JPJC Prelim 2025 Paper 4 Answers_H2 Chem

© Jurong Pioneer Junior College [Turn Over NAME Suggested Answer Scheme 1 Determination of the enthalpy change for the reaction between NaOH and CO2 In this experiment you will determine the enthalpy change, H1, for the reaction shown in equation 1. equation 1 NaOH(aq) + CO2(g) → NaHCO3(aq) H1 Sodium hydrogencarbonate and sodium hydroxide each react with sulfuric acid as shown in equations 2 and 3. equation 2 2NaHCO3(s) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l) + 2CO2(g) H2 equation 3 2NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l) H3 You will determine the values of H2 and H3 and use Hess’s law to calculate H1. (a) (i) Reaction of sodium hydrogen carbonate with sulfuric acid FA 1 is solid sodium hydrogen carbonate FA 2 is 1.0 mol dm–3 sulfuric acid, H2SO4 In this experiment, you will measure the initial temperature of sulfuric acid in a polystyrene cup. After a sample of sodium hydrogen carbonate is added to sulfuric acid which is in excess, you will measure the minimum temperature reached in the experiment. You will then determine the temperature fall caused by the reaction. In the space provided on page 3, prepare tables in which to record for the experiment: • all weighings to an appropriate level of precision, • all required temperature measurements to an appropriate level of precision. Procedure: 1. Weigh the capped bottle containing solid FA 1. 2. Using a measuring cylinder, transfer 50.0 cm 3 of FA 2 into a polystyrene cup. Place this cup inside a second polystyrene cup, which is placed in a 250 cm3 glass beaker. 3. Place the thermometer in this FA 2 and record the initial temperature, Ti. 4. Adding small quantities at a time, tip all the FA 1 into the FA 2 in the polystyrene cup. 5. Using the thermometer, stir the mixture continuously until it reaches its minimum temperature. Record this temperature, Tmin. 6. Calculate and record the temperature fall. 7. Weigh the capped bottle with any residual FA 1 and record the mass of FA 1 added.

2 © Jurong Pioneer Junior College 9729/04/J2 PRELIMINARY EXAM/2025 Results Mass of capped bottle with FA 1 /g 11.658 Mass of capped bottle with residual FA 1 / g 5.661 Mass of FA 1 added / g 5.997 Initial temperature/ Ti oC 30.5 Minimum temperature/ Tmin / oC 24.2 Temperature fall / oC 6.3 [3] (a) (ii) Calculate the heat change, q, for your experiment in 1(a)(i). You should assume that the specific heat capacity of the solution is 4.18 J g−1 K−1, and that the density of the solution is 1.00 g cm−3. q = 50.0  4.18  1.00  6.3 = 1317 J = 1.32 kJ [1] (iii) Determine the enthalpy change for the reaction of sodium hydrogen carbonate with sulfuric acid, H2. In this reaction, sulfuric acid is used in excess. 2NaHCO3(s) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l) + 2CO2(g) H2 Include the sig