a) Define the following in term:. of electron transfer: (i) oxidation; (ii) reduction. (b)(i) Determina the oxidation stale of phosphorus in each of the following structures: I. POCI\(_3\) II. PH\(_3\). (ii) State with reasons whether the following compounds will form acidic, neutral or basic aqueous solutions: I. NaNO\(_3\) II. Na\(_2\)H\(_4\)CI; Ill. Na\(_2\)CO\(_3\). (c) Consider the set-up
(i) What is the gas produced in the experiment illustrated by the set-up above? (ii) Name the method of collection of gas (iii) Give a reason for your answer in (c)(ii) above (iv) State the function of the concentrated H\(_2\)SO\(_4\) in the conical flask (v) Give of collection of the gas one I. physical property; II. chemical property of the gas (vi) State one chemical test to identify the gas. (d) A 4.3 g hydrated sodium tetraoxosulphate (VI) (Na\(_2\)SO\(_4\).xH\(_2\)O) was heated to remove the water of crystallization. The remaining anhydrous salt had a mass of 2.12 g. Calculate the value of x in the t I hydrated salt. [H = 1; O = 16; Na = 23; S = 32 ]
Explanation
(a)(i) Oxidation is the process of electron loss. Reduction is the process of electron gain (b)(i) POCI\(_3\) O.N of P + O.N of oxygen + (O.N of CI) x 3 = 0 P + —2 + —1 x 3 = 0 —P — 2 — 3 = 0 P = — 5 (ii) I. NaNO\(_3\) is neutral because it is a salt of a strong acid and a strong base, its ions do not undergo hydrolysis. II. NH\(_4\)CI is acidic because it is a salt of a strong acid and a weak base. The NH\(^+_4\) undergoes hydrolysis. III. Na\(_{4}\)CO\(_3\) is basic because it is a salt of weak acid and ntrong base. The CO\(^{2-}_3\) undergoes hydrolysis.
(c)(i) Hydrogen chloride gas (ii) downward delivery or upward displacement of air. (iii) The gas is denser than air (iv) drying the gas. (v) Physical properties — denser than air — very soluble in water — colourless gas — fumes in moist air Chemical Properties — gives cloud or white fumes in contact with ammonia vapour (vi) Pass the gas into AgNO\(_{3(aq)}\) a white precipitate of AgCl is formed wihich is soluble in aqueous ammonia but insoluble in HNO\(_3\)
(d) Mass of water = 4.30 — 2.12 = 2.18g Mass of Na\(_2\)SO\(_4\) = 23 x 2 + 32 + 16 x 4 = 142 Molar mass of H\(_2\)O = 2 + 16 = 18 2.12g of anhydrous salt contain 2.18g of water 142g of anhydrous salt contain \(\frac{2.18 \times 142}{ 2.12}\) = 146.018 X(H\(_2\)O) = 146 18x = 146 x = \(\frac{146}{18}\) = 8
