2022 NYGH Chem Prelims P2

Class Centre/Index Number Name Preliminary Examination 2022 Secondary 4 CHEMISTRY Paper 2 6092/02 1 hour 45 minutes Friday 26 August 0845 – 1030 No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your name, register number and class in the spaces at the top of this page. Write in dark blue or black pen. You may use a pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid / tape. Section A (50 marks) Answer all questions in the spaces provided. Section B (30 marks) Answer all three questions, the last question is in the form either/or. Indicate in the box to the right your choice of the either/or question. 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 23. The use of an approved scientific calculator is expected, where appropriate. Examiner’s Use Paper 1 Paper 2 Indicate the question attempted for B9 with a tick (). Either  Or  Total This document consists of 23 printed pages and 1 blank page. Setter: FKD NANYANG GIRLS' HIGH SCHOOL [Turn over

2 Section A Answer all questions. Write your answers in the spaces provided on the question paper. A1 Choose from the following substances to answer the questions below. Each of these substances can be used once, more than once or not at all. Al2O3 Ar CaO CH4 CO2 Ba(NO3)2 TiO2 Pb(NO3)2 (a) Which substance forms approximately 1 % of clean, dry air? [1] (b) Which substance is the main constituent of natural gas? [1] (c) Which substance dissolves in water to form an aqueous solution which gives a white precipitate on addition of aqueous sodium chloride? [1] (d) Which substance reacts with both acids and alkalis? [1] (e) Which substance is most likely to be coloured and can be used as a catalyst? [1] (f) Which two substances are the products of thermal decomposition of limestone? [1] [Total: 6]

3 [Turn over A2 A student sets up a tube as shown in the diagram. Concentrated hydrobromic acid produces fumes of hydrogen bromide. Concentrated aqueous ammonia produces fumes of ammonia. After sometime, solid ammonium bromide appeared on the walls of the tubes. (a) (i) Calculate the relative molecular mass of hydrogen bromide and ammonia. [1] (ii) Hence, state the position ( A, B or C) of where the solid ammonium bromide may appear in the tube above. [1] (iii) Explain your answer to (a)(ii). [2] (b) Draw a ‘dot-and-cross’ diagram for ammonia. Show only the outer electrons. [2] A B C

4 (c) Explain why ammonium bromide exists as a solid at room temperature and pressure. [3] [Total: 9]

5 [Turn over A3 The analysis of compound Y shows that it has the following composition. element percentage by mass (%) nitrogen 11.1 hydrogen 3.2 chromium 41.3 oxygen 44.4 (a) Show that Y has the empirical formula N2H8Cr2O7. [3] (b) An aqueous solution of Y is orange. Deduce, with a simple reason, which element in Y is responsible for the orange colour. [1] (c) An acidified aqueous solution of Y reacts with aqueous potassium iodide to form aqueous iodine. (i) Write an ionic half-equation to show the formation of iodine from iodide ion. [1] (ii) Using your answer in (i), state and explain what you can conclude about the chemical nature of Y. [2]

6 (d) When aqueous sodium hydroxide is added to solid Y and warmed, ammonia gas is evolved. Suggest the cation present in Y that gave the above observation. [1] (e) Solid Y is a compound with the molecular formula, N2H8Cr2O7. When solid Y is heated strongly, it decomposes to only chromium(III) oxide, water and nitrogen gas. Write a balanced chemical equation to show this decomposition. State symbols are not required. [2] [Total: 10]

7 [Turn over A4 Iron(II) sulfide is a compound that can be made by heating iron filings with sulfur powder. (a) For each of the statements below, put a tick () in one box in each row that corresponds with a mixture of iron and sulfur or a compound of iron and sulfur. statement mixture compound (i) Chemical properties are the same as those of its components. (ii) During its formation, energy change is involved. (iii) Has fixed composition. (iv) Components can be separated by magnetism. [2] (b) The enthalpy change of the reaction between iron and sulfur to form iron(II) sulfide is -100 kJ/mol. Complete the energy profile diagram for this reaction. You should include  the formula of the product,  a label for the activation energy,  a label for the enthalpy change of reaction. [3] (c) Iron(II) sulfide reacts with hydrochloric acid to form hydrogen sulfide. An aqueous solution of hydrogen sulfide behaves as a weak acid. Explain what is meant by the term weak acid. [1] energy progress of reaction Fe(s) + S(s)

8 (d) Iron(II) sulfate can be prepared by reacting iron with dilute sulfuric acid. Fe(s) + H2SO4(aq) → FeSO4(aq) + H2(g) (i) Write an ionic equation for this reaction. [2] (ii) A student claimed that she could obtain pure, dry iron(II) sulfate by adding an equal volume of aqueous sodium hydroxide into iron(II) sulfate solution before filtering to obtain its residue. State the observation upon addition of aqueous sodium hydroxide and explain why the student is incorrect. [2] (iii) Describe how you would obtain crystals of pure, dry iron( II) sulfate from iron(II) sulfate solution. [2] [Total: 12]

9 [Turn over A5 The table below shows some information about the extraction of metals from molten electrolytes using electrolysis. metal extracted electrolyte amount of electrons needed to extract 10 g of the metal/ mol sodium molten sodium chloride 0.435 calcium molten calcium chloride magnesium molten magnesium chloride 0.833 (a) In the space below, construct a simple diagram to represent the set up for an electrolytic cell using molten sodium chloride as the electrolyte. Include on the diagram suitable electrodes that can be used for this cell, as well as the direction of electron flow. [2]

10 (b) (i) State the electrode where calcium metal is formed at. [1] (ii) With the help of a suitable ionic half -equation, calculate the amount of electrons needed to form 10 g of calcium metal. amount of electrons = [2] (c) A student suggested using aqueous magnesium chloride as an electrolyte to extract magnesium metal. With reference to the ions present, explain why the student would not be able to obtain any magnesium metal. [2] [Total: 7]