EJC Prelim H2 Chemistry Paper 2 QP

© EJC [Turn Over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examination 2025 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CIVICS GROUP 2 4 – INDEX NUMBER CHEMISTRY Paper 2 Structured Questions 9729/02 02 September 2025 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, civics group, index number in the spaces 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. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Paper 2 1 / 13 2 / 16 3 / 14 4 / 14 5 / 18 Total / 75 This document consists of 22 printed pages and 2 blank pages.

2 © EJC 9729/02/J2Prelim/25 1 Mount Ijen in East Java is famous for its rare blue flames, visible at night. The phenomenon occurs when sulfur vapour , from the volcano’s cracks burns, producing bright blue flames and sulfur dioxide. In the cool high -altitude air, some of the vapour condenses into solid sulfur. (a) A team of environmental chemists were authorised to collect solid sulfur deposits near Mount Ijen’s crater to investigate volcanic activity. The chemists burnt the sulfur sample and measured the temperature change for a fixed amount of water placed in a calorimeter. The data from their experiment is shown in Table 1.1. Table 1.1 mass of solid sulfur powder burnt /g 0.76 mass of water in beaker /g 150 initial temperature of water /oC 29.8 final temperature of water / oC 39.7 (i) Construct an equation to represent the standard enthalpy change of combustion of solid sulfur, S. ................................ ................................ ................................ ...................... [1] (ii) Calculate the enthalpy change of combustion of solid sulfur , S, based on their experiment. [2]

3 © EJC 9729/02/J2Prelim/25 [Turn Over (iii) During volcanic activity, many sulfur-containing gases such as hydrogen sulfide, H2S, and sulfur dioxide, SO2, are released. In the atmosphere, H2S can oxidise to form SO2, and subsequently sulfur trioxide, SO3, may be formed. H2S(g) + 3/2 O2(g) → SO2(g) + H2O(l) ∆Hr = –562 kJ mol–1 Use the data given in Table 1.2 to calculate the enthalpy change of combustion of solid sulfur, S. Table 1.2 compound ∆Hf / kJ mol–1 H2S(g) –20.6 H2O(l) –285.8 [2] (iv) Comment on the difference in values for the enthalpy change of combustion of solid sulfur determined in (a)(ii) and (a)(iii). ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... ................................ ................................ ................................ ...................... [1] (v) With reference to a relevant chemical equation, explain how the release of sulfur-containing gases during volcanic activity can have a negative impact on the environment. ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... ................................ ................................ ................................ ...................... [2]

4 © EJC 9729/02/J2Prelim/25 (b) Sulfur in volcanic emissions primarily exists as a mixture of two stable isotopes: 32S and 34S. The chemists analysed volcanic gas samples to determine the isotopes’ relative abundance, which reveals the sulfur’s origin. • If the sample was enriched in 32S, it originated from deep mantle degassing. • If the sample was enriched in 34S, it originated from hydrothermally recycled sources. (i) 1.994 g of SO 2 evolved at Mount Ijen allowed the chemists to extract 1.00 g of elemental sulfur containing mixture of isotopes, 32S and 34S, for further analysis. Calculate the percentage by mass of 32S in the elemental sulfur extracted. You may use the chemical formula S to represent elemental sulfur in your calculations. [3] (ii) Hence, suggest the likely origin of the sulfur sample. ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... ................................ ................................ ................................ ...................... [1]

5 © EJC 9729/02/J2Prelim/25 [Turn Over While volcanic emissions affect the isotopic fractions of sulfur , the natural isotopic abundance of sulfur in Earth's environment is generally found to be present as follows. Table 1.3 isotope relative isotopic mass percentage abundance / % 32S 31.972 95.02 33S 32.971 0.75 34S 33.968 4.21 36S 35.967 0.02 (iii) Use the data in Table 1.3 to calculate the relative atomic mass of sulfur, giving your answer to two decimal places. [1] [Total: 13]

6 © EJC 9729/02/J2Prelim/25 2 Group 17 elements form a range of oxoacids with different oxidation states , such as HClO4. (a) (i) HClO4 has two central atoms; one chlorine atom and one oxygen atom. In addition, the H atom is bonded to a O atom. Draw the dot-and-cross diagram of HClO4. [1] (ii) Use VSEPR to describe and explain the shape and bond angle about central Cl and O atom in HClO4. ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... ................................ ................................ ................................ ....................... [3] (b) With reference to your answer in (a)(i), explain why HFO4 does not exist? ................................ ................................ ................................ ................................ .. ................................ ................................ ................................ .............................. [1]

7 © EJC 9729/02/J2Prelim/25 [Turn Over (c) The Latimer diagram of some chlorine species in acidic solution is given in Fig. 2.1. Fig 2.1 In Latimer diagram, oxidation numbers decrease from left to right and the numerical values of EꝊ of two adjacent species in volts. For example, the dia