November 29, 2021, 04:44:52 AM
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Topic: buffer preparation calculation  (Read 139 times)

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Offline mana

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buffer preparation calculation
« on: November 27, 2021, 02:52:30 PM »
Hi all
in buffer calculation, as you know we have to use Henderson Haselbach equation to find the concentration ratio of salt to acid, now my question is then how I can find how much acid and salt must be added, I have found a solved problem but I'm not sure is the last step (calculation of the weight of salt and acid) is right or not, I would be grateful tell me is it right and if so, how does it work.
thanks in advance for your help
« Last Edit: November 27, 2021, 03:07:03 PM by mana »

Offline Borek

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Re: buffer preparation calculation
« Reply #1 on: November 27, 2021, 03:23:34 PM »
0.4 M buffer (if I read it right) means sum of concentrations of the acid and its conjugate base is 0.4 M. That gives you an additional equation. Solution as shown does something equivalent (uses molar fractions), but doesn't explain where they come from (I haven't checked numbers, but the general logic of the approach seems OK: for a given A/B molar ratio molar fraction of A is A/(A+B)).

Not your fault, but pH 6 is way too far from acetic acid pKa for a serious buffer.
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Offline mana

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Re: buffer preparation calculation
« Reply #2 on: November 27, 2021, 03:33:49 PM »
0.4 M buffer (if I read it right) means sum of concentrations of the acid and its conjugate base is 0.4 M. That gives you an additional equation. Solution as shown does something equivalent (uses molar fractions), but doesn't explain where they come from (I haven't checked numbers, but the general logic of the approach seems OK: for a given A/B molar ratio molar fraction of A is A/(A+B)).

Not your fault, but pH 6 is way too far from acetic acid pKa for a serious buffer.
thank you very much  :)

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