问题 选择题

用标准盐酸测定NaOH溶液的浓度,甲基橙作指示剂,下列操作可能使测定结果偏低的是(  )

A.酸式滴定管在装酸液前未用标准盐酸溶液润洗2~3次

B.开始实验时酸式滴定管尖嘴部分有气泡,在滴定过程中气泡消失

C.锥形瓶内溶液颜色由黄色变橙色,立即记下滴定管内液面所在刻度

D.盛NaOH溶液的锥形瓶滴定前用NaOH溶液润洗2~3次

答案

答案:C

A中,不润洗,则盐酸的浓度被稀释,所以消耗盐酸的体积偏大,浓度偏高;B中消耗的盐酸体积增加,浓度偏高;C中说明反应还没有达到滴定终点,所以浓度偏低;锥形瓶用氢氧化钠润洗,则消耗盐酸的体积增加,浓度偏高,答案选C。

阅读理解

III.阅读理解(共20小题;每小题1.5分;满分30分)

A

The food we eat seems to have a great effect on our health. Although science has made big steps in making food more fit to eat, it has, at the same time, made many foods unfit to eat. Some research has shown that perhaps eighty percent of human illness is related to food and forty percent of cancer is related to food as well. That food is related to illness is not a new discovery. In 1945, some researchers realized that things commonly used to keep color in meats and other food additives(添加剂)caused cancer.

Yet, these additives remain in our food, and it is difficult to know which things on the wrappings of foods are helpful or harmful. The additives which we eat are not all so direct. Farmers often give penicillin (青霉素) to their animals, and because of this, penicillin has been found in the milk of cows. Sometimes similar tings are supplied to animals not for their health, but just to make a profit.

The farmers are simply trying to fatten the animals in order to get a higher price on the market. Although some countries have tried to control such things, the practice continues.

51. According to this passage, we can know___________.

A. cancer was discovered in 1945

B. science has made food unfit to eat

C. perhaps most of human illness is caused by what we eat

D. perhaps most kinds of cancer are related to what people eat

52. The additives in food_________.

A. are bright and colorless                   B. have indirect effects on our health

C. have direct effects on our health          D. have direct and indirect effects on our health

53. People use additives_________.

A. to change color of the food               B. to make food more unfit to eat

C. to take off the diseases of the food        D. to improve the color and taste of the food

54. Which of the following is Not true?

A. We needn’t take care of what we eat.

B. Some wrappings of food are harmful.

C. “The practice continues” means “things are still going on like that”.

D. Farmers try to make more money on the market by fattening their animals.

单项选择题