(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 \(...
Question 1 Report
(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 \( \mathrm{Na_2S_2O_2} \).
(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) \( \mathrm{I_{2(s)} \to I_{2(g)}} \)
(ii) \( \mathrm{Cl_{(g)} + e^- \to Cl^-_{(g)}} \)
(f) State the effect of each of the following aqueous solutions on litmus paper: (i) \( \mathrm{Na_2SO_{4(aq)}} \) (ii) \( \mathrm{AlCl_{3(aq)}} \)
(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 \( \mathrm{C\ mol^{-1}} \)]
Answer Details
(a)(i) An ionic (electrovalent) bond is the electrostatic force of attraction between oppositely charged ions formed by the complete transfer of one or more electrons from a metal atom to a non-metal atom.
(ii) I. Magnesium oxide (MgO): ionic (electrovalent) bond. II. Ammonium ion (NH4+): covalent bonds, one of which is a coordinate (dative) covalent bond from N to the extra H+.
(b) Oxidation number of sulphur in sodium thiosulphate, Na2S2O3
\[ 2(+1)+2(S)+3(-2)=0 \Rightarrow 2S=+4 \Rightarrow S=+2 \](Average oxidation number of S = +2. If the formula is read strictly as Na2S2O2, the same method gives S = +1.)
(c) Faraday's first law: The mass of a substance liberated or deposited at an electrode during electrolysis is directly proportional to the quantity of electricity (charge) passed through the electrolyte.
(d)(i) Acid salt: sodium hydrogentrioxocarbonate(IV), NaHCO3 (or NaHSO4). (ii) Basic salt: magnesium hydroxychloride, Mg(OH)Cl (or basic lead carbonate).
(e)(i) I2(s) → I2(g): sublimation, energy is absorbed (endothermic, enthalpy of sublimation). (ii) Cl(g) + e- → Cl-(g): energy is released (exothermic, electron affinity/electron gain enthalpy).
(f)(i) Na2SO4(aq): neutral salt, no effect on litmus. (ii) AlCl3(aq): acidic (salt hydrolyses), turns blue litmus red.
(g) Efflorescence is the process by which a hydrated crystalline substance loses its water of crystallization to the atmosphere on exposure to air, becoming powdery.
(h) Two uses of activated charcoal: as an adsorbent to decolourize/purify (e.g. sugar solutions, water); in gas masks to adsorb poisonous gases.
(i) (i) Hydrogenation of vegetable oil: manufacture of margarine (solid cooking fats). (ii) Cracking: production of petrol and of alkenes for making plastics. (iii) Esterification: manufacture of esters used as flavourings, perfumes and solvents.
(j) Silver deposited (Ag+ + e- → Ag, so 1 mol needs 96500 C):
\[ n(\text{Ag})=\frac{Q}{F}=\frac{10920}{96500}=0.113\ \text{mol} \]Download The App On Google Playstore
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