CAPE Chemistry Unit 2 · 2007 · Paper 2

61 questions and parts from this paper. Open one to see it in full, then practise it on Quelpr and get it marked against the mark scheme.

1. 1(a)(i)1 markWrite the chemical equation for the equilibrium reaction between bromine and chlorine forming BrCl.
2. 1(a)(ii)2 marksWrite the expression for the equilibrium constant, K_c.
3. 1(b)(i)3 marksIn an experiment to monitor the equilibrium, the mixture contains 0.0389 mol of Br2, 0.0111 mol of Cl2, and 0.0546 mol of BrCl. Given that K_c at 298 K is 6.88, determine whether equilibrium has been attained in the…
4. 1(b)(ii)2 marksState TWO precautions that should be taken to ensure the experiment yields accurate results.
5. 1(b)(iii)1 markSuggest ONE safety measure that should be taken in this experiment.
6. 1(c)1 markUnder what experimental condition would the value of K_c be greater than 6.90, given that the reaction is endothermic?
7. 2(a)5 marksComplete Table 1 by filling in the missing reaction products and observations: (i) reaction product for NaCl, (ii) reaction product for NaBr, (iii) observation for SO2, (iv) reaction product for NaI, and (v) observation…
8. 2(b)1 markSuggest ONE reason for the differences in physical states among chlorine (gas), bromine (liquid), and iodine (solid) at room temperature and pressure.
9. 2(c)4 marksWrite a balanced equation for the reaction of chlorine with an excess of cold dilute sodium hydroxide, and state the change in oxidation state of chlorine in the reaction.
10. 3(a)(i)1 markSuggest ONE possible source of phosphate ions found in polluted rivers and lakes.
11. 3(a)(ii)1 markWhat observable feature of a polluted lake could result from phosphate concentrations above 1.0 mg dm^-3?
12. 3(a)(iii)1 markWhat process is responsible for the observed feature resulting from high phosphate levels?
13. 3(b)(i)4 marksUsing the calibration curve of absorbance versus concentration provided in Figure 1, estimate the concentration of phosphate ion in each sample and complete Table 2.
14. 3(b)(ii)2 marksCalculate the average concentration of PO4^3- found in the three samples.
15. 3(b)(iii)1 markBased on the results of the analysis, determine whether the concentration of PO4^3- is within acceptable limits.
16. 4(a)2 marksDefine the term 'buffer solution'.
17. 4(b)(i)3 marksExplain how a buffer mixture of a weak acid and its salt maintains pH upon the addition of strong acid.
18. 4(b)(ii)3 marksExplain how a buffer mixture of a weak acid and its salt maintains pH upon the addition of strong alkali.
19. 4(c)(i)(a)2 marksDuring periods of strenuous exercise, carbon dioxide builds up in the blood. Explain the effect of this build-up on the buffer system with reference to Equations 1 and 2.
20. 4(c)(i)(b)4 marksExplain how breathing more deeply and quickly during exercise can reverse this effect.
21. 4(d)(i)1 markWrite the expression for K_a of ethanoic acid.
22. 4(d)(ii)5 marksUse the K_a expression to calculate the pH of the buffer solution.
23. 5(a)(i)2 marksDetermine the order of the hydrolysis reaction with respect to R-X using Table 3.
24. 5(a)(ii)2 marksDetermine the order of the hydrolysis reaction with respect to NaOH using Table 3.
25. 5(b)2 marksDeduce the overall order of the reaction and construct the rate equation for the hydrolysis.
26. 5(c)3 marksCalculate the value of the rate constant and state its units.
27. 5(d)3 marksSuggest a possible mechanism for the hydrolysis of the primary halogenoalkane and use the representative structure to illustrate the steps involved.
28. 5(e)(i)3 marksUse collision theory to state and explain the effect of temperature on the rate of a reaction.
29. 5(e)(ii)3 marksUse collision theory to state and explain the effect of concentration on the rate of a reaction.
30. 5(e)(iii)2 marksUse collision theory to state and explain the effect of surface area on the rate of a reaction.
31. 6(a)6 marksComplete Table 4 by stating the type of bonding present in Na2O, MgO, Al2O3, AlCl3, SiCl4, and PCl5.
32. 6(b)(i)1 markState the acid/base character of MgO.
33. 6(b)(ii)1 markState the acid/base character of Al2O3.
34. 6(c)(i)2 marksWrite a balanced equation for the reaction of Na2O with water.
35. 6(c)(ii)2 marksWrite a balanced equation for the reaction of SiCl4 with water.
36. 6(c)(iii)2 marksWrite a balanced equation for the reaction of PCl5 with water.
37. 6(d)2 marksGive the approximate pH of the solution formed from the reactions in (c)(i) and (c)(ii).
38. 6(e)4 marksExplain why SiCl4 is a liquid at room temperature and pressure whereas SiO2 is a solid with a high melting point, in terms of structure and bonding.
39. 7(a)2 marksDescribe the trend in electrical conductivities of Group IV elements and relate it to their physical structure.
40. 7(b)(i)1 markState the type of bonding found in CO2.
41. 7(b)(ii)1 markState the type of bonding found in SiO2.
42. 7(b)(iii)1 markState the type of bonding found in GeO2.
43. 7(b)(iv)1 markState the type of bonding found in PbO2.
44. 7(c)4 marksClassify the acid/base character of the Group IV dioxides and explain how it relates to the type of bonding.
45. 7(d)2 marksUse the provided standard electrode potentials to comment on the relative stability of the +4 and +2 oxidation states of Ge, Sn, and Pb.
46. 7(e)4 marksExplain why Sn2+ ions will reduce orange Cr2O7^2- to green Cr3+ but Pb2+ ions will not, referencing standard electrode potentials and using suitable half-equations.
47. 7(f)4 marksExplain why silicon tetrachloride (SiCl4) fumes and forms a white precipitate with water while carbon tetrachloride (CCl4) is immiscible with water, and write a balanced equation for the reaction occurring.
48. 8(a)(i)1 markState the name of the process used to separate crude oil into its various fractions.
49. 8(a)(ii)2 marksExplain the physical basis on which the fractional separation of crude oil occurs.
50. 8(b)(i)6 marksExplain how NO2 and SO2 are produced during the combustion of fossil fuels, illustrating with balanced equations.
51. 8(b)(ii)2 marksState the environmental implications of releasing NO2 and SO2 into the atmosphere.
52. 8(c)(i)2 marksExplain why leaded compounds and carbon monoxide are considered pollutants.
53. 8(c)(ii)2 marksExplain the source of PbO and carbon monoxide in vehicular exhaust.
54. 8(c)(iii)1 markState ONE step taken to reduce the amount of lead pollution caused by vehicle fuel.
55. 8(d)4 marksSuggest FOUR considerations that must be taken into account when choosing the location of an oil refinery.
56. 9(a)(i)6 marksWrite equations showing the formation of stratospheric ozone and how ozone levels are maintained naturally in the stratosphere.
57. 9(a)(ii)3 marksExplain the biological significance of stratospheric ozone.
58. 9(b)4 marksGive FOUR reasons why ozone is considered a pollutant in the troposphere (lower atmosphere).
59. 9(c)(i)3 marksState THREE properties that made CFCs suitable for use as aerosol propellants.
60. 9(c)(ii)2 marksState TWO other uses of CFCs or Freons.
61. 9(d)2 marksGive TWO reasons why CFCs are so destructive to the stratospheric ozone layer.