as water is heated , its pH decreases. this means that:
(a)the water is no longer neutral
(b)[H+]>[OH-]
(c)[OH-]>[H+]
(d) two of these are correct
(e)none of these is correct
the value of Ka for 4.00M weak acid HA is____the value of Ka for 8.00Mweak acid HA
(a)greater than
(b)less than
(c)equal to
the pH of a solution at 25度C in which [OH-]=2.1*10^-8 M is
(a)7.7.
(b)6.3.
(c)6.0.
(d)8.0.
(e)none of these
化學3題 求答案 20點
2011-04-18 6:50 am
回答 (2)
2011-04-22 4:15 am
✔ 最佳答案
ㄚ生同學, 第一二題答錯. 1. E
when water heated, pH decreases.
this only implies that [H+] increases; it says nothing about [OH-], whether it increases, decreases or remain unchanged.
what do you mean by "neutral" solution?
usually, when [H=] = [OH-], we say it's neutral.
in fact, [OH-] also increase when water is heated, in extent as same as acid's.
thus, answer should be E.
2. C
Ka is defined as [H+][A-]/[HA] , which is depends on temperature.
Ka should remain unchanged even when concentration changes.
(of course, if you consider that equilibrium constants are defined in terms of activity of substance, not the concentration...)
3. B
Kw = [H+]*[OH-] = 1E-14
[OH-] = 2.1E-8
thus [H+] = 4.76E-7
pH = -log([H+]) = -log(4.76E-7)
= 6.3
2011-04-18 7:39 am
1. b
解析：ph值下降酸性越強
﹝H﹞大於﹝OH﹞
2. a
取 -log 4=-0.6
-log 8=-0.9
-0.6大於-0.9
3.b
-log 2.1*10^8=7.7
POH=7.7
則PH=6.3
解析：ph值下降酸性越強
﹝H﹞大於﹝OH﹞
2. a
取 -log 4=-0.6
-log 8=-0.9
-0.6大於-0.9
3.b
-log 2.1*10^8=7.7
POH=7.7
則PH=6.3
收錄日期: 2021-04-20 00:30:01
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