11. A mixture of magnesium bromide and magnesium sulfate is known to contain 3 mol of magnesium and 4 mol of bromide ions. How many moles of sulfate ions Are present? A 1 B 2 C 3 D 4 12. 5 g of copper is added to excess silver nitrate solution. The equation for the reaction that takes place is: After some time, the solid present is filtered off from the solution, washed with water, dried and weighed. The final mass of the solid will be A less than 5 g B 5g C 10g D more than 10 g. 13. A pupil added 0·1 mol of zinc to a solution containing 0·05 mol of silver(I) nitrate. Zn(s) + 2AgNO3(aq) → Zn(NO3)2(aq) + 2Ag(s) Which of the following statements about the experiment is correct? A 0·05 mol of zinc reacts. B 0·05 mol of silver is displaced. C Silver nitrate is in excess. D All of the zinc reacts. 14. 0·5 mol of copper(II) chloride and 0·5 mol of copper(II) sulphate are dissolved together in water and made up to 500 cm3 of solution. What is the concentration of Cu2+ ions in the solution in moll-1 A 0·5 B 1·0 C 2·0 D 4·0
5. Aluminium reacts with oxygen to form aluminium 2Al(s) + 1½O2(g) → ΔH = −1670 kJ mol−1 What is the enthalpy of combustion of aluminium in kJ mol−1? A −835 B −1113 C −1670 D +1670 6. What is the relationship between a, b, c and d? A a = b + c – d B a = d – b – c C a = b – c – d D a = d + c – b 7. Given the equations then, according to Hess’s Law A c = a – b B c = a + b C c = b – a D c = – b – a. 8. What is the relationship between a, b, c and d? A a = c + d − b B a = b − c − d C a = −b − c − d D a = c + b + d
16. Different are used for different purposes. (a) Ethanol, C2H5OH, can be used as a fuel in some camping stoves. (i) The enthalpy of combustion of ethanol given in the data booklet is −1367 kJ mol−1. this value, calculate the mass of ethanol, in g, required to raise the temperature of 500 g of water from 18 °C to 100 °C. Show your working clearly. (3) (ii) Suggest two reasons why less energy is obtained from burning ethanol in the camping stove than is predicted from its enthalpy of combustion. (2) (b) Petrol is a fuel used in cars. A car has a 50·0 litre petrol tank. Calculate the energy, in kJ, released by the complete combustion of one tank of petrol. (2) 17. Hydrogen has been named as a ‘fuel for the future’. In a recent article researchers reported success in making hydrogen from glycerol: C3H8O3(l) → CO2(g) + CH4(g) + H2(g) (a) Balance this equation. (1) (b) The enthalpy of formation of glycerol is the enthalpy change for the reaction: 3C(s) + 4H2(g) + 1½O2(g) → C3H8O3(l) (graphite) Calculate the enthalpy of formation of glycerol, in kJ mol–1, information from the data booklet and the following data. C3H8O3(l) + 3½O2(g) → 3CO2(g) + 4H2O(l) ΔH = –1654 kJ mol–1 Show your working clearly. (2)
7. The number of of carbon monoxide in a sample of air can be measured as follows. Step 1 The carbon monoxide reacts with iodine(V) oxide, producing iodine. 5CO(g) + I2O5(s) → I2(s) + 5CO2(g) Step 2 The iodine is then dissolved in potassium iodide solution and titrated against sodium thiosulphate solution. I2(aq) + 2S2O → S4O + 2I– aq) (a) Write the ion-electron equation for the oxidation reaction in Step 2. (1) (b) Name a chemical that can be used to indicate when all of the iodine has been removed in the reaction taking place in Step 2. (1) (c) If 50.4cm3 of 0.10 mol l–1 sodium thiosulphate solution was used in a titration, calculate the number of moles of carbon monoxide in the sample of air. Show your working clearly. (2) 8. A major problem for the developed world is the pollution of rivers and streams by nitrite and nitrate ions. The concentration of nitrite ions, NO2 –(aq), in water can be determined by titrating samples against acidified permanganate solution. (a) Suggest two points of good practice that should be followed to ensure that an accurate end-point is achieved in a titration. (b) An average of 21·6cm3 of 0·0150 mol l–1 acidified permanganate solution was required to react completely with the nitrite ions in a 25·0 cm3 sample of river water. The equation for the reaction taking place is: – – + 2+ – 2MnO4 (aq) + 5NO2 (aq) + 6H (aq) → 2Mn (aq) + 5NO3 (aq) + 3H2O(l) (i) Calculate the nitrite ion concentration, in mol l–1, in the river water. Show your working clearly. (2) (ii) During the reaction the nitrite ion is oxidised to the nitrate ion. Complete the ion-electron equation for the oxidation of the nitrite ions. – – NO2 (aq) → NO3 (aq) (1)