Question

A buffer solution is prepared by mixing 0.01 М HCN and 0.02 M sodium cyanide. If pK_a for HCN is 5.20, what is the pH of solution?

Options

• 4.4

• 5.5

• 6.5

• 3.2

Answer 1

5.5

Explanation:

For an acidic buffer solution.

`pH = pK_a + log_10  "[Salt]"/"[Acid]"`

`pH = 2.50 + log_10  0.02/0.01`

`pH = 5.20 + log_10 2`

= 5.20 + 0.3010

= 5.501