问题 问答题

小军根据燃烧红磷测定空气中氧气含量的实验原理,认为可用木条燃烧产生的木炭代替红磷测定空气中氧气的含量,并按如图装置进行实验.(集气瓶底铺有细沙)

(1)小军检查装置气密性后,将盛有足量红热木炭的燃烧匙迅速伸入集气瓶中,并把塞子塞紧,木炭在瓶内燃烧的文字表达式______ 待红热的木炭熄灭并冷却至室温后,打开弹簧夹,并未发现倒吸现象.经过认真分析,小军从实验操作上找到失败的原因是______.

(2)小军将集气瓶中的细沙改为一种无色液体重复上述实验,有倒吸现象,他可能用到的无色液体为______.

答案

(1)木炭在氧气中燃烧生成二氧化碳,文字表达式为:碳+氧气

点燃
二氧化碳;

(2)实验室测氧气含量的反应原理:通过可燃物消耗氧气使装置内压强减小,外界液体就可以等体积进入,从而测定出氧气的体积;由于木炭燃烧后生成等体积的氧气,因此导致装置内的压强没有变化,故不会有倒吸现象的发生;

(3)要想测定出氧气的体积分数,可以选择氢氧化钠溶液,二氧化碳和氢氧化钠反应生成碳酸钠和水,集气瓶中压强减小,有倒吸现象.

故答案为:(1)碳+氧气

点燃
二氧化碳;

(2)集气瓶中的压强没有变化;

(3)氢氧化钠溶液.

阅读理解

IV. 阅读理解(共15小题;每小题2分,满分30分)

阅读下列短文,从每题所给的四个选项(A、B、C和D)中,选出最佳选项,并在答题卡上将该项涂黑。

A

The private automobile(私家车) has long played an important role in the United States. In fact, it has become a necessary and important part of the American way of life. In 1986, sixty-nine percent of American families owned at least one car, and thirty-eight percent had more than one. By giving workers rapid transportation, the automobile has freed them from having to live near their place of work. This has encouraged the growth of the cities, but it has also led to traffic problems.

For farm families the automobile is very helpful. It has made it possible for them to travel to town very often for business and for pleasure, and also to transport their children to distant schools.

Family life has been affected in various ways. The car helps to keep families together when it is used for picnics, outings, and other shared experiences. However, when teenage children have the use of the car, their parents can’t keep an eye on them. There is a great danger if the driver has been drinking alcohol or taking drugs—or is “showing off ” by speeding or breaking other traffic laws. Mothers of victims(受害者) of such accidents have formed an organization called MADD (Mothers Against Drunk Driving). These women want to prevent further tragedies(悲剧). They have worked to encourage the government to limit the youngest drinking age. Students have formed a similar organization, SADD(Students Against Drunk Driving) and are  spreading the same message among their friends.

For many Americans the automobile is a necessity. But for some, it is also a mark of social position and for young people, a sign of becoming an adult. Altogether, cars mean very much to Americans.

56.Which of the following is NOT mentioned in the text?

A. Cars have encouraged the growth of the cities.

B. Cars can bring families together when they go for picnics.

C. Cars have enabled people to live far from their place of work.

D. Cars help city families to transport their children to faraway schools.

57.What has been done to deal with the problem of drunk driving?

A. Parents have paid more attention to their children.

B. Some organizations have been set up against drunk driving.

C. Mothers have tried to persuade their children not to drink alcohol.

D. University students have asked the government to solve the problem.

58.We can infer from the text that __________ in America.

A. it will be more difficult for people to get new cars.

B. parents will not allow their children to have their own cars.

C. the government will encourage people to use public transportation.

D. cars will still be popular though they have caused many problems.

单项选择题