[Ak]

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

[Borek]

Do you start with solid histidine or solution?

[Ak]

solid

[Borek]

So you need to know molar mass to be able to prepare solution of known molar concentration.

[Ak]

sorry for my ignorance but im not following

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

[Borek]

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.