# buffer problems - (Feb/03/2006 )

i know i may sound stupid...but im having some problems with these buffer problems. for example:

how would i prepare one liter of .01M acetate buffer, pH 4.53 and calculate the grams of anhydrous sodium acetate (FW 82) and milliliters glacial acetic acid (FW60, density 1.05) needed?

how would i prepare one liter of .1M pyrimidine buffer, pH 5.62 starting with 1.0M pyridine base and disodium citrate (FW 236) if citric acid's pka1 = 3.10, pka2 = 4.75, and pka3 = 5.40?

also, how many grams of solud tris-(hydroxymethyl)-aminomethane (FW 121) and how many milliliters of 1.0N HCl must i use to prepare 500 mL of "tris" buffer, .05M, pH = 7.6 if the pka of tris = 8.4 and crystalline tris exists as: (HOCH2)3CNH3 <-> (HOCH2)3CNH2 + H?

-achung-

QUOTE (achung @ Feb 3 2006, 04:57 PM)
i know i may sound stupid...but im having some problems with these buffer problems. for example:

how would i prepare one liter of .01M acetate buffer, pH 4.53 and calculate the grams of anhydrous sodium acetate (FW 82) and milliliters glacial acetic acid (FW60, density 1.05) needed?

how would i prepare one liter of .1M pyrimidine buffer, pH 5.62 starting with 1.0M pyridine base and disodium citrate (FW 236) if citric acid's pka1 = 3.10, pka2 = 4.75, and pka3 = 5.40?

also, how many grams of solud tris-(hydroxymethyl)-aminomethane (FW 121) and how many milliliters of 1.0N HCl must i use to prepare 500 mL of "tris" buffer, .05M, pH = 7.6 if the pka of tris = 8.4 and crystalline tris exists as: (HOCH2)3CNH3 <-> (HOCH2)3CNH2 + H?

first off a molar solution is moles/litre
formula weight is roughly equivalent to grams per mole

so for q.1-- 1 litre of 0.01M sodium acetate you need 0.01 moles of NaAc for 1 Litre that is the same as formula weight * moles or 82*0.01 which = 0.82g of sodium acetate in one litre...

now as for the glacial acetic acid that (i think) is used to bring the pH to 4.53 for this I am not much help-- I would take to a pH meter and add the acetic acid dropwise until the pH meter reads right...

so that is the same idea for the others-- i think i need more information of buffer composition is your acetate buffer something besides just sodium acetate (I don't understand why the glacial acetic acid here--usually people use HCl for pH adjustments--makes me think that you are making a different thing than I am )

Anyway I guess this isn't much help I think you picked the wrong person to PM as I mentioned I really am not too great at the chemistry stuff... hopefully someone else helps!

-beccaf22-