问题 问答题

将15g锌铜混合物与100g稀硫酸恰好完全反应,生成氢气0.4g,求:

(1)混合物中锌的质量是多少?

(2) 所用的100g稀硫酸中水的质量是多少?稀硫酸溶液中溶质的质量分数是多少?

(3)反应后所得溶液中溶质的质量分数又是多少?

答案

设生成0.4g氢气消耗锌的质量为z,消耗硫酸的质量为y,反应后生成硫酸锌的质量为x

Zn+H2SO4=ZnSO4+H2

65  98   161  2

z   y     x  0.4g

161
x
=
2
0.4g
  x=32.2g

98
y
=
2
0.4g
  y=19.6g

65
z
=
2
0.4g
  z=13g

所用的100g稀硫酸中水的质量=100g-19.6g=80.4g

稀硫酸溶液中溶质的质量分数=

19.6g
100g
×100%=19.6%

反应后所得溶液中溶质的质量分数=

32.2g
13g+100g-0.4g
×100%≈28.6%

答:(1)混合物中锌的质量是13g;

(2) 所用的100g稀硫酸中水的质量是80.4g;稀硫酸溶液中溶质的质量分数是19.6%;

(3)反应后所得溶液中溶质的质量分数28.6%.

选择题
阅读理解

When I come across a good essay in reading newspapers,I am often inclined to cut and keep it.But just as I am about to do so I find the article on the opposite side is as much interesting.It may be a discussion of the way to keep in good health,or advice about how to behave and conduct oneself in society.If I cut the front essay,the opposite one is bound to suffer damage,leaving out half of it or keeping the text without the subject.As a result,the scissors would stay before they start,or halfway done when I find out the regretful consequence that inevitably(不可避免地) causes my repentance.   

Sometimes two things are to be done at the same time,both deserving your attention.You can only take up one of them,the other has to wait or be given up.But you know the future is unpredictable—the changed situation may not allow you to do what is left behind.Thus you are caught in a fix and feel sad.How come that nice opportunities and brilliant ideas should gather around all at once?It may happen that your life changes dramatically on your preference of one alternative to the other.

In fact that is what life is like:we are often faced with the two opposite aspects of a thing which are both desirable like newspaper cutting.It often occurs that our attention is drawn to one thing only after we are engaged in another.The former may be more important than the latter and give rise to a divided mind.I still remember a philosopher’s remarks:“When one door shuts,another opens in life.” So a casual or passive choice may not be a bad one.

Whatever we do in our lifetime,wherever life’s storm tosses us,there must be something we can achieve,some shore we can land,that opens up new vistas to us.Don’t forget God always keeps an alternative door open for every one.While the front door is closed,there must be another open for you.

小题1:When the writer finds a good article in reading newspapers,______.

A.he is always glad to cut and keep it

B.he is always hesitant to cut and keep it

C.he often has a desire to cut and keep it

D.he often finds it difficult to decide which side to cut and keep小题2:The writer feels regretful because______.

A.he fails to choose a good essay

B.he fails to cut the two essays on both sides well

C.he finds the essay on the opposite side is better

D.he finds that he just keeps the text without the subject小题3:What’s the meaning of the underlined part in Paragraph 2?

A.You’re trapped in a trouble.

B.You find it difficult to fix something.

C.You are trapped in a situation where you can’t decide which choice is better.

D.You have so many opportunities that you don’t know which to choose.小题4:Which one do you think is the best title of this passage?

A.Paper Cutting

B.Two Opposite Sides

C.Difficult Choices

D.Another Door