MI Prelim P4 Ans

Class Adm No Candidate Name: This question paper consists of 18 printed pages and 0 blank pages. 2018 Preliminary Exams Pre-University 3 H2 CHEMISTRY 9729/04 Paper 4 Practical 10th Sept 2018 2 hour 30 mins Candidates answer on the Question paper. READ THESE INSTRUCTIONS FIRST Do not turn over this question paper until you are told to do so Write your name, class and admission number on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. Qualitative Analysis Notes are printed at the back of the Question Paper. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. Question 1 2 3 4 Total Marks 26 13 6 10 55 Shift Laboratory

2 1 Investigation of acid-base titrations involving sodium hydrogen carbonate According to the Arrhenius theory of acids and bases, an acid produces H +(aq) ions and a base produces OH–(aq) ions. The reaction of these two ions to form water molecules is known as acid- base neutralisation. The equation for this neutralisation reaction is given below, and strong acid–strong base reactions are known to have an enthalpy change of neutralisation (∆Hneu) of approximately –57.1 kJ mol-1. H+(aq) + OH–(aq) → H2O(l) ∆Hneu = –57.1 kJ mol-1 However, the ∆Hneu for weak acid–strong base reactions are known to differ. Sodium hydrogen carbonate, NaHCO3, is an example of a weak acid. FA 1 is 1.8 mol dm-3 sodium hydrogen carbonate, NaHCO3. FA 2 is sodium hydroxide, NaOH, of concentration between 0.9 – 1.2 mol dm-3. NaHCO3 + NaOH → Na2CO3 + H2O ∆Hneu’ As the precise concentration of FA 2 is unknown, determination of ∆Hneu’ can be done using a thermometric titration to simultaneously determine both the concentration of FA 2 as well as ∆Hneu’. Thermometric titration is a technique whereby equivalence points of a reaction can be located by observing temperature changes, hence eliminating the need for an indicator. In 1(a), you will perform a weak acid–strong base thermometric titration. The data from this titration will be used to determine: • the titration value at equivalence point, Veq, • the precise concentration of FA 2, [NaOH], • the maximum temperature change, ∆Tmax, • the enthalpy change of neutralisation, ∆Hneu’. For Examiners’ Use

3 [Turn over (a) Determination of Veq and ∆Hneu’ using thermometric titration For this experiment, you will need