2024 Prelims DHS H2 Chem P3 (Ans)

© DHS 2024 9729/03 [Turn over Suggested Solutions DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 CHEMISTRY Paper 3 Free Response Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/03 18 September 2024 2 hours READ THESE INSTRUCTIONS FIRST Write your centre number, index number, name and class at the top of this page. 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. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. Section A Answer all questions. Section B Answer one question. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 20 2 20 3 20 Section B 4 / 5 20 Total 80 This document consists of 22 printed pages.

2 © DHS 2024 9729/03 Section A Answer all the questions in this section. 1 (a) A bomb calorimeter and a Styrofoam cup calorimeter are both tools used in thermodynamics to measure heat changes during a chemical reaction. However, they differ significantly in their design, operation, and the type of reactions they measure. Fig. 1.1 shows a simplified diagram of a bomb calorimeter which can be used for the accurate determination of heat changes during the combustion of alkanes. Fig. 1.1 The combustion process takes place at constant volume and the reaction is initiated via the electrical heating device which ignites the mixture. (i) State one reason why the conditions inside the bomb calorimeter are considered non-standard. [1] The pressure is high inside the bomb calorimeter and hence, is different from standard conditions, which is defined as 1 atm. (ii) Suggest a reason why the Styrofoam cup calorimeter would be unsuitable to be used to measure heat changes during the combustion of alkanes. [1] Styrofoam cup calorimeter would be unsuitable in this case because the combustion reaction involve gases and they would escape from the cup.

3 © DHS 2024 9729/03 [Turn over (b) The heat capacity of a bomb calorimeter, Ccal, is the amount of heat required to raise the temperature of the calorimeter by 1 C, and it can be calculated using a fuel which the heat change is known. In an experiment to calculate Ccal, 2.00 g of liquid hexane is ignited with oxygen gas which is required to be in 20% excess. A temperature change of 12.6 °C is recorded. Under the conditions of the experiment, 1.00