试题与答案

在18 ℃时,H2SO3的K1=1.5×10-2、K2=5.0×10-7,H2C

题型:选择题

题目:

在18 ℃时,H2SO3的K1=1.5×10-2、K2=5.0×10-7,H2CO3的K1=1.4×10-7、K2=2.7×10-11,则下列说法中正确的是 (  )

A.多元弱酸的酸性主要由第一步电离决定,亚硫酸的酸性弱于碳酸

B.多元弱酸的酸性主要由第二步电离决定,碳酸的酸性弱于亚硫酸

C.多元弱酸的酸性主要由第一步电离决定,亚硫酸的酸性强于碳酸

D.多元弱酸的酸性主要由第二步电离决定,碳酸的酸性强于亚硫酸

答案:

答案:C

题目分析:由二元弱酸H2SO3、H2CO3的电离平衡常数可以看出,多元弱酸溶液的酸性都是主要有第一步电离产生决定。电离平衡常数越大,溶液中的c(H+)就越大,溶液的酸性就越强。由于第一步电离电离平衡常数H2SO3>H2CO3。所以在相同的温度下,亚硫酸的酸性强于碳酸。因此正确选项为C。

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