標題:
問CHEM 2000 MC Q.38 and q.44
發問:
問CHEM 2000 MC Q.38 and q.44 可唔可以解釋下個答案問黎?
最佳解答:
38. The answer is A. For B and C, plastic is used nowadays because they are endurant to acid and alkalis. Therefore, decomposition of PVC plastic and oxidation of PVC is not the reason. The only reason is A. Because adding sulphuric acid into water is highly exothermic, some mist may evolved. (Very hot!!!) (As taught in the chapter sulphuric acid). As PVC is a thermoplastic, so it can be softened or distorted easily by heat. 44. The answer is D. (1), (2) and (3). For (1), consider the following equation. Cu (s) + 2H2SO4 (l) → CuSO4 (aq) + SO2 (g) + 2H2O (l) So, sulphur dioxide is produced and prepared. For (2), it is a fact that sulphur dioxide is denser than air. It is the physical property of SO2. For (3), SO2 is absorbed by sodium hydroxide solution. SO2 dissolves in water to give H+ and SO4 2-. So, acid and alkail react with each other to give salt and water only (neutralization). SO2 (g) + 2H2O (l) → 4H+ (aq) + SO4 2- (aq) + 2e- Then, H2SO4 (aq) + 2NaOH (aq) → Na2SO4 (aq) + 2H2O (l)
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