问题 填空题

为了除去粗盐配制成的NaCl溶液中所含有的少量MgCl2,CaCl2和MgSO4杂质,某同学从碳酸钠溶液、稀盐酸、硝酸钡溶液、碳酸钾溶液和氢氧化钡溶液中选择了A、B、C三种试剂,按以下步骤进行了实验:

实验Ⅰ:向溶液中加入过量A后过滤得到滤液1;

实验Ⅱ:向滤液1中加过量B后过滤得到滤液2;

实验Ⅲ:向滤液2中加适量C,得到较纯净的NaCl溶液.

请回答下列问题:

①A、B、C三种试剂中溶质的化学式分别为______

②实验I中,所加A要过量的原因______

③实验II中,所加B要过量的原因______

④实验Ⅲ中,试剂加到______时为适量,此时得到较为纯净的NaCl溶液.

答案

(1)要除去MgCl2、CaCl2和MgSO4杂质,就是除去Mg2+、Ca2+和SO42-,可以分别选用OH-、CO32-和Ba2+除去,选择的除杂试剂与杂质反应时要求不能生成新的杂质,后加的试剂能将上一步过量的试剂反应掉,可以选用的物质分别是氢氧化钡、碳酸钠、以及盐酸,所以本题答案为:Ba(OH)2、Na2CO3、HCl;

(2)为了充分除去Mg2+和SO42-,需要加入过量的氢氧化钡,氢氧化钡能与氯化镁反应生成氢氧化镁沉淀和氯化钡,硫酸镁能与氢氧化钡反应生活硫酸钡沉淀和氢氧化镁沉淀,所以本题答案为:为了除尽MgCl2、MgSO4

(3)为了除去Ca2+和上一步过量的钡离子,需要加入过量的碳酸钠,碳酸钠能与氢氧化钡反应生成碳酸钡沉淀和氢氧化钠,能与氯化钙反应生成碳酸钙沉淀和氯化钠,能与氯化钡反应生成碳酸钡沉淀和氯化钠,所以本题答案为:为了除尽Ba(OH)2、CaCl2、BaCl2

(4)经过实验Ⅰ和实验Ⅱ,食盐中还含有的杂质是氢氧化钠和碳酸钠,此时可以加入盐酸将多余的氢氧化钠和碳酸钠除掉,碳酸钠能与盐酸反应生成二氧化碳气体,当完全反应时无气泡产生,所以本题答案为:刚好无气体放出.

故答案为:(1)Ba(OH)2、Na2CO3、HCl;

(2)为了除尽MgCl2、MgSO4(或答:为了除尽Mg2+、SO42-);

(3)为了除尽Ba(OH)2、CaCl2、BaCl2(或答:为了除尽Ba2+、Ca2+);

(4)刚好无气体放出时(或答:用酚酞检验,红色刚刚褪去时).

单项选择题 A1型题
单项选择题

Being a good parent is harder now than it has ever been before. In pressurised modern lives, demands to be a fulfilled individual, and a good partner and a good worker, take no account of being a good parent. We haven’t left space for the nurturing parents expect to provide and children need. As a result, many parents in the western world just don’t work.

Something will have to change. With luck, people in the future will only have children if they really want them And that should mean that parenthood is seen as a much more positive commitment than it is now, and that parents are socially supported, and admired for doing a good job.

The problem is that in the last generation or so we’ve come to assume that women should be able, and should want, to do everything that by tradition men have done at the same time as pretty well as everything that by tradition women have done. And it’s just not possible. Indeed since adopting a male agenda in life is arguably only another form of submission (男尊女卑), quite a number of highly educated and economically privileged women are now choosing to take career breaks so as to be at home with their children for longer than that insulting 18 weeks*.

The most welcome trend in parenting is that men are participating more and more. Even that is not free of conflict, though. Intellectually, women want men to be equal parents and do their share. But there’s often a contradictory emotional sub-text because children are the last bastion (堡垒) of distaff power (女性的权利) in the family. "I want him to help me but this is my territory and being better at it is one of the few things I’ve got as a female. "

Having children—especially the first child—puts a bigger strain on a couple’s relationship than anything else they ever do. So a future of smaller families and more people choosing not to have children at all could well leave couples closer than they are today; for many, the purpose of being together would be solely to pleasure and support each other-an interesting prospect.

*在英国,妇女的法定产假是18周。

It is assumed by the last generation or so that ().

A. women should stay home while men go out to work

B. women should go out to have their own careers

C. women should be able and willing to do the housework and hold a job at the same time

D. women and men should equally share the housework and have equal opportunities at work