VJC_H2_CHEM_P2 Prelim

 VJC 2011 9647/02/PRELIM/11 [Turn over   2 Answer all the questions in the space provided. 1 Planning An acid can be represented by the general formula, H xA, where x represents the basicity of the acid. A bottle of a dilute aqueous solution of an acid, either monobasic or dibasic, was found. However, the label on the bottle had been damaged. Only the concentration of the acid, 1.00 mol dm3 was readable. A student was given a 1.00 mol dm 3 sodium hydroxide solution. She was asked to determine the basicity of the acid in the bottle by mixing different volumes of the acid and sodium hydroxide. (a) (i) Write an equation to repr esent the enthalpy change of neutralization between sodium hydroxide and HxA. ……………………………………………………………………………………. (ii) A student determined the basicity of the acid by performing the following experiments: Experiment 1: 30 cm 3 of HxA(aq) was added to 60 cm3 of NaOH(aq) Experiment 2: 60 cm 3 of HxA(aq) was added to 30 cm3 of NaOH(aq) The changes in temperature of the mixture were measured for Experiment 1 and Experiment 2 as T1 and T2 respectively. Suggest and explain the basicity of H xA if T1 = 2 x T2. [ 3 ]

 VJC 2011 9647/02/PRELIM/11 [Turn over   3 (b) For this part, you may assume that the acid is a monobasic acid, HA. A student decided to determine whether the acid, HA, is a strong or weak acid by performing a series of experimen ts involving mixing of hydrochloric acid with sodium hydroxide and HA with sodium hydroxide. Explain how, from the suggested exper iment, the student might be able to determine whether HA is a strong or weak acid. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ……………………………………………………………………………………... [2] FA 1 is a solution of sodium hydroxide of unknown concentration. FA 2 is 1.0 mol dm 3 of hydrochloric acid. Since neutralization reaction is exothe rmic, a series of experiments can be performed by mixing different volumes of FA 1 and FA 2 to determine the concentration of sodium hydroxide. (c) (i) Write a procedure to determine the temperature changes for the series of reactions between FA 1 and FA 2. Your answers should include choice of apparatus to measure the volume and temperature of the solutions. Give suitable headings for the columns numbered 1 to 5 as part of the plan of the experiment. Headings for 1: ………………………………………………………………………………. 2: ………………………………………………………………………………. 3: ………………………………………………………………………………. 4: ………………………………………………………………………………. 5: ………………………………………………………………………………. Volume of FA 1 /cm 3 Volume of FA 2 /cm3 1 2 3 4 5 30.00 40.00 33.00 37.00 36.