问题 实验题

(9分)小丽同学欲通过实验证明“二氧化锰是过氧化氢分解的催化剂”这一命题。

她设计并完成了下表所示的探究实验:

 实验操作实验现象实验结论或总结
结论总结
实验一取5mL5%的过氧化氢溶液于试管中,伸入带火星的木条有气泡产生,木条不复燃过氧化氢分解产生氧气,但是                   二氧化锰是过氧化氢分解的催化剂
实验二向盛水的试管中加入二氧化锰,伸入带火星的木条没有明显现象                      
实验三                        

                       

                      

          

          

          

二氧化锰能加快过氧化氢的分解,反应文字表达式为:

                      

(1)请你帮小丽同学填写上表中未填完的空格。

(2)在小丽的探究实验中,“实验一”和“实验二”起的作用是        

(3)小英同学认为仅由上述实验还不能完全得出表内的“总结”,她补充设计了两个方面的探究实验,最终完成了对“命题”的实验证明。

第一方面的实验操作中包含了两次称量其目的是:                         

第二方面的实验是利用“实验三”反应后试管内的剩余物继续实验。其目的是      

答案

(1)实验一   反应慢       实验二 二氧化锰加入水中不产生氧气。

实验三 向盛有5mL5%过氧化氢溶液的试管中加入二氧化锰,伸入带火星的木条,

有大量气泡产生,带火星的木条迅速复燃

过氧化氢水+氧气

(2)对比(或对照等);

(3)第一方面:比较MnO2在过氧化氢分解前后的质量。 第二方面:倾倒掉反应后的液体, 向剩余的固体中重新加人过氧化氢溶液,有大量气泡产生,说明MnO2仍然能加快过氧化氢的分解速率(化学性质没变)

题目分析:催化剂是在化学反应中能改变化学反应的速率,而其本身的化学性质和质量都不变的物质。在验证二氧化锰的催化作用时,可设计对比实验,利用对比实验说明二氧化锰能加快反应的速度,且反应前后二氧化锰的质量和化学性质保持不变。二氧化锰只是改变化学反应的速率,所以在设计实验时设计了三个对比实验,一个实验在试管中只放双氧水,双氧水也能分解产生氧气,但产生氧气的速度太慢。第二个实验,即放双氧水,也放二氧化锰,能很快的放出氧气;实验三,向上述试管中加入5mL5%过氧化氢溶液,伸入带火星的木条;有大量气泡产生,火星的木条迅速复燃,剩余物中二氧化锰仍能加快过氧化氢的分解;为了说明二氧化锰在此实验中反应前后的质量保持不变。做了两次称量,目的是比较二氧化锰反应前后质量是否变化。并且在验证二氧化锰的化学性质是否改变时,将剩余的固体中再倒入双氧水,发现双氧水又能很快的放出氧气。

点评:在确定一种物质是催化剂时,不但要确定它能否改变化学反应的速率,还要确定它反应前后的质量和化学性质是否改变。只有这两条都不变,才是催化剂。

阅读理解

阅读理解。

    Quitting smoking can be hard. It is much easier not to start at all.

    One of the reasons that young people smoke is because they think it is cool. Cool people sometimes

smoke a lot in movies, but you may not know that in real life some stars like Jackie Chan think smoking

is bad. Chan doesn't think it is cool at all!

    And sports stars like Yao Ming don't smoke cigarettes, but they are very cool.

    Sometimes people start smoking because their friends ask them to do so, or they see other people like

their parents doing it and think that it's OK. But if other people jumped off a bridge, would you follow them? Of course not,

    Some people think that smoking can stop stress. But there are better ways to beat stress.

    Exercise is one way. Exercise relaxes your muscles. Next time you feel stressed about school, go for a

run!

    Exercise is also a good way to help you quit smoking if you have already started.

    Go for a long walk without money or cigarettes, and breathe in the air around you. Maybe take some

lunch and stop in a park, and think about how much better you feel without a cigarette in your mouth.

    Also think about the money you will save by not smoking. You can spend it on much more fun things

like music, clothes or nice food.

    To stay away from smoking, or to help quit, keep a list with the reasons why smoking is bad.

    If you want to quit, tell your friends so they can help you. If they're good friends, they will

help.

   Millions of people have already quit smoking. It is not difficult if you try hard!

1. Jackie Chan and Yao Ming were mentioned in the article to show ______ .

A. stars never smoke

B. you must stop smoking if you want to become a star

C. you can be cool even if you don't smoke

D. you must smoke to look cool

2. According to the story, which of the following is not a reason why people start smoking?

A. They think smoking is cool.

B. They think smoking can stop them from getting sick.

C. Friends ask them to smoke.

D. They think smoking can help them relax.

3. Which of the following statements is TRUE according to the story?

A. Exercise helps people to relax but can't help quit smoking.

B. Starting smoking because others do so is like following someone to jump off a bridge.

C. Smoking doesn't cost money.

D. It's OK to smoke if your parents do.

4. The underlined word "beat" has the closest meaning to "______ ".

A. hit                          

B. give up

C. do better than                

D. stop       .

5. The best title for this passage is______ .

A. Say No to Smoking

B. Smoking is Cool

C. Non-Smoking Stars

D. How to Help Friends Quit Smoking

单项选择题