问题 选择题

在一个化学反应中,如果有元素化合价升高,同时就有元素化合价降低。已知钾与水反应生成对应的碱和一种气体,该气体可能是(   )

A.H2

B.O2

C.CO2

D.NH3

答案

答案:A

分析:根据题意可知“化学反应中,如果有元素化合价升高,同时就有元素化合价降低”,结合这句话从化合价的升高和降低、碱的组成及元素守恒定律来分析即可.

解答:解:首先根据化学反应前后元素守恒定律可知,反应前没有碳元素和氮元素参与反应,所以生成物中不可能出现CO2和NH4的物质.所以选项C、D错误.

其次根据生成物有碱,可知碱一定是KOH,

根据“化学反应中,如果有元素化合价升高,同时就有元素化合价降低”可知,另一种气体不是氧气,因为反应前后钾元素的化合价从0价升高到+1价,反应前水中O元素的化合价为-2价,反应后若生成O2,化合价升高,不符合题中所给信息.而生成氢气,氢元素化合价有+1价变为0价,化合价降低,符合题中要求.

故选A

点评:解答本题要熟悉常见元素和原子团的化合价及摄取信息并加以运用.

阅读理解

When you do not use your arms or your legs for some time, they will become weak. When you start using them again, they slowly become strong again. Everybody knows that. Yet many people do not seem to know that memory (记忆 )  works in the same way.

When someone says that he has a good memory, he really means that he keeps his memory in practice by using it.  When someone else says that his memory is poor, he really means that he does not give it enough chance to become strong.

If a friend says that his arms and legs are weak, we know that it is his own fault (过错).  But if he tells us that he has a poor memory, many of us think that his parents may be blamed (责备 ) , and few of us know that it is just his own fault. Have you ever found that some people can’t read or write but usually they have better memories? This is because they cannot read or write but they have to remember things, they cannot write them down in a small notebook.  They have to remember days, names, songs and stories, so their memory is being exercised the whole time.

So if you want to have a good memory, learn from the people: practice remembering things in a way as other people do.

小题1: Someone can’t have a good memory if _     

A.his parents don't have a good memory

B.he can't read or write

C.he doesn’t use his memory

D.he doesn't use his arms or legs for some time小题2: If you do not use your arms or legs for some time,                    _

A.they become weak and wont become strong until you use them again

B.they will become stronger

C.they become weak but they slowly become strong again

D.you cant use them any more小题3: Which of the following is true?

A.Your memory works in the different way as your arms or legs.

B.Your memory, like your arms or legs, becomes weak if you do not give it enough chance

to practice.

C. Don't learn how to read or write if you want to have a better memory.

D.A good memory comes from less practice.小题4: Few people know that it is only _     if a friend has a poor memory.

A.his grandmother's fault

B.his parents fault

C.his teachers’ fault

D.his own fault小题5: The writer wants to tell us________ .

A.how to have a good memory

B.how to read and write

C.how to use our arms or legs

D.how to learn from the people

名词解释