问题 计算题

某课外活动小组为测定当地石灰石中含碳酸钙的质量分数,取来了一些矿石,准确称取25g放于盛有200g稀盐酸(氯化氢的水溶液)的烧杯中(杂质不溶于水,也不与稀盐酸反应,也不分解),恰好完全反应。测得烧杯内物质的总质量与时间的关系如图所示(溶解的气体忽略不计)。

试计算:

(1)生成二氧化碳的质量是    _; 

(2)所用稀盐酸的溶质质量分数是多少?  

(3)石灰石中碳酸钙的质量分数是多少?

答案

(1)8.8g;(2)7.3%;(3)80%

题目分析:(1)生成二氧化碳的质量是8.8g;

(2)解:设稀盐酸中的溶质质量为X,石灰石中碳酸钙质量为Y

CaCO3+2HCl=CaCl2+H2O+CO2↑   

100    73           44

Y     X            8.8g

8.8g︰44  =  X︰73 =  Y︰100

X = 14.6g    Y = 20g         

所用稀盐酸的溶质质量分数="14.6g/200g" x 100% ="7.3%"  

(3)石灰石中碳酸钙的质量分数=" 20g/25g" x 100% =80%)

答:所用稀盐酸的溶质质量分数为7.3%;石灰石中碳酸钙的质量分数为80%。

单项选择题
阅读理解

阅读理解。

     People believe that climbing can do good to health. Where can you learn the skill of climbing then? If you

think that you have to go to the mountains to learn how to climb, you're wrong. Many Americans are learning

to climb in city gyms (体育馆). Here, people are learning on climbing. The climbing wall goes straight up and

small holding places for hands and feet.

     How do people climb the wall? To climb, you need special shoes and (保护带) around your chest to hold

you. There are ropes (绳索) tied to your. The ropes hold you in place so that you don't fall. A beginner's wall

is usually about 15 feet high, and you climb straight up. There are small pieces of metal that stick out for you

to stand on and hold on to. Sometimes it's easy to see the new piece of metal. Sometimes, it's not. The most

difficult is an your fear. It's normal for humans to be afraid of falling, so it's difficult not to feel fear. But when

you move away from the wall, the and the ropes hold you, and you begin to feel safe. You move slowly until

you reach the top.

     Climbing attracts people because it's good exercise for almost everyone. You use your whole body,

especially your arms and legs. This sport gives your body a complete workout. When you climb, both your

mind and your body can become stronger.

1. What can we infer from the passage?

A. People are fairly interested in climbing nowadays.

B. It is impossible to build up one's body by climbing.

C. People can only learn the skill of climbing outdoors.

D. It is always easy to see holding places in climbing.

2. The most difficult thing to do in wall climbing is _____.

A. to tie ropes to your

B. to control your fear

C. to move away from the wall

D. to climb straight up

3. The word "workout" underlined in the last paragraph most probably means _____.

A. settlement

B. exercise

C. excitement

D. tiredness

4. Why does the author write this passage?

A. To tell people where to find gyms.

B. To prove the basic need for climbing.

C. To encourage people to climb mountains.

D. introduce the sport of wall climbing.