问题 问答题

为了测定某铜锌合金(即铜锌混合物)中锌的质量分数,某同学利用该合金与稀硫酸反应,进行了三次实验,所得相关的实验数据记录如下(实验中的误差忽略不计):

 第一次第二次第三次
所取合金的质量/g252525
所用稀硫酸的质量/g80120160
生成氢气的质量/g0.30.40.4
(1)第一次产生氢气最少的原因是______;

(2)后两次产生氢气一样多的原因是______;

(3)试计算该合金中锌的质量分数.

答案

(1)所用稀硫酸的量不足,导致合金中锌未完全反应.

(2)合金中能反应的锌已反应完,两次所取合金的质量相等.

(3)设该合金中锌的质量为 X.  

Zn+H2SO4═ZnSO4+H2

65               2 

X              0.4g

65
2
x
0.4g
,x=13g

13g÷25×100%═52%

答:合金中锌的质量分数为52%.

阅读理解

阅读理解。

     We need to be responsible for our environment. Being a frugal consumer (节俭的消费者) is one way

to help. But, what exactly does that mean?   

     Use It Up   

     You can use things up instead of wasting them. Squeeze that last bit of toothpaste out of the tube. Use

the last little piece of soap. Don't throw away any bits of the biscuit at the bottom of the box.   

     Wear It Out   

     You do not always need to have new things. Suppose your sneakers have broken laces, but they still

fit you. Repair them and wear them longer. You don't have the latest iPhone until the old one doesn't work

anymore. Then you can get a new one. Think twice before replacing something that still works.   

     Make It Do   

     When something you want is not on hand, look for something else that you already have to take its place.

Suppose you are packing your lunch for tomorrow and want a butter sandwich. You are out of butter. Have

a cheese sandwich instead so that you can use all of the cheese. Learn to fix broken toys instead of just

throwing them away. With a little thought, you can make something do, instead of buying something new.   

     Do Without   

     Think about all those things that you would like to have. Do you really need them? How long will you

really play with that new toy you saw on TV? Making the things that we want uses up your world's resources(资源). And, getting rid of the things we don't want any more takes up even more resources and space.

1. Do we need to be responsible for our environment?  

    __________________________________________________ 

2. How do we deal with the last little piece of soap?  

    __________________________________________________  

3. When do we need to get a new iPhone?

    __________________________________________________ 

4. What should we do when something we want is not on hand? 

    __________________________________________________ 

5. What does the writer want to tell us?

    __________________________________________________ 

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