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Topic: how to figure out the concentration??  (Read 9291 times)

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Offline DanChen2014

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Re: how to figure out the concentration??
« Reply #15 on: March 12, 2014, 11:51:20 AM »
In this case, you have to consider the weak acid effect.

C6H8O6 + H2O ::equil:: C6H7O6- + H3O+     pKa= 4.1

X2/(0.05×50×10-3-X)=10-4.1

X=4.08×10-4 M

[C6H8O6 ]=(0.05×50×10-3)-4.08×10-4=2.09×10-3 M
« Last Edit: March 12, 2014, 12:07:01 PM by DanChen2014 »
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Offline Borek

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Re: how to figure out the concentration??
« Reply #16 on: March 12, 2014, 01:27:56 PM »
You are contradicting yourself. If you want to that nitpicky you should not treat the initial solution as 50 mM, as acid in it is dissociated too.
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Offline DanChen2014

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Re: how to figure out the concentration??
« Reply #17 on: March 12, 2014, 09:47:53 PM »
Quote from: Borek on March 12, 2014, 01:27:56 PM
You are contradicting yourself. If you want to that nitpicky you should not treat the initial solution as 50 mM, as acid in it is dissociated too.

Just because in this case, the effect can not be ignored. 50mM was given, I assumed that was the real concentration.

Anyway, I will not post this kind of answer any more. Sorry for anything I have done which may not follow the forum's rule.
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