Question

You are given sodium acetate, 1M HCl, NaHCO3 and Na2CO3. Determine which of these four you would need and then show calculations to make buffer pH = 4.7 by method 2. Assume making 100 mls of a 0.1 M buffer.

Answer 1

We require Sodium acetate & Na2CO3.Bcoz, buffer is a solution of weak acid & salt of that weak acid with strong base. Sodium acetate is salt of weak acid acetic acid.

Calculations :

Concentration of salt = x

Concentration of salt = (0.1 - x )

pH = pKa + log [Salt] / [Acid]

4.7 = - Ka + log [ 0.1 - x ] / [ x ]

4.7 = (10 - 1.75*10^-5) + log [0.1 - x ] / [ x ]

4.7 = 5.25 + log [ 0.1 - x ] / [ x ]

log [ 0.1 - x ] / [ x ] = - 0.55

[ 0.1 - x ] / [ x ] =0.0744