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Topic: Buffer  (Read 3646 times)

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Offline Ak

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Buffer
« on: September 23, 2009, 10:53:33 PM »
Hi all,

so i have this buffer question, where im given histidine with its molecular weight (155g/mol) and starting pH of 7.5 (isoelectric point), and then final volume of 1L, final concentration of 0.1M and final pH of 5.  I have xss 1M HCl and xss 1M NaOH if needed to form the buffer.

My question is, how do i get the 155g/mol into mol/L because i think i need the volume of amino acid stock and then use the henderson-hasselbach equation. or am i going about this the wrong way? Thanks
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Offline Borek

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Re: Buffer
« Reply #1 on: September 24, 2009, 03:03:24 AM »
Do you start with solid histidine or solution?
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Offline Ak

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Re: Buffer
« Reply #2 on: September 24, 2009, 08:33:04 AM »
solid
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Offline Borek

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Re: Buffer
« Reply #3 on: September 24, 2009, 09:18:30 AM »
So you need to know molar mass to be able to prepare solution of known molar concentration.
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Offline Ak

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Re: Buffer
« Reply #4 on: September 24, 2009, 10:05:46 AM »
sorry for my ignorance but im not following

i have the molar mass of 155g/mol...but i dont know how to start
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Offline Borek

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Re: Buffer
« Reply #5 on: September 24, 2009, 10:48:02 AM »
Calculate concentrations from the HH equation.

Honestly, I am not sure how to deal with the question, not having both pKa values (at pH 5 both nitrogens will be protonated). Perhaps you should take them from tables.
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