- #1

jibjab

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## Homework Statement

Prepare 750 mL of 0.5 M phosphate buffer, pH 6.7 and pKa 7.21. NaH2PO4 (119.96 g/mol) and Na2HPO4 (141.96 g/mol) is available to use.

## Homework Equations

pH=pKa+log(B/A)

## The Attempt at a Solution

I have the solution from my teacher, but I have no idea how he got the numbers. Could someone please explain how to use this equation? I'm trying to work backwards (I'm terrible at math, I learn the methods from solved examples) but I can't figure out where the numbers are coming from:

6.7=7.21 +log(B/A)

B=0.3090A (How did he get that?)

0.75L x 0.5 mol/L = 0.375 mol = B+A

1.3090A = 0.375 (Why is it 1.3090 and not 0.3090A like above?)

34.37g = 119.96 x (He put a symbol here that looks like <=) A=0.2865 mol

12.57g = 141.96 x <= B=0.885 mol

If someone would explain the process above, I would be extremely grateful. Thanks