.
(i)(i) Hydrogenaton of Vegetable Oil: Production of margarine/Hardening of oils.
(ii) Cracking: Increase the yield of petrol/Improves the quality of petrol to produce raw materials or petrochemicals.
(iii) Esterification: Production of akanoates. —as solvents for paints/gums/cellulose. —in perfumery. —in making cellulose acetate (for photographic films). —as flavouring agents.
j) Ag\(^{-}\) + eg\(^{-}\) \(\to\) Ag
96500c of electricity deposits I mole of Ag
10920c of electricity = \(\frac{10920 \times 1.0}{96500}\)
= 0.113moles
= 0.11 moles.