问题 问答题

某化学实验小组要检测黄铜(铜、锌合金)中金属铜的纯度,同学们取20g黄铜样品,向其中分三次共加入15g盐酸溶液,充分反应后测得实验结果如下:

实验次数123
盐酸质量5g5g5g
氢气质量0.04gm0.02g
请计算:(1)第二次实验产生氢气的质量m______ g.

(2)黄铜(铜、锌合金)中金属铜的纯度.

答案

(1)第一次加5克盐酸生成0.04克氢气,第三次加5克的盐酸还生成了0.02克的氢气,说明第二次反应中金属是过量的,也生成0.04克氢气,故答案为:0.04g;

(2)设共生成(0.04g+0.04g+0.02g=0.1g)氢气,需金属锌的质量为x.

Zn+2HCl=ZnCl2+H2

65             2

X            0.1g

65
x
=
2
0.1g

X=3.25g

合金中铜的质量分数即纯度:

(20-3.25)
20
×100%=83.75%

答:黄铜(铜、锌合金)中金属铜的纯度为:83.75%.

阅读理解

Let children learn to judge their own work. A child learning to talk does not learn by being corrected all the time: if corrected too much, he will stop talking. He notices a thousand times a day the difference between the language he uses and the language those around him use. Bit by bit, he makes the necessary changes to make his language like other people’s. In the same way, children learning to do all the other things: they learn to do without being taught to walk, run, climb, whistle, ride a bicycle, compare their own performances with those of more skilled people, and slowly make the needed changes. But in school we never give a child a chance to find out his mistakes and correct them for himself. We do it all for him. We act as if we thought that he would never notice a mistake unless it was pointed out to him, or correct it unless he was made to. Let him work out, with the help of other children if he wants it, what this word says, what the answer is to that problem, whether this is a good way of saying or doing this or not.

If it is a matter of right answer, as it may be in mathematics or science, give him the answer book. Let him correct his own papers. Why should we teachers waste time on such routine(常规) work? Our job should be to help the child when he tells us that he can’t find the way to get the right answer. Let the children learn what all educated persons must some day learn, how to measure their own understanding, and how to know what they know or do not know.

小题1:According to the passage, the best way for children to learn things is by ________.

A.listening to skilled people’s advice

B.asking older people many questions

C.making mistakes and having them corrected

D.doing what other people do小题2:Which of the following does the writer think teachers should NOT do?

A.Give children correct answers.

B.Allow children to make mistakes.

C.Point out children’s mistakes to them.

D.Let children mark their own work.小题3:According to the writer, teachers in school should ________.

A.allow children to learn from each other

B.point out children’s mistakes whenever found

C.give children more book knowledge

D.correct children’s mistakes as soon as possible小题4:The passage suggests that learning to speak and learning to ride a bicycle are ________.

A.different from learning other skills

B.the same as learning skills

C.more important than other skills

D.not really important skills

问答题 案例分析题