DHS_H2_CHEM_P2 ANS

2 BLANK P AGE [Turn Over

3 1(a) The chlorides of sodium to phosphorus (NaC l, MgC l2, AlCl3, SiCl 4 and PCl 5) are separately added to water. (i) Sketch a graph to show the pH of the resulting mixture, indicating the pH of sodium chloride. [2] (ii) Account for the pH value of aluminium chloride. The pH is 3. Aluminium chloride undergoes hydrolysis to give an acidic solution due to the high polarising power of Al 3+. [1] (iii) Write equations for the reactions of silicon chloride and phosphorus pentachloride with water. Silicon chloride: SiCl4 (l) + 2H2O (l)  SiO2 (s) + 4HCl (aq) Phosphorus pentachloride: PCl5 (l) + 4H2O (l)  H3PO4 (aq) + 5HCl (aq) [2] pH of chloride Na Mg Al Si P [Turn Over

4 (b) Under suitable conditions iodine and ch lorine react to give int erhalogen compound, IClx. When a pure sample of IClx was dissolved in an excess of aqueous potassium iodide, the iodine liberated requires 17.1 cm3 of 0.1 mol dm–3 of Na2S2O3 for the titration. On the other hand, the chloride ion liberated requires 12.8 cm3 of 0.1 mol dm–3 silver nitrate for complete precipitation. (i) Determine the value of x. Hence, write a balanced equation for the reaction between IClx and I–. IClx + I-  I2 + xCl- I2 + 2S2O3 2-  S4O6 2- + 2I- No. of mol of iodine = 0.0171 x 0. 1 x ½ = 8.55 x 10-4 No. of mol of Cl- = 0.0128 x 0.1 = 1.28 x 10-3 I2 : Cl- 2:3 x = 3 ICl3 + 3I-  2I2 + 3Cl- [4] (ii) Sketch on the same axes, the variation of pV m / RT against p at 300K, for 1 mol of (i) an ideal gas and (ii) IClx gas. Label your graphs clearly where V m is the gas molar volume. [2] pVm / RT p [Turn Over

5 (iii) Using the same axes as in (b)(ii), show the change at 700K for one mol of IClx. Explain your sketch. At a higher temperature, the average K.E of ICl x increases and the intermolecular forces of attractions between the molecules become less significant. [2] [Total: 13] 2 This question is about a Group II element, barium and the reactions of its compounds. (a) Write a balanced chemical equation, with state symbols, for the decomposition of barium nitrate. Ba(NO 3)2  BaO(s) + 2NO2(g) + ½ O2(g) [1] (b) How would you expect the decomposition temperature of barium nitrate to differ from that of calcium nitrate