Copy of MGS Chemistry P2

Page 2 of 28 Methodist Girls’ School Chemistry Paper 2 Sec 4 Preliminary Examination 2024 Section A (70 marks) Answer all the questions. 1 (a) Some chemical equations, A to F, are shown. A Ba 2+ (aq) + SO42- (aq) → BaSO4(s) B CO32- (aq) + 2H+ (aq) → CO2 (g) + H2O (l) C Ag + (aq) + I- (aq) → AgI (s) D H + (aq) + OH- (aq) → H2O (l) E 2I- (aq) + Br2 (aq) → I2 (aq) + 2Br- (aq) F NH4+ (aq) + OH- (aq) → H2O (l) + NH3 (aq) Answer the following questions using the equations. Each equation may be used once, more than once or not at all. Give the letter, A to F, for the equation which shows: (i) the formation of a gas that turns moist red litmus paper blue [1] (ii) a reaction that forms a white precipitate [1] (iii) a displacement reaction [1] (b) Ammonium ion, NH4+, is a polyatomic ion. Ammonium ion is formed when ammonia reacts with hydrogen ion. The nitrogen atom in ammonia contributes and donates a pair of valence electrons to one hydrogen ion to form a covalent bond. Draw a ‘dot and cross’ diagram to show the covalent bonding in ammonium ion using the key provided. Show outer electrons only. [2] [Total: 5] Key: x : electron of hydrogen • : electron of nitrogen

Page 3 of 28 Methodist Girls’ School Chemistry Paper 2 Sec 4 Preliminary Examination 2024 2 Copper is a transition element. The flowchart in Fig. 2.1 shows how copper can be made from copper (II) carbonate, either in the industry, or on a small scale in the laboratory. Copper(II) carbonate, CuCO3 Copper(II) oxide, CuO Copper, water and impurities Copper, Cu Fig. 2.1 (a) (i) Identify gas X. [1] (ii) State the type of reaction that takes place when copper(II) oxide is heated with carbon. [1] (iii) Write an equation for the reaction in (a)(ii). [1] Shake solids left behind with water Heat Heat with carbon Solid copper sinks to the bottom. Pour off water and impurities to leave copper. Put wet copper in an oven to dry gas X water and impurities

Page 4 of 28 Methodist Girls’ School Chemistry Paper 2 Sec 4 Preliminary Examination 2024 (b) Jane uses the procedure in the flowchart to make copper in the laboratory. She uses the following graph shown in Fig. 2.2 to predict the theoretical yield of copper. (i) Explain why the line on the graph in Fig. 2.2 starts at 0 on both axes. [1] (ii) Jane wants to make a theoretical yield of 40.0 g of copper. Using the graph in Fig. 2.2 , predict the starting mass of copper(II) carbonate she should use. Explain your answer. [2] mass of copper(II) carbonate at the start /g theoretical yield of copper /g 0 10 20 40 60 20 30 Fig. 2.2

Page 5 of 28 Methodist Girls’ School Chemistry Paper 2 Sec 4 Preliminary Examination 2024 (iii) Jane conducts the experiment. The mass of copper that she obtained is higher than the maximum yield of 40.0 g. Which two mistakes could lead to an incorrectly high yield? Tick (✓) two boxes. She did not use enough copper carbonate. She did not dry the copper at the end. She did not heat the copper oxide for long enough. She used copper that contains solid impurities. [2]

Page 6 of 28 Methodist Girls’ School Chemistry Paper 2 Sec 4 Preliminary Examination 2024 (c) Nina and Kai also follow the flowchart to make some copper. They compare the mass of copper they make at the end with each other as shown in Table 2.1. Table 2.1 They make statements about their results. Student Mass of copper(II) carbonate at the start / g Theoretical yield of copper / g Mass of copper made / g Nina 50.0 26.0 18.0 Kai 10.0 5.0 4.8 Using the data in Table 2.1, explain why Kai is correct with the help of chemical calculations. [2] [Total: 10] Nina I have made much more copper than you. Kai Yes, but I have extracted more copper from the 10 g of CuCO3 than you from the 50 g of CuCO3.

Page 7 of 28 Methodist Girls’ School Chemistry Paper 2 Sec 4 Preliminary Examination 2024 3 Magnesium is one of the most abundant elements on Earth. It is used extensively in the production of magnesium-aluminum alloys. It is produced by the electrolysis of molten magnesium chloride. A schematic diagram of the electrolytic cell is shown in Fig 3.1. Fig. 3.1 (a) Write a balanced half-equation for the reactions occurring at the Cathode: [1] Anode: [1] (b) Explain why an inert gas is constantly blown through the surface of the molten magnesium. [1] (c) Explain why it is necessary to lower the melting point of magnesium chloride by adding sodium chloride and calcium chloride. [1] graphite anode inert gas in molten magnesium chlorine gas molten magnesium chloride (with some NaCl and CaCl2) chlorine gas iron cathode molten magnesium inert gas out

Page 8 of 28 Methodist Girls’ School Chemistry Paper 2 Sec 4 Preliminary Examination 2024 (d) The graphite anode is now replaced with an iron rod. With the help of a half-equation, explain the difference in the observation at the anode. [2] [Total: 6]

Page 9 of 28 Methodist Girls’ School Chemistry Paper 2 Sec 4 Preliminary Examination 2024 4 Propanone, CH3COCH3, reacts with iodine, I2, to form colourless products. The reaction is catalysed by hydrochloric acid. Table 4.1 shows how the relative rate of this reaction changes when different concentrations of propanone, iodine and hydrochloric acid are used. Table 4.1 experiment concentration of CH3COCH3 in mol/dm3 concentration of I2 in mol/dm3 concentration of HCl in mol/dm3 relative rate of reaction 1 0.025 0.024 0.12 5.1 2 0.050 0.024 0.12 10.2 3 0.050 0.024 0.06 5.1 4 0.050 0.012 0.06 5.1 (a) Use the information in Table 4.1 to describe how increasing the concentration of each of these substances affects the relative rate of reaction. Propanone: Iodine: [2] (b) Increasing the temperature increases the rate of this reaction. Use ideas about energy and collisions to explain the effect of temperature on the rate of reaction. [2]

Page 10 of 28 Methodist Girls’ School Chemistry Paper 2 Sec 4 Preliminary Examination 2024 (c) Sketch two graphs in Fig. 4.1 to show the effect of concentration of hydrochloric acid on the rate of reaction between propanone and iodine. Label your graphs with the chosen experiments. Fig. 4.1 [1] (d) Iodine has many isotopes. I odine−127 and Iodine−130 are two common isotopes of iodine. Complete Table 4.2 to show the number of particles in these two isotopes of iodine. Table 4.2 [2] isotope number of electrons number of neutrons Iodine−127 Iodine−130 [Total: 7] Mass of colourless product formed / g Time/s

Page 11 of 28 Methodist Girls’ School Chemistry Paper 2 Sec 4 Preliminary Examination 2024 5 Methylamine, CH3NH2, is a weak base. Its properties are similar to those of ammonia. (a) When methylamine is dissolved in water, the following equilibrium is set up. CH3NH3+ + OH- CH3NH2 + H2O (i) Suggest wh