问题 问答题 简答题

重铬酸钾法中用试亚铁灵做指示剂时,为什么常用亚铁离子滴定重铬酸钾,而不是用重铬酸钾滴定亚铁离子?

答案

参考答案:重铬酸钾法用试亚铁灵做指示剂的原理是:滴定过程中,被滴定化合物重铬酸钾被滴定剂亚铁离子还原,终点时因亚铁离子过量,与试亚铁灵反应生成红色化合物指示终点。所以只能用亚铁离子滴定重铬酸钾,否则用重铬酸钾滴定亚铁离子,就不能用试亚铁灵做指示剂。

完形填空

I met the guy who told me an amazing story.He was  21  Scotland on a motorbike by himself.One late afternoon he was on the road between Aberdeen and Elgin.He was travelling along, miles from any village, when he saw a really  22  girl standing by the road, hitchhiking (搭便车).Anyway, he stopped and said he would give her a  23  to Elgin.She got and drove off.He said he  24 having her on the back,  as it was nice   25.But after a time he forgot that she was there.Suddenly he  26 but he realized that he couldn’t feel her knees  27 against him ! He  28 behind him but …she wasn’t there.

He said he felt frightened  29 his life ! He felt cold all over.He thought she must have 30 off the back.So he turned round and 31 back along the road.He didn’t find her.So he began to think that she might have been 32 by someone else.

Anyway, he drove on towards Elgin and didn’t see anyone  33 he came to a pub.He decided to 34 so that he could talk to someone and he thought he ought to tell  35  .He went into the pub and talked to the barman.He told the barman what had happened.He said the barman didn’t seem to be at all  36 .He just carried on  37 the glasses.

Then the barman said, “you are not the  38 person to come in here and tell the same  39.That girl you think you picked up  40 seven years ago… in a motorbike accident.”

21.A.touring                B.searching                  C.defending        D.circling

22.A.poor              B.attractive          C.tall              D.terrible  

23.A.help                      B.lift               C.service           D.trip 

24.A.chose              B.came              C.meant            D.liked 

25.A.business           B.event             C.company          D.action

26.A.thought           B.considered         C.remembered       D.called

27.A.pressing           B.turning           C.going            D.running

28.A.looked             B.took              C.felt              D.seized

29.A.out of             B.in case of          C.in place of       D.to the best of

30.A.jumped            B.kept              C.kicked            D.fallen

31.A.raced              B.walked            C.got              D.watched

32.A.picked up          B.searched for       C.taken away       D.brought back

33.A.when              B.until              C.although         D.since

34.A.wait               B.enter             C.stop              D.march

35.A.someone           B.nobody           C.the father          D.the police

36.A.worried           B.surprised          C.moving            D.satisfied

37.A.breaking           B.waving           C.knocking          D.drying

38.A.first               B.last               C.right             D.honest

39.A.story              B.message           C.lie               D.truth

40.A.was saved          B.ran away          C.died              D.left

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