问题 问答题

为测定某氯水的物质的量浓度,取100mL氯水,加入足量的碘化钾溶液充分反应,然后用300ml 1mol/L硫代硫酸钠(Na2S2O3)溶液恰好完全吸收生成的碘单质,问100mL氯水中溶解了多少L标准状况下氯气?(已知:2Na2S2O3+I2=Na2S4O6+2NaI)

答案

由题意可知,发生的反应有Cl2+2KI═2KCl+I2、2Na2S2O3+I2=Na2S4O6+2NaI,

且碘化钾溶液足量,硫代硫酸钠溶液恰好完全吸收生成的碘单质,

则存在Cl2~2Na2S2O3,n(Na2S2O3)=0.3L×1mol/L=0.3mol,

则n(Cl2)=

0.3mol
2
=0.15mol,

标况下Vm=22.4L/mol,

则100mL氯水中溶解的标准状况下氯气的体积为0.15mol×22.4L/mol=3.36L,

答:100mL氯水中溶解了3.36L标准状况下氯气.

阅读理解

阅读理解。

                                                A good choice

     Harry's father buys a magazine called Choice. It gives its readers

information about all kinds of products-cameras, radios, computers, cars,

etc .This information helps them make the best choice when they buy

something.

     Harry borrowed his father's magazine when he nee-ded a new computer.

" I'II read about  all the different computers , " he said, " and choose the best

one. "

     The magazine described these three computers.

     The  DGT PC450 : This computer comes with lots of good software.

However,it does not have much memory and is rather slow. At  $2,850, it's

not very good value for money.

     The BNK 975XF : At $3 ,200 , this is the most expensive computer we

tested. However,it is also by far the most reliable. It is very fast and has lots

of memory. It is worth the extra money if you can afford it.

     The CGP 8PT: At only  $1,900, this is the cheapest computer we tested. It has plenty of memory and is quite fast. However,it "crashed" twice while we were testing it and we cannot recommend it for reliability.

     Harry chose the BNK 975XF. "I know it's expensive,Dad, "  he said, " but it will last me a long time and do everything I want it to do. " 

1. What is the main idea of this passage?

A. Harry likes to read computer magazines.

B. Harry borrowed his dad's magazine to help him choose a computer.

C. Harry chose the most expensive computer.

D. Harry chose the most reliable computer.

2. Which computers have lots of memory?

A. The DGT PC450 and the BNK 975XF.

B. The BNK 975XF and the CGP 8PT.

C. The CGP 8PT and the DGT PC450.

D. All the computers.

3. Why doesn't Choice recommend the CGP 8PT for relia-bility ?

A. Because it isn't very fast.

B. Because it doesn't come with any software

C. Because it crashes too often.

D. Because it's cheap.

单项选择题