问题 选择题

在0.10mol•L-1NH3•H2O溶液中,加入少量NH4Cl晶体后,引起的变化是(  )

A.NH3•H2O的电离程度减小

B.NH3•H2O的电离常数增大

C.溶液的导电能力不变

D.溶液的pH增大

答案

A.向氨水中加入氯化铵晶体,铵根离子浓度增大,抑制NH3•H2O电离,则NH3•H2O电离程度减小,故A正确;

B.NH3•H2O的电离常数只受温度的影响,温度不变,则平衡常数不变,故B错误;

C.加入少量NH4Cl晶体后,溶液离子浓度增大,则导电能力增强,故C错误;

D.加入少量NH4Cl晶体后,NH4+离子浓度增大,平衡向逆向移动,c(OH-)变小,pH减小,故D错误.

故选A.

完形填空

.

第二节(共3小题;每小题2分,满分6分)

阅读下面短文,简要回答问题。

The World Health Organization estimates (估计) 20,000,000 babies are born too small each year. It says a baby weighing less than 2,500 grams at birth has a less than desirable weight for good health. 95 percent of such children are born in developing countries.

One recent study shows that pregnant (怀孕的) women in developing countries have healthier babies if the women are given vitamins. Researchers from the United States and Tanzania found that vitamins could help reduce low birth weight. Their findings were reported last month in The New England Journal of Medicine.

Wafaie Fawzi of the Harvard School of Public Health led the study. Professor Fawzi says low birth weight can cause serious health problems in babies. He says low birth weight has been linked to poor growth and mental development, and even early death.

There are fourteen kinds of vitamins. People who do not get enough of these chemicals in their food, or want more, often take multivitamins (多种维生素).In the study, multivitamin pills were given to 4,200 pregnant Tanzanian women.The pills contained all the Bvitamins,as well as vitamins C and E. They also embodied iron and other nutrients in levels several times higher than advised for women in industrial nations.

Four thousand other women received a harmless substance(物质). None of the women had the virus that causes the disease AIDS.

68.On what condition can pregnant women in developing countries have healthier babies?

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69.According to Fawzi, what results will low birth weight lead to?(回答词数不超过10个)

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70.What is the main idea of the passage?(回答词数不超过8个)

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单项选择题