Question

Calculate the pH during the titration of 20.00 mL of 0.1000 M HBrO(aq) with 0.2000 M NaOH(aq) after 2 mL of the base have been added. K_a of hypobromous acid = 2.3 x 10^-9.

Answer 1

Here, a weak acid HBrO is being titrated with a strong base NaOH.

Volume of weak acid HBrO taken = 20.00 mL = 0.02000 L

Concentration of weak acid taken = 0.1000 M = 0.1000 mol/L

Hence, the number of moles of HBrO present is

The concentration of strong base being added = 0.2000 M = 0.2000 mol/L

Volume of base added = 2 mL = 0.0020 L

Hence, the number of moles of base added is

Now, we can write the reaction between the weak acid and strong base as follows:

Hence, we can create the following ICF table to calculate the concentrations of species present at equilibrium.

Initial, mol	0.00200	0.00040	0	-
Change, mol	-0.00040	-0.00040	+0.00040	-
Equilibrium, mol	0.00160	0	0.00040	-

Hence, at equilibrium we have both the species (weak acid and its conjugate base) present.

Volume of the total mixture = 20.00 mL + 2.00 mL = 22.00 mL = 0.0220 L

Hence, we can calculate the concentrations as follows:

Now, given that the K_a of the weak acid HBrO is

We can calculate the pK_a of the acid which is defined as the negative logarithm of K_a as follows:

Now, we can calculate the pH of the solution by using Henderson-Hasselbalch equation as follows:

Hence, the pH of the solution is approximately 8.036.