Question

Buffers STAT! You are working in a high-powered clinical biochemistry lab. The chief scientist rushes in and announces, "I need 500 ml if .2 M acetate, pH 5.0. STAT!" You have sold anhydrous sodium acetate (MW = 82 g/mol) and a solution of 1M acetic acid. Describe how you would make the buffer.

Answer 1

From Handerson equation, pH of buffer solution is given by

pH = Pka + log[salt]/[acid]

Given that, pH = 5.0

pKa of acetic acid = 4.74

[sodium acetate] = 0.2 M

[Acetic acid] = 1.0 M

To get a 500mL of pH of 5.0 buffer solution using 0.2M CH3COONa and 1M CH3COOH, it is required to take in the following ratio

pH = 4.74+log(0.2*450/1*50) = 5.0

It is required to make a 0.2 M of 450 mL sodium acetate solution

The weight of sodium acetate required to make 0.2M of 450 mL solution is given by

M = (wt/mol.wt)(1000/V(mL))

0.2 = (wt./82)(1000/450) = 7.38 g