实验室用100g氯酸钾催化加热制氧气，加热一段时间后称量剩余固体_爱下问搜题

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问题选择题

实验室用100g氯酸钾催化加热制氧气，加热一段时间后称量剩余固体96.8g，则此时剩余固体为哪些成分（　　）

A．KClO₃、KCl、MnO₂

B．KClO₃、KCl

C．KClO₃、MnO₂

D．KCl、MnO₂

答案

由题意和一般的实验规律可知，100g反应前的物质中一定含有催化剂MnO₂，并且其质量大约为25g（即100g×

1

3+1

；因为氯酸钾和二氧化锰一般是按照质量比为3：1比例混合的）；而氯酸钾的质量大约为75g．

根据质量守恒定律得，反应生成的氧气的质量为：100g-96.8g=3.2g；

设反应的KClO₃和生成的KCl的质量分别为x、y；

2KClO₃

MnO2

.

△

2KCl+3O₂↑

245 149 96

x y 3.2g

245

96

=

x

3.2g

；

149

96

=

y

3.2g

x=8.17g； y=4.97g．

由于8.17g远小于75g，所以反应后剩余固体中有KClO₃；

并且，还含有KCl、MnO₂．

因此，A选项是正确的，其余的都不对．

故选A．

单项选择题

The first time I remember noticing the crossing guard was when he waved to me as I drove my son to school. He (31) me with a puzzle-all because he waved to me like someone does on seeing a close friend. A big, (32) smile accompanied his wave. For the next few days I tried tO study his face to see if I knew him. I didn’t. Perhaps he had (33) me for someone else. By the time I contented myself with the conclusion that he and I were strangers, we were greeting each other warmly every morning like old friends.

Then one day the (34) was solved. As I approached the school he was standing in the middle of the road (35) his stop sign. I was in live behind four cars. Once the kids had reached the safety of the sidewalk, he lowered his sign and let the cars (36) . To the first he waved and smiled in just the same way he had done to me over the last few days. The kids already had the window down and were happily waving their reply. The second car got the same (37) from the crossing guard, and the driver, a stiff-looking businessman, gave a brief, almost awkward wave back. Each following car of kids on their way to school (38) more heartily.

Every morning I continued to watch the man with interest. So far I haven’t seen anyone (39) to wave back. I find it interesting that one person can make such a difference to so many people’s lives by doing one simple thing like waving and smiling warmly. His (40) armed the start of my day. With a friendly wave and smiling fade he had changed the feelings of the whole neighbourhood.

35（）。

A. drawing back

B. putting on

C. handing in

D. holding out

填空题

着墨压力（），图案墨层变薄，印出的图案缺少立体感。