Phosphate Buffer Concentration Calculation

[hianghao]

Homework Statement

To prepare 1M phosphate buffer pH7.8. pKa=7.21. How much molar of Na2HPO4 and NaH2PO4 to be added
I have no confidence in my answer... Can anyone pls have a check?

Homework Equations

pH=pKa+lg (base/conjugate acid)

The Attempt at a Solution

7.8=7.21 +lg (a/b)
0.59=lg (a/b)
a/b=3.89
a+b=1-----1
a=1-b -----2
(1-b)/b=3.89
b=0.2045 -Na2HPO4
a=0.7955 -NaH2PO4

Is my way of doing it correct? Did i forget to calculate other things that i must?

 

[Borek]

Your approach is correct. But:

a/b=3.89
a+b=1-----1

OK

(1-b)/b=1

Check your math.

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[hianghao]

Your approach is correct. But:



OK



Check your math.

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buffer calculator, concentration calculator
pH calculator, stoichiometry calculator

I see...Thanks for the correction :D