问题 选择题

在甲、乙、丙、丁四个烧杯中分别加入2.3gNa、6.2gNa2O、7.8gNa2O2和4.0g NaOH,而后各加入100mL水,搅拌,使固体完全溶解,则甲、乙、丙、丁溶液中物质的量浓度大小顺序正确的是(    )

A.甲=丁<乙<丙

B.丁<甲<乙=丙

C.丁<乙=丙<甲

D.丁<甲<乙>丙

答案

答案:B

甲2.3g Na与水反应生成氢氧化钠和氢气,所以溶液中溶质是氢氧化钠;根据化学式Na→NaOH知,生成氢氧化钠的质量为4g,溶液的质量=钠和水的质量-氢气的质量=2.3g+100g-0.1g=102.2g,所以该溶液的质量分数×100%=3.9%;

乙6.2g Na2O与水反应生成氢氧化钠,溶液中的溶质是氢氧化钠;根据化学式Na2O→2NaOH知,生成氢氧化钠的质量为8g,溶液的质量=氧化钠和水的质量=6.2g+100g=106.2g,所以该溶液的质量分数为×100%=7.5%;

丙7.8g Na2O2与水反应生成氢氧化钠和氧气,所以溶液中的溶质是氢氧化钠;根据化学式Na2O2→2NaOH知,生成氢氧化钠的质量为8g,溶液的质量=过氧化钠+水的质量-氧气的质量=7.8g+100g-1.6g=106.2g,所以该溶液的质量分数为×100%=7.5%;

丁4.0g NaOH溶于水和水不反应,所以溶液的溶质为氢氧化钠,溶液的质量=氢氧化钠的质量+水的质量=4.g+100g=104g,所以溶液的质量分数为 ×100%=3.8%.

所以溶液的质量分数正确的是丁<甲<乙=丙,故选B.

单项选择题
阅读理解

How to improve our life? Many people think that they have to accept whatever life throws at them. They’ll say, "This is my destiny(命运).I cannot change it."

Of course not! You don’t have to suffer needlessly. Your life depends on you, not on any other external(外部的)factor.

I know a woman who says she just accepts what life gives her because she has done everything she can to improve it. Guess what her lifestyle is? She wakes up in the morning, goes to work, comes back home, relaxes, chats with people, watches TV, and then goes to sleep. Next day, the same routine cycle follows.

Huh! Is this what she calls "doing her best"? She believes she has tried her best and just accepts it in her heart that this is the life that has been intended for her and that her luck can only change if God wills it. She hasn’t realized that we have to do our share of making the effort to live the life of our dreams.

Remember that you harvest what you sow. You have to get off the sofa, get your eyes off the TV screen, get your hands off the phone(unless it contributes to your success),and get your mind and body to work! Don’t expect your luck to change, unless you do something about it. If something goes wrong, don’t just regard it as a temporary setback; instead, learn your lesson, make the most of the situation, and do something to solve the problem. It’s not enough to think positively; you also have to act positively.

If someone’s life is in trouble, do you just hope and pray that things will turn out fine? Of course not! You get to do anything you can to save the person. So it is with your own life. It is not enough to hope for the best, but you have to do your best. In other words, don’t just stand(or sit)there, do something to improve your life.

小题1:According to the woman mentioned in Para. 3, her life_________________.

A.doesn’t need improving

B.couldn’t be improved

C.will be better some day

D.will be worse in the future小题2: What does the author think of the woman’s life?

A.Positive

B.Passive

C.Colorful

D.Disturbing小题3:Which of the following statements is the author’s opinion?

A.Your temporary problem is not discouraging.

B.Your luck can be changed by your own efforts.

C.You can only achieve success when God wills it.

D.You should treat yourself in the way you treat friends.小题4:In Para. 5, the author emphasized the importance of _______________.

A.positive thinking

B.positive action

C.hope for the best

D.intention to succeed小题5: The text is mainly written to advise you to _________________.

A.understand yourself

B.improve your life

C.believe in yourself

D.change your normal way