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【简答题】
(12分)某同学为了探究锌与硫酸反应过程中的速率变化，他在100mL稀硫酸中加入足量的锌粉，标用排水集气法收集反应放出的氢气，实验记录如下(累计值)： 时间(min) 1 2 3 4 5 氢气体积(mL)(标准状况) 50 120 232 290 310 (1)哪一时间段(指0～1、1～2、2～3、3～4、4～5min)反应速率最大______________，原因是______________________________________________。 (2)哪一时间段的反应速率最小________________，原因是___________________。 (3)求2～3分钟时间段以硫酸的浓度变化来表示的该反应速率(设溶液体积不变，要写出计算过程)______________________________________________________。 (4)该同学在用稀硫酸与锌制取氢气的实验中，发现加入少量硫酸铜溶液可加快氢气的生成速率。请回答下列问题： ①上述实验中涉及到的离子反应方程式有 ； ②硫酸铜溶液可以加快氢气生成速率的原因是 ； ③实验室中现有Na 2 SO 4 、MgSO 4 、Ag 2 SO 4 、K 2 SO 4 等4种溶液，可与实验中CuSO 4 溶液起相似作用的是 ； ④该同学通过实验进一步研究了硫酸铜的量对氢气生成速率的影响。该同学最后得出的结论为：当加入少量CuSO 4 溶液时，生成氢气的速率会大大提高。但当加入的CuSO 4 溶液超过一定量时，生成氢气的速率反而会下降。请分析氢气生成速率下降的主要原因 。
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