问题 问答题

已知实验室制氯气的化学方程式为:MnO2+4HCl (浓)=MnCl2+Cl2↑+2H2O,现用足量浓盐酸在加热条件下跟二氧化锰反应制取氯气.若标准状况下制得Cl22.24L求:

(1)二氧化锰的质量;

(2)把(1)中反应后的溶液稀释到50mL,从中取出10.0mL,加入10.0mL 0.600mol/L的硝酸银溶液,恰好将氯离子完全沉淀.求(1)中反应后溶液稀释到50mL时氯离子的物质的量浓度是多少?

答案

(1)n(Cl2)=

2.24L
22.4L/mol
=0.1mol,

MnO2+4HCl (浓)=MnCl2+Cl2↑+2H2O

1                      1

n(MnO2)                0.1mol

n(MnO2)=0.1mol,

m(MnO2)=0.1mol×87g/mol=8.7g,

答:二氧化锰的质量为8.7g;

(2)n(AgNO3)=0.01L×0.600mol/L=0.006mol,

由反应Ag++Cl-=AgCl↓可知:10.0ml溶液中:n(Cl-)=n(AgNO3)=0.006mol,

则50ml溶液中含有的Cl-物质的量为:0.006mol×5=0.03mol,

所以:(1)中反应后溶液稀释到50mL时氯离子的物质的量浓度是:c(Cl-)=

0.03mol
0.05L
=0.6mol/L,

答::(1)中反应后溶液稀释到50mL时氯离子的物质的量浓度是0.6mol/L.

阅读理解

阅读理解。

     When my son, Mark, was in the third grade, he saved all his pocket money for over three months to buy

holiday presents. The third Saturday in December Mark said he had made his list and had twenty dollars in his

pocket.

     I drove him to a nearby supermarket. Mark picked up a hand basket and went in while I waited and

watched in the car. It took Mark over 45 minutes to choose his presents. Finally he came to the checkout

counter (交款处) and reached into his pocket for his money. It was not there! There was a hole in his pocket,

but no money. Mark stood there holding his basket, tears falling down his face.

     Then a surprising thing happened. A woman came up to Mark and took him in her arms."You would help

me a lot if you let me pay for you," said the woman."It would be the most wonderful gift you could give me.

I only ask that one day you will pass it on. When you grow up, I would like you to find someone you can help.

When you help others, I know you will feel as good about it as I do now."

     Mark took the money, dried his tears and ran back to the checkout counter as fast as he could. That year

we all enjoyed our gifts almost as much as Mark enjoyed giving them to us.

     I would like to say "thank you" to that very kind woman, and tell her that four years later, Mark went house

to house collecting blankets (毯子) and clothes for the homeless people in the fire. And I want to promise her

that Mark will never forget to keep passing it on.

1. When did the story probably happen?

A. On Christmas Day.

B. Before Christmas Day.

C. On New Year's Day.

D. After New Year's Day.

2. When they got to the supermarket, Mark went in .

A. with the writer

B. by himself

C. with the woman

D. with his friends

3. What happened to Mark in the supermarket?

A. His gifts were stolen.

B. He broke his basket.

C. He lost his money.

D. He lost his way.

4. Why did the writer want to say "thank you" to the woman?

A. Because she bought Mark a nice present.

B. Because she always paid money for others.

C. Because she collected clothes for the homeless.

D. Because she taught Mark to help people in need.

5. What's the best title for this passage?

A. A big supermarket

B. A kind woman

C. A happy family

D. A wonderful gift

单项选择题