# science(chem)

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The pKa of HEPES is 7.55 at 20C and it's MW is 238.31. Calculate the amounts of HEPES in grams and of 1.0M NaOH in ml that would be needed to make 300ml of 0.2M HEPES buffer at 7.2.

I'm not sure how to go about doing this problem.

• science(chem) -

http://www.science.smith.edu/departments/Biochem/Biochem_353/Buffer_Prep.html#top

There is a better site but I can't find it now. Its done by Haverford College (UK).

• science(chem) -

I'll see how I do with that site, first.
Thanks Dr.Bob

• science(chem) -

I found the other site. Here it is.
http://www.haverford.edu/chem/Scarrow/GenChem/acidbase/buffer_prep.html

The usual biochemistry buffers means one thing and analytical chemists express buffers another way (or I may be out of touch with the new day thinking). At any rate, a 0.1 M buffer in the biochemistry sense means that base + acid = 0.1; i.e., 0.1 is the total of the species in whatever form they appear, such as acid and conjugate base. My experience in analytical chemistry is for 0.1 M acetic acid buffer to mean 0.1 M in acetic acid and we calculate how much acetate to add to make it the desired pH(or how much NaOH to add to make the acetate). You will need to decide which of these interpretations to use when solving the problem.

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