Question

How many grams of sodium acetate are required to prepare buffer solution of pH = 4 using 1 L of N/10 acetic acid. How will the pH be affected when 1.5 L H₂O is added to this buffer solution (Given K_a = 2.0 x 10^-5).

Answer 1

A mixture of acetic acid and sodium acetate is an acidic buffer Using Henderson equation

[Salt] = 2 x 10^-2 M = 0.02

It is difficult to take anti log of negative number, rather than above equation we may use the same relation in the form.

mass of salt = 0.02 x 82 = 1.64 g

The addition of water (1.5 L) decreases the concentration of both acid and salt, the ratio log₁₀ [salt] / [acid] remains constant, Hence, the pH is unaltered.