问题 填空题

根据化学方程式:铅丹+4HNO3=PbO2+2Pb(NO32+2H2O可判断铅丹的化学式为______.

答案

在反应铅丹+4HNO3=PbO2+2Pb(NO32+2H2O中,

由质量守恒定律可知,

反应前后的元素种类和原子的种类、个数相等,

H、N原子的个数前后相等,

反应后共有3个Pb原子,16个O原子,

则反应前应共有3个Pb原子,16个O原子,

反应前已有12个O原子,

则铅丹的构成中应有3个3个Pb原子,4个O原子,

即铅丹的化学式为Pb3O4

故答案为:Pb3O4

阅读理解

阅读理解。

     We asked thirty young people between 14 and 18  several questions. All the children had computers

at home. The average time spent on a computer in a week was about 12 hours, with the highest about 32

hours,  and  the lowest only 5 hours. Most  children  said  they  usually  used  computers  to  play  games.

Fourteen children told  us they did some word-processing(文字处理) at times. Eight people told us they

kept addresses and phone numbers  on  their computers or used them as diaries. Only three people said

they were learning to write computer programs and nobody used databases(数据库). Only two of them

said computers helped with their lessons. The diagram(表格) gives all the results one by one.

     The results  show that computer  use is  quite  common  among 14-18-year-old  children.  They also

show quite clearly that computers are seen  by  most young people as little more than game machines. It

means to us that, though computers are common(普遍) in the homes of young people, they have not yet

become popular in everyday life.

1.In the diagram, what does the letter"c"show?

A.It shows three people between 14 and 18.

B.It shows only 2 of the thirty children.

C.It shows that two of them use computers to help them with their lessons.

D.It shows that three of them use computers to help them write computer programs.

2.Most of the 30 children spent about _______ hours on computers in a week.

A.5

B.12

C.20

D.32

3.There is one mistake in the diagram. What is it?

A.The number of "c" should be lower.

B.The number of "d" should be higher.

C.The number of "a" is too high.

D.There should be no number about "e".

4.In the last paragraph(段)"little more than"means _______.

A.almost the same as

B.far more than

C.different from

D.much more than

5.The writer thinks _______.

A.children must learn to play all kinds of games

B.we should learn many other uses of computers

C.young people should spend more time on computers

D.computers will become much cheaper.

填空题