问题 选择题

已知:Na2O+H2O═2NaOH,向饱和的氢氧化钠溶液中加入一定量的Na2O,充分反应后恢复到原来温度.下列说法中,正确的是(  )

A.溶液中溶质质量增多,溶液的质量减少

B.溶液中溶质质量增多,溶液的质量增加

C.溶液中水的质量减少,溶质质量分数不变

D.溶液中水的质量减少,溶质质量分数增大

答案

根据反应Na2O+H2O═2NaOH知,向饱和的氢氧化钠溶液中加入一定量的Na2O,由于反应消耗了水,溶液中的溶剂质量减少,由于生成了氢氧化钠,溶质的质量可能增加,由于原氢氧化钠溶液是饱和的,溶剂又减少了,加入Na2O充分反应后恢复到原来温度,溶液仍饱和,且会出现剩余固体不能溶解.

A、原氢氧化钠溶液是饱和的,反应消耗了水,生成了氢氧化钠,生成的氢氧化钠不能溶解,溶液中溶质不会增加,反而会减少,由于溶液中的溶质和溶剂都减少了,溶液的质量也减少,前错后对,所以错误.

B、原氢氧化钠溶液是饱和的,反应消耗了水,生成了氢氧化钠,生成的氢氧化钠不能溶解,溶液中溶质不会增加,反而会减少,由于溶液中的溶质和溶剂都减少了,溶液的质量也减少,前后都错,所以错误.

C、原氢氧化钠溶液是饱和的,反应消耗了水,生成了氢氧化钠,反应后恢复到原来温度,溶液仍饱和,且会析出剩余固体,但同一温度下的饱和溶液中溶质的质量分数是定值,所以正确.

D、原氢氧化钠溶液是饱和的,反应消耗了水,生成了氢氧化钠,反应后恢复到原来温度,溶液仍饱和,且会析出剩余固体,但同一温度下的饱和溶液中溶质的质量分数是定值,前对后错,所以错误.

故选C.

阅读理解

“I sometimes get up at three or four in the morning and I surf the net.”

“I often check my e-mail forty times a day.”

“I often spend more than three hours during one time on the net.”

“I spend more time in chat rooms than with my ‘real-1ife’ friends.”

Do you know any people like these? They are part of a new addiction(瘾) called Internet addiction. Internet addicts spend at least thirty to forty hours online every week. The use of the Internet can be an addiction like drug(毒品) use. People lose control of the time they spend on the Internet

For example, one college student was missing for several days. His friends were worried, and they called the police. The police found the student in the computer lab: he was surfing the net for several days straight.

Studies show that about 6 to 10% of Internet users become addicted. And people worry about the teens because the Internet is changing the playing field for some of them. They spend more time in cyberspace than in the real world of friends and family.

Is ‘surfing the net’ a hobby or an addiction for you? You may have a problem if you have these symptoms(症状):

●You do not go to important family activities or you do not do school work because you like to spend hours on the Internet.

●You can’t wait for your next online time.

●You plan to spend a short time online, but then you spend several hours.

●You go out with your friends less and less.

小题1:What does the beginning of the passage tell us?

A.How to become an Internet addict.

B.What an Internet addict usually does.

C.Where to find an Internet addict.

D.Why to write this passage.小题2:How does the writer describe the addicts’ use of Internet?

A.It is something like keeping drugs.

B.It is a way of producing drugs.

C.It is like taking drugs.

D.It is terrible to imagine.小题3:Why do people worry about the teens?

A.The teens are wasting too much money.

B.They used to work on the Internet.

C.The playing field of the teens will disappear.

D.More and more of the teens wil1 become addicted to the Internet.小题4:The example in the passage shows that _______.

A.Internet problems are more serious among college students

B.Internet addicts usually stay in the computer lab without sleep

C.Some of the Internet users have already been seriously addicted

D.The police often help to find those Internet addicts.小题5:What is the writer trying to tell us at the end of the passage?

A.Don’t be addicted to the Internet.

B.Go to family activities more often.

C.Do things as you have planned.

D.Stay with your parents as often as possible.

选择题