问题
单项选择题
碘量法测定维生素C注射液时，滴定前应加入
A．甲醇
B．硫酸
C．乙酸乙酯
D．硝酸银
E．丙酮
答案
参考答案：E
解析：维生素C注射液中加有抗氧剂亚硫酸钠，直接滴定会干扰测定，滴定前加入丙酮会和亚硫酸钠发生加成反应，消除干扰。
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碘量法测定维生素C注射液时，滴定前应加入
A．甲醇
B．硫酸
C．乙酸乙酯
D．硝酸银
E．丙酮
参考答案：E
解析：维生素C注射液中加有抗氧剂亚硫酸钠，直接滴定会干扰测定，滴定前加入丙酮会和亚硫酸钠发生加成反应，消除干扰。
The earth is our home and we must take good care of it. That is to say we must 1 the land, air and water clean. But man 2 a lot of pollution on earth since he first made fire, washed his clothes in the river and threw rubbish on the ground. Many years ago, pollution was not so serious 3 there were not so many people. There were enough 4 air, land and water. When the land or the river was dirty in one place, man moved to 5 place. Man is 6 the whole world now. So there is 7 enough clean air, nor clean land, nor clean water now. The more people there are in one place, 8 environment they maybe have. Perhaps you are afraid 9 is endless(无休止的) for people to produce pollution. 10 , we are glad to tell you that people have come to know the danger of pollution. And you can find more and more people are working hard to protect our earth.
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