[eutopia]

"Quantitively, describe how to prepare 250 mL of a 0.10 M solution of a buffer with a pH = pKa.

i did:
molecular weight of buffer (sodium carbonate monohydrate) = 124.01g, so i need 3.10025 g to make it 0.10M
given HCl = .1047M
conjugate acid = NaHCO3 (mw = 84.01)

but i dont know where to go from there

[AWK]

in this way you can do two buffers based on Ka2 or Ka1 (this one will work badly).

[eutopia]

oh i forgot to mention:

pKa1 = 9.8
pKa2 = 6.2

i dont understand what people mean when they say that since pH=pKa according to hendersonhasselbalch [A-] = [HA], so I was assuming that 0.1 M of HCl is needed... but some people tried to tell me that 1/2 of HCl --> 0.05 M is needed to make pH = pKa?

[GCT]

oh i forgot to mention:

pKa1 = 9.8
pKa2 = 6.2

i dont understand what people mean when they say that since pH=pKa according to hendersonhasselbalch [A-] = [HA], so I was assuming that 0.1 M of HCl is needed... but some people tried to tell me that 1/2 of HCl --> 0.05 M is needed to make pH = pKa?

you're not being very clear about the problem, are you simply adding two solutions (acid and its conjugate base) or are you adding the acid/base and then adding enough base/acid to obtain the buffer; it seems that the problem pertains to the latter situation.  In that case, here are some things to consider

the initial pH of the acid or basic solution

how much acid would you need to add to the acid or base to have an equal concentration of acid and base?

[AWK]

Write down a balanced equation stepwise.
From them you can find that your case may be 1/4 or 3/4 of needed HCL for completing reaction.