A chemist titrates 100.0mL of a 0.3444M hydrocyanic acid HCN solution with 0.8414M KOH solution at 25°C . Calculate the pH at equivalence. The pKa of hydrocyanic acid is 9.21 . Round your answer to 2 decimal places.

Answer : The pH at equivalence is, 11.30

Explanation : Given,

Concentration of = 0.3444 M

Volume of = 100.0 mL = 0.1 L    (1 L = 1000 mL)

First we have to calculate the moles of

As we known that at equivalent point, the moles of HCN and KOH are equal.

So, Moles of KOH = Moles of HCN = 0.03444 mol

Now we have to calculate the volume of KOH.

Total volume of solution = 0.1 L + 0.0409 L = 0.1409 L

Now we have to calculate the concentration of KCN.

The balanced equilibrium reaction will be:

Moles of KCN = 0.03444 mol

At equivalent point,

Given:

Now put all the given values in the above expression, we get:

Therefore, the pH at equivalence is, 11.30