问题 问答题

某同学研究在化学反应前后物质质量变化关系问题时,设计了如图所示的两个试验:

(1)为了探究化学反应前后物质质量变化关系,请你提出二点假设:①______;②______

(2)实验验证:

①将实验1装置放在托盘天平上称量,纪录数据后取下.挤压胶头滴管,(醋酸跟草木灰反应原理为:K2CO3+2CH3COOH=2CH3COOK+CO2↑+H2O)观察到的现象是______.

实验完毕,再进行称量,纪录数据.

②将实验2装置放在托盘天平上称量,纪录数据后取下.将两种溶液混合,观察到的现象是______,实验完毕,再进行称量,纪录数据.比较两次实验数据得出结论.

(3)实验结论:______.

(4)实验分析:用分子、原子的观点对结论进行解释______.

答案

(1)反应生成了二氧化碳气体,所以可猜想反应前后质量会减小;反应前后无气体参与,所以可猜想反应前后质量不变;

故答案为:反应前后质量会减小(或增大、或不变);反应前后质量不会发生变化(或增大或减小);

(2)①碳酸钾与醋酸反应放出二氧化碳,可观察到有气泡产生;二氧化碳能使澄清石灰水变浑浊;

故答案为:有气泡产生,石灰水变浑浊;

②蓝色的硫酸铜溶液与氢氧化钠溶液混合,硫酸铜与氢氧化钠发生复分解反应生成蓝色氢氧化铜沉淀,所以,观察到有蓝色沉淀生成;

故答案为:有蓝色沉淀生成;

(3)两个实验在反应前后没有气体物质逸出,因此会得到反应前后物质的总质量不变的结论;

故答案为:反应前后,各物质的总质量没有发生变化;

(4)化学变化是反应物的分子分解成原子,然后原子进行重新结合的过程,此过程中,原子种类不变、原子数目没有增减,因此反应前后物质的质量总和相等;

故答案为:在化学反应前后,原子的种类、个数都没有发生变化(或原子是化学变化中的最小粒子).

阅读理解

The Internet has become part of teenage life.There’s report on 3375 students aged from 10 to 18 in seven Chinese cities.It says that 38 percent of them believe they use the Internet often.While most of them get useful information and use the Internet to help in their studies, some are not using it in a good way.Many are playing online games too much.A few even visit Web sites they should not look at.Bad things can happen if young people spend too much time on the Internet.

In order to help young people use the Internet in a good way, a textbook on good Internet behavior has started to be used in some Shanghai middle schools this term.It uses real examples to teach students all about good ways of using the Internet.It gives useful advice such as its good to read news or find helpful information to study.Some students also make online friends.But if you are meeting a friend offline, let your parents know.

Teachers and parents all think the book is a very good idea.It will teach students how to be a good person in the online world.It will be a guide for teens to use the Internet and keep students away from bad sites.

60.The underlined word“it”means         .

A.the book    B.report    C.the Internet   D.useful information

61.From the report,about          students between 10~18 years old in the seven cities use the Internet often.

A.3 375    B.1 280    C.2 100    D.3 000

62.What do most of the students do on the Internet?

A.To make online friends.

B.To play online games.

C.To get useful information to help in their studies.

D.To visit Web sites they should not look at.

63.Why do teachers and parents think the book is a good idea?

A.Because it helps with the students’ studies.

B.Because it gives useful information for studying.

C.Because it is used in Shanghai middle schools.

D.Because it teaches students how to be a good person in the online world.

多项选择题