2019 TMJC H2 Chem Prelim P4 ANS

1 1 Determination of the concentration of a base and the enthalpy change of the neutralisation reaction FA 1 is 2.0 mol dm–3 sulfuric acid, H2SO4. FA 2 is aqueous sodium hydroxide, NaOH. The reaction of sulfuric acid and sodium hydroxide is exothermic. In separate experiments, you will add increasing volumes of FA 2 to a fixed volume of FA 1. In each experiment you will measure the maximum temperature rise, ∆T. As the volume of FA 2 is increased, this maximum temperature rise, ∆T, will increase and then decrease. By measuring the maximum temperature rise for differe nt mixtures of the two reagents, you are to determine the following:  the concentration of sodium hydroxide, NaOH, in FA 2  the enthalpy change when 1 mol of H2SO4 is neutralised by NaOH (a) Method  Fill the labelled burette with FA 1.  Support a styrofoam cup in the 250 cm3 beaker.  Run 10.00 cm3 of FA 1 from the burette into the styrofoam cup.  Measure 20.0 cm3 of FA 2 using a measuring cylinder.  Place the thermometer in the FA 2 in the measuring cylinder and record the steady temperature of the solution.  Pour the FA 2 into the styrofoam cup, stir and record the maximum temperature obtained in the reaction.  Empty and rinse the styrofoam cup; shake dry the styrofoam cup. Rinse the thermometer.  Carry out the experiment three more times. Each time use 10.00 cm3 of FA 1.  Use 30.0 cm3, 40.0 cm3 and 50.0 cm3 of FA 2 in these different experiments. Carry out two further experiments. Choose volumes of FA 2 which will allow you to investigate more precisely the volume of FA 2 that produces the highest temperature rise when added to 10.00 cm3 of FA 1. TAMPINES MERIDIAN JUNIOR COLLEGE 2019 JC2 H2 Chemistry Prelim Exam Paper 4 (Suggested Answers)

2 Results Record your results below in an appropriate form showing, for each experiment, the volumes of solutions used, temperature measurements and the temperature rise, T. Expt Volume of FA 1 / cm3 Volume of FA 2 / cm3 Ti / oC Tf / oC ∆T / oC 1 10.00 20.0 31.5 42.5 11.0 2 10.00 30.0 31.5 45.0 13.5 3 10.00 40.0 31.5 44.0 12.5 4 10.00 50.0 31.5 42.0 10.5 5 10.00 25.0 31.5 43.5 12.0 6 10.00 35.0 31.5 45.0 13.5 [4] (b) Plot a graph of temperature rise, ∆T, on the y-axis against the volume of FA 2 added on the x-axis. Draw a line of best fit through the points where the temperature rise is increasing and another line through the points where the temperature rise is decreasing. The intersection of these lines represents the temperature rise for the volume of FA 2 that exactly neutralises the sulfuric acid present in 10.00 cm3 of FA 1. [3] ∆T / oC 15.0 14.0 13.0 12.0 11.0 10.0 Vol of FA 2 / cm3 10.0 20.0 30.0 40.0 50.0 X X X X X X (c) 32.5 (e) 14.0

3 (c) Read from the graph the volume of FA 2 that gives the maximum te