问题 问答题

小明同学为测定某铜锌合金的组成,取10g该合金经粉碎后放入烧杯中,然后加入100g溶质质量分数为20%的过量的稀硫酸,充分反应后烧杯中剩余物质总质量为109.8g.试回答下列问题:

(1)写出加入稀硫酸的过程中观察到的一项实验现象______.

(2)实验过程中,小红同学提出了一个观点:“反应前后,烧杯中物质的总质量发生了变化,所以此反应不符合质量守恒定律”.你认为她的观点正确吗?______(填“正确”“不正确”之一),简述你的理由______.

(3)试通过计算,求最后所得溶液的质量(写出相应计算过程,结果精确到0.1g).

答案

(1)铜锌合金中的锌可以和稀硫酸反应,所以能够观察到气体生成,固体减少;

(2)该反应中生成了氢气,而氢气逸散到空气中没有称量,所以不能仅仅根据表面现象来判断该反应不符合质量守恒定律,所以小红的观点不正确;

(3)根据质量守恒定律,由题意可知反应中生成氢气的质量:10g+100g-109.8g=0.2g;

设铜锌合金中锌的质量为x

Zn+H2SO4═ZnSO4+H2↑  

65              2

x             0.2g

65
x
=
2
0.2g

解得:x=6.5g     

反应后所得溶液的质量为:6.5g+100g-0.2g=106.3g 

答:最后所得溶液的质量为106.3g

故答案为:(1)固体减少,生成气体;

(2)不正确;产生的气体散失到空气中;

(3)106.3g.

阅读理解

阅读理解。

     Can dolphins talk? Maybe they can't talk with words, but they talk with sounds.

     Dolphins travel in a group.  We  call  a  group  of  fish  a  "school". They don't study but they travel

together. Dolphins are mammals, not fish, but they swim together in a school.

     Dolphins talk to other dolphins in the school. They give information. They tell when they are happy

or sad or afraid. They say welcome when  a  dolphin  comes  back to the school. They talk when they

play.

     They make a few sounds above  water. They make many more sounds  under  water. People can't

hear these sounds because they are very high.   Scientists make tapes of the  sounds  and  study .them,

Sometimes people catch a dolphin for a large aquarium(水族馆). People watch the dolphins in a show.

Dolphins don't like to  be  away from  their school. In  the aquarium they are sad and lonely.  There are

many stories about dolphins.  They  can help people.  Sometimes  they save  somebody's  life.  Dolphin

meat is good but people don't like to kill them. They say that dolphins bring good luck. Many people

believe this.

1. Dolphins can talk with _________.              

A. sounds              

B. words

C. language              

D. action  

2. Dolphins________ be in their school.  

A. don't like to          

B. like to

C. liking                

D. likes

3. Dolphins always bring ___________.

A. sadness            

B. wishes

C. bad luck          

D. good luck             

4. Dolphins make ___________ sounds above water.

A. more              

B. many   .

C. a few              

D. much

5.Which of the following is TRUE? 

A. Dolphin meat is good, so people like to kill them.

B. Sometimes dolphins save somebody's life.

C. Dolphins make a few sounds under water.

D. People can hear these sounds.from under water.

多项选择题