试题与答案

重庆市黔江区有一保存比较完好的地质公园,其“小南海”水下公园是古代某一村庄因地震

题型:问答题

题目:

重庆市黔江区有一保存比较完好的地质公园,其“小南海”水下公园是古代某一村庄因地震而下沉形成,风景优美,水中暗藏秘密.潜水员潜入深水区进行探测作业时需要携带供氧等设备.供氧设备中有种供氧剂(用R表示,R为纯净物)能与二氧化碳或水接触产生氧气.现将7.8g R投入73.8g 水中,充分反应后得到80g溶液.请回答:

(1) 反应方程式2R+2H2O═4NaOH+O2↑中R的化学式为______;理论上产生氧气的质量为______克.

(2) 计算反应后所得溶液的溶质质量分数(写出计算过程).

答案:

(1)根据反应方程式2R+2H2O═4NaOH+O2↑,反应后所有生成物的粒子中共含有Na、H、O三种元素的原子个数分别为4、4、6,而反应物水的2个分子中只含有4个H原子和2个O原子,所以在物质R的2个分子中应含有4个Na原子和4个O原子,物质R的化学式可表示为Na2O2

根据质量守恒定律,理论上产生氧气的质量=73.8g+7.8g-80g=1.6g

故答案为:Na2O2 ;1.6;

(2)设生成氢氧化钠的质量为x

2Na2O2+2H2O═4NaOH+O2

156          160

7.8g          x

156
7.8g
=
160
x
 

解得:x=8g

反应后所得溶液溶质质量分数=

8g
80g
×100%=10%

答:反应后所得溶液的溶质质量分数为10%.(其它计算过程合理也可给分)

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     We know the mosquito very well. Mosquitoes fly everywhere. They can be found almost all over the world, and there are more than 2,500 kinds of them.

     No one likes the mosquito. But the mosquito may decide that she loves you. She? Yes, she. It's true that

male mosquito doesn't bite and only the female mosquito bites because she needs blood to lay eggs. She is

always looking for things or people she wants to bite. If she likes what she finds, she bites. But if she doesn't

like your blood, she will turn to someone else for more delicious blood. Next time a mosquito bites you, just

remember you are chosen. You're different from the others!

     If the mosquito likes you, she lands on your body without letting you know. She bites you so quickly and

quietly that you may not feel anything different. After she bites, you will have an itch (痒) on your body

because she puts something from her mouth together with your blood. By the time the itching begins, she has

flown away. 

     And then what happens? Well, after her delicious dinner, the mosquito feels tired. She just wants to find a

place to have a good rest. There, on a leaf or a wall, she begins to lay eggs, hundreds of eggs.

1. In which part of a magazine can you probably read this article?

A. Science World.

B. News Report.

C. Sports Square.

D. Culture Corner.

2. When a mosquito decides that she doesn't like your blood, she will  ______.

A. land on your body

B. feel very tired soon

C. choose another one instead

D. find a different kind of food

3. The mosquito bites you ______.

A. in order to have a good rest

B. too quickly to let you know

C. only if you're female

D. when she gets angry with you

4. Why do you have an itch after the mosquito bites you?

A. Because she drinks too much.

B. Because she bites so quietly.

C. Because she lays eggs in your blood.

D. Because she puts something special into your blood.

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