2024 NYJC H1 Chem 8873 P2

[Turn over NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 1 CANDIDATE NAME CLASS TUTOR’S NAME CHEMISTRY 8873/02 Paper 2 Structured Questions 9 September 2024 2 hours Candidates answer on the Question Paper Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class in the spaces provided at the top of this page. Write in dark blue or black pen. You may use a soft pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all questions. Section B Answer one question. 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 1 /9 2 /8 3 /9 4 /10 5 /15 6 /9 7/8 /20 Total /80 This document consists of 26 printed pages. H

2 H1 Chemistry 8873/02 NYJC J2/24 PX [Turn Over For Examiner's Use Section A Answer all questions in the spaces provided. 1 This question is about the chemistry of sodium and oxygen. (a) (i) Define the term first ionisation energy. ......................................................................................................................... ......................................................................................................................... ..................................................................................................................... [1] (ii) Explain the following comparisons of ionisation energies. • The first ionisation energy of Na (494 kJ mol –1) is very much lower than that of oxygen (1310 kJ mol–1). ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ..................................................................................................................... [2] • The second ionisation energy of Na (4 560 kJ mol –1) is very much higher than its first ionisation energy (494 kJ mol–1). ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ..................................................................................................................... [1]

3 H1 Chemistry 8873/02 NYJC J2/24 PX [Turn Over For Examiner's Use (b) When sodium is burned in oxygen, both sodium oxide Na 2O and sodium peroxide Na2O2 are produced. The two products are strongly basic and form sodium hydroxide when reacted with water. Hydrogen peroxide is also formed in the reaction of sodium peroxide with water. (i) Explain, in terms of electronegativity, why Na2O and Na2O2 are strongly basic. ......................................................................................................................... ..................................................................................................................... [1] (ii) Draw a dot -and-cross diagram and label the two different types of bonding present in sodium peroxide, Na2O2. [2] (iii) Explain why the melting point of Na2O (1132 oC) is very much higher than that of Na2O2 (460 oC). ........................................................................................................................ ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ..................................................................................................................... [2] [Total: 9]

4 H1 Chemistry 8873/02 NYJC J2/24 PX [Turn Over For Examiner's Use 2 For many compounds the enthalpy change of formation cannot be calculated directly. An indirect method based on enthalpy changes of combustion can be used. The enthalpy change of combustion can be found by a calorimetry experiment in which the heat energy given off during combustion is used to heat a known mass of water and the temperature change recorded. (a) (i) Define the term standard enthalpy change of combustion. ......................................................................................................................... ......................................................................................................................... ..................................................................................................................... [1] (ii) Write the equation for the standard enthalpy change of combustion of ethanol, C2H5OH. ..................................................................................................................... [1] (b) In an experiment to determine the enthalpy change of combustion of ethanol, 0.288 g of ethanol was burn ed and the heat given off raised the temperature of 100 g of water by 16.3 oC. (i) Calculate the standard enthalpy change of combustion of ethanol. Assume that the process is only 80% efficient, the specific heat capacity of water is 4.2 J g−1 K−1. [3] (ii) Other than heat loss to surroundings, suggest a reason why the value for the standard enthalpy change of combustion of ethanol determined by a simple laboratory calorimetry experiment is likely to be lower than the true value. ......................................................................................................................... ......................................................................................................................... ..................................................................................................................... [1]

5 H1 Chemistry 8873/02 NYJC J2/24 PX [Turn Over For Examiner's Use (c) Some relevant standard enthalpy change of combustion values, Hc, are given in Table 2.1. Table 2.1 substance Hc / kJ mol–1 C(s) –393.5 H2(g) –285.8 C3H7OH(l) –2021.0 Using the data in Table 2.1, calculate the standard enthalpy change of formation of C3H7OH(l), Hf. Hf 3C(s) + 4H2(g) + ½O2(g) → C3H7OH(l) [2] [Total: 8]

6 H1 Chemistry 8873/02 NYJC J2/24 PX [Turn Over For Examiner's Use 3 When ethanoic acid reacts with ethanol to form ethyl ethanoate and water, the fo