2024 TMJC H1 Chem Prelim P2 (QP)

CANDIDATE NAME CIVICS GROUP ______________________________________________________________________________ H1 CHEMISTRY 8873/02 Paper 2 Structured Questions 12 September 2024 2 hours Candidates answer on the Question Paper. Additional materials: Data Booklet ______________________________________________________________________________ READ THESE INSTRUCTIONS FIRST Write your name and civics group in the spaces provided at the top of this page. Write in dark blue or black pen on both sides of the paper. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all the 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. ________________________________________________________________________________________ This document consists of 25 printed pages and 1 blank page. Examiner’s Use Paper 1 MCQ / 30 Paper 2 Section A Q1 / 9 Q2 / 6 Q3 / 14 Q4 / 8 Q5 / 10 Q6 / 13 Section B Q7 / 20 Q8 / 20 / 80 Total / 100 Grade TAMPINES MERIDIAN JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION

2 Tampines Meridian Junior College 2024 JC2 Preliminary Examination H1 Chemistry Section A Answer all the questions in this section in the spaces provided. 1 (a) Aluminium and boron are two elements of Group 13. (i) Complete the electronic configuration for Al and Al3+. Al: 1s2 ………………………………. Al3+: 1s2 ………………………………. [1] (ii) Atoms of elements are made up of the three subatomic particles: protons, electrons and neutrons, in varying numbers. Complete Table 1.1 for each subatomic particle of an atom of Al13 26 . Table 1.1 [1] (b) The compounds of aluminium and boron have many uses. Alumin ium oxide, Al2O3, is commonly used as a refractory material for lining furnaces while aluminium chloride, AlCl3, is an antiperspirant agent. Boron trichloride, BCl3, is used in the refining process of aluminium. (i) Draw the dot-and-cross diagrams for Al2O3 and AlCl3. [2] (ii) Briefly describe the bonding in AlCl3 in terms of the overlap of orbitals. ………………………………………………………………………………………………. …………………………………………………………………………………………… [1] atom number of protons number of neutrons number of unpaired electrons Al13 26

3 Tampines Meridian Junior College 2024 JC2 Preliminary Examination H1 Chemistry [Turn over (iii) With reference to the Valence Shell Electron Pair Repulsion Theory , explain the shape and bond angle with respect to the B atom in BCl3. ………………………………………………………………………………………………. ………………………………………………………………………………………………. ………………………………………………………………………………………………. …………………………………………………………………………………………… [2] (c) Table 1.2 shows the melting points of two different boron compounds, BCl3 and NaBH4. Table 1.2 compound melting point / °C BCl3 – 107 NaBH4 400 With reference to structure and bonding, explain the difference in melting points of the two compounds. ……………………………………………………………………………………………….…… ………………………………………………………………………………………….………… …………………………………………………………………………………….……………… ……………………………………………………………………………….…………………… ………………………………………………………………………………………………… [2] [Total: 9]

4 Tampines Meridian Junior College 2024 JC2 Preliminary Examination H1 Chemistry 2 This question is about ionisation energies of elements. (a) (i) Define the term first ionisation energy. ………………………………………………………………………………………………. ………………………………………………………………………………………………. …………………………………………………………………………………………… [1] (ii) Explain the general trend in first ionisation energy of elements down a Group in the Periodic Table. ………………………………………………………………………………………………. ……..……………………………………………………………………………………….. ………………………………………………………………………………………..…….. ………………..…………………………………………………………………………….. …….…………………………………………………………………………………….. [2] (b) The first six ionisation energies for an unknown element X is given in Table 2.1. Table 2.1 1st 2nd 3rd 4th 5th 6th ionisation energy of X / kJ mol–1 1050 1900 2910 4960 6270 21300 (i) Deduce the Group number of element X, giving your reasoning. ………………………………………………………………………………………………. ………………………………………………………………………………………………. ………………………………………………………………………………………………. …………………………………………………………………………………………... [2]

5 Tampines Meridian Junior College 2024 JC2 Preliminary Examination H1 Chemistry [Turn over (ii) The graph in Fig . 2.1 shows a sketch of the first ionisation energies of six consecutive elements within Periods 2 and Period 3. The letters do not represent the symbols of elements. Fig. 2.1 Identify the alphabet letter in Fig. 2.1 that belongs to element X. ………………………………………………………………………………………...… [1] [Total: 6] / kJ mol–1

6 Tampines Meridian Junior College 2024 JC2 Preliminary Examination H1 Chemistry 3 (a) Ethanoic acid is a weak acid. CH3COOH CH3COO– + H+ A sample of ethanoic acid can be mixed with aqueous sodium ethanoate to make a buffer solution. (i) Define the term pH. …………………………………………………………………………………………….… …………………………………………………………………………………………… [1] (ii) Explain with aid of equations, how the sample mixture of ethanoic acid and sodium ethanoate behaves as a buffer. ………………………………………………………………………………………………. ………………………………………………………………………………………………. ………………………………………………………………………………………………. ………………………………………………………………………………………………. ………………………………………………………………………………………………. …………………………………………………………………………………………… [3] (iii) The sample of ethanoic acid with a pH value of 3.0 has a molar concentration of 0.0750 mol dm–3. The degree of dissociation, , is the percentage of acid molecules that dissociate into ions:  = [acid]dissociated [acid]initial  100% Using this information, determine  for the sample of ethanoic acid.  = ……………………..% [2]

7 Tampines Meridian Junior College 2024 JC2 Preliminary Examination H1 Chemistry [Turn over (b) A student determines the concentration of ethanoic acid in a sample of vinegar by titrating it with aqueous sodium hydroxide. CH3COOH + NaOH → CH3COO–Na+ + H2O A 10.0 cm3 portion of the sample of vinegar is transferred into a 250 cm3 volumetric flask. The solution is made up to 250 cm3 with deionised water. Several 25.0 cm 3 portions of this diluted vinegar are titrated against 0.0 220 mol dm –3 sodium hydroxide, using thymolphthalein indicator. The mean volume of aqueous sodium hydroxide added is 21.10 cm3. (i) Calculate the concentration, in mol dm–3, of ethanoic acid in the original sample of vinegar. [2]

8 Tampines Meridian Junior College 2024 JC2 Preliminary Examination H1 Chemistry (ii) The minimum legal acidity level of vinegar in most countries is 4% by mass . Below this level, it cannot be sold as vinegar. Calculate the percentage by mass of ethanoic acid in the original sample of vinegar and state whether the vinegar meets the minimum legal acidity level. Assume the density of vinegar to be 1 g cm–3. [2] (c) Ethanoic acid can be reduced to form ethanol, C2H5OH, which is useful as fuel. A direct-ethanol fuel cell (DEFC) is a type of fuel cell that uses ethanol as a fuel source. The redox reaction in DEFC involves the oxidation of ethanol to carbon dioxide and the reduction of oxygen to water. (i) Determine the average oxidation number of carbon in ethanol and the oxidation number of carbon in carbon dioxide. [1] (ii) Construct the half-equations for the redox reaction in the DEFC. ………………………………………………………………………………………………. …………………………………………………………………………………………… [2] (iii) Hence, or otherwise, write the overall equati