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Chemistry- pka and pH calculations

Could you help me with this question? I'm not too sure how to go about it
For an experiment you need to prepare 329 mL of a Phosphate buffer with a total phosphate concentration of 569 mM. The pH of this buffer should be 7.6. The relevant acid has a pKa = 7.2. You have the following substances:
Na2HPO4 with a molecular mass of 142 g/mol,
KH2PO4 with a molecular mass of 136 g/mol
How much of each compound do you have to weigh in for this buffer?
Acid g ?
and
Base g ?
Original post by coffee alert
For an experiment you need to prepare 329 mL of a Phosphate buffer with a total phosphate concentration of 569 mM. The pH of this buffer should be 7.6. The relevant acid has a pKa = 7.2. You have the following substances:
Na2HPO4 with a molecular mass of 142 g/mol,
KH2PO4 with a molecular mass of 136 g/mol
How much of each compound do you have to weigh in for this buffer?
Acid g ?
and
Base g ?


What are your ideas?

ka = [H+][A-]/[HA]
This is me jotting my notes down

so pH=pKa

same amount of acid and base



so pH=pKa-log(Acid/Base)

log(Acid/Base)=pKa-pH

=7.2-7.6=-0.4



log(Acid/Base)= -0.4

so I have to raise that by the power of ten but im not too sure what value

so I did 10^-0.4???= 0.3981071706



so ratio would be 2 to 4 acid and base

but then from there im not too sure since i think

NA2HPO4 acid= 142g/mol=7.882 mol??? im not too sure where im going with this
this question is the last question and so ive been struggling with it- since i will score only 0% which is why I'm panicking
its due tuesday morning, which doesn't help
wait i think the answers are
18.97g base
7.265g acid

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