(a)

Step 1:

The amount of HCN is 50 ml = 0.05 l.

Molarity of the HCN is 0.2 M.

Equilibrium constant for HCN is .

Calculate pH when 0.0 mL of KOH has been added.

HCN is at equilibrium.

The formula for equilibrium constant .

At equilibrium .

pH definition:

It is the measure of the acidity and alkalinity of a solution.

pH is the negative log of the activity of the hydrogen ion.

(b)

Step 1:

The amount of HCN is 50 ml = 0.05 l.

Molarity of the HCN is 0.2 M.

The amount of KOH added is 25 ml.

Molarity of KOH is 0.2 M.

Equilibrium constant for HCN is .

Calculate pH when 25 mL of KOH has been added.

Moles of = Molarity * Volume

Moles of = 0.2 * 0.05

Moles of = 0.01

Moles of = 0.2 * 0.025

Moles of = 0.005

moles acid in excess = .

Total volume = 0.05 + 0.025 = 0.075

pH definition:

It is the measure of the acidity and alkalinity of a solution.

pH is the negative log of the activity of the hydrogen ion.