2022 CCHS(M) Chem Prelims P2

[Turn over Name: Class: Class Register Number: Parent’s Signature ______________________ PRELIMINARY EXAMINATION 2022 SECONDARY 4 CHEMISTRY 6092/02 Paper 2 12 September 2022 1 hour 45 minutes Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your name, class and register number clearly in the spaces provided 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. Section A Answer all questions in the spaces provided. Section B Answer all three questions, the last question is in the form either/or. Answer all questions in the spaces provided. The number of marks is given in brackets [ ] at the end of each question or part question. A copy of the Periodic Table is printed on page 24. The use of an approved scientific calculator is expected, where appropriate. For Examiner’s Use Section A / 50 Section B B6 / 12 B7 / 8 B8 ( ) / 10 Total / 80 This document consists of 24 printed pages.

2 2022 Preliminary Exam/CCHMS/Secondary 4 /Chemistry/6092/02 Section A Answer all questions in this section in the spaces provided. The total mark for this section is 50. A1 The formulae of some gases are given in the following list. NH3 O2 CO Cl2 He CO2 SO2 NO H2 CH4 Choose formulae from above to answer the following questions. You may use each formula once, more than once or not at all. (a) Give the formulae of two gases which are elements. .................……………………………………………………………………………………….. [1] (b) Give the formulae of two gases that will change the colour of a damp red litmus paper. .................……………………………… and …………… …... ……………………………….. [1] (c) Give the formulae of two gases that are involved in both respiration and photosynthesis. .................……………………………… and …………… …... ……………………………….. [1] (d) Give the formula of a gas that contains an element with an oxidation state of –4. .................……………………………………………………………………………………….. [1] (e) Give the formula of a gas which is oxidised in the catalytic convertor. .................……………………………………………………………………………………….. [1] [Total: 5]

3 2022 Preliminary Exam/CCHMS/Secondary 4 /Chemistry/6092/02 [Turn over A2 The table shows some information about the atoms of elements A, B, C, D, E and F. (The letters do not represent the atomic symbols of the elements.) element number of protons number of neutrons nucleon number A 8 6 14 B 7 7 14 C 37 85 D 19 20 39 E 8 9 17 F 26 30 (a) (i) Fill in the blanks in the table above. [1] (ii) Write the electronic configuration of element D. .......……………………………………………………………………………………… ..[1] (iii) E can form a stable ion. Write the formula of this ion. .......……………………………………………………………………………………… ..[1] (iv) Identify the isotopes of the same element from the table. Explain your answer. ......……………………………………………………………………………………… …... .......……………………………………………………………………………………… ..[1] (b) (i) Use the information in the table to identify the elements B, D and F. B: ………………………… D: ………………………… F: ………………………… [1] (ii) State the trend in the melting point of the elements B, D and F. Highest melting point ………………………. ……………………… Lowest melting point ……………………… [1]

4 2022 Preliminary Exam/CCHMS/Secondary 4 /Chemistry/6092/02 (iii) Explain your reasoning for the difference in melting points for B and F. .......……………………………………………………………………………………… …... .......……………………………………………………………………………………… …... .......……………………………………………………………………………………… …... .......……………………………………………………………………………………… ...[2] (c) B and C can react to form a compound. Draw a dot-and-cross diagram to show the bonding in this compound. Show outer shell electrons only. [2] [Total: 10]

5 2022 Preliminary Exam/CCHMS/Secondary 4 /Chemistry/6092/02 [Turn over A3 The Winkler Method can be used to determine the oxygen concentration in water samples. The reactions involved are: Step 1: Manganese(II) sulfate is added to an excess of alkali. MnSO4 (aq) + 2KOH (aq) → Mn(OH)2 (s) + K2SO4 (aq) Step 2: The resulting mixture above is added to 100 cm3 of water containing dissolved oxygen. 2H2O (l) + 4Mn(OH)2 (s) + O2 (aq) → 4Mn(OH)3 (s) Step 3: An excess of acidified potassium iodide is then added. 2Mn(OH)3(s) + 2KI(aq) + 3H2SO4(aq) → 2MnSO4(aq) + K2SO4(aq) + I2(aq) + 6H2O(l) Step 4: The mixture is then transferred to a conical flask and titrated with a standard solution of sodium thiosulfate using starch as an indicator. I2 (aq) + 2Na2S2O3 (aq) → 2NaI (aq) + Na2S4O6 (aq) colourless colourless (a) State two observations where manganese shows the typical characteristics of a transition element during these reactions. .................……………………………………………………………………………………… ….. .................……………………………………………………………………………………… ….. .....................…………………………………………………………………………………… .[2] (b) Write the ionic equation for step 3. .................……………………………………………………………………………………… ..[1] (c) Sulfur can exhibit two oxidation states. Table 3.1 oxidation state of sulfur Na2S2O3 Na2S4O6 +2.5 (i) Fill in the missing oxidation state of sulfur in Table 3.1. [1] (ii) Use oxidation states to show why step 4 is a redox reaction. .................………………………………………………………………………………… …. .................………………………………………………………………………………… …. .................………………………………………………………………………………… [2]

6 2022 Preliminary Exam/CCHMS/Secondary 4 /Chemistry/6092/02 (d) State the colour change of the end point in step 4. .................……………………………………………………………………………………… .[1] (e) A 100 cm3 sample of water containing dissolved oxygen required 11.20 cm3 of 0.0100 mol/dm3 sodium thiosulfate solution to reach the end point. Calculate the concentration of oxygen in this sample of water in mol/dm3. [3] [Total: 10]

7 2022 Preliminary Exam/CCHMS/Secondary 4 /Chemistry/6092/02 [Turn over A4 Methane, methanol and hydrogen have been investigated as possible alternative fuels for motor vehicles that currently use petrol. The table below compares the energy released on combustion of these fuels. The enthalpy change of combustion of a substance, ΔHc, is defined as the energy released when one mole of the substance is completely burnt in oxygen. fuel density / g/dm3 ΔHc / kJ/mol energy per gram / kJ/g petrol 710 – 770 – 47.3 methane to be calculated –891 55.7 methanol 792 –726 to be calculated hydrogen 0.0884 –286 143 (a) (i) Calculate the density for methane in g/dm3. .......……………………………………………………………………………………… ..[1] (ii) Calculate the energy per gram for methanol in kJ/g. .......……………………………………………………………………………………… ..[1] (iii) Suggest why no value is quoted for the enthalpy change of combustion of petrol in the table above. …………………………………………………………………………………………… …... ..