What volume in milliliters of 0230 M NaOH should be added to

What volume (in milliliters) of 0.230 M NaOH should be added to a 0.135 L solution of 0.0220 M glycine hydrochloride (pKa1 = 2.350, pKa2 = 9.778) to adjust the pH to 2.60?

Solution

Since the pKa2 is very less than pka1,

assuming that the [H+] is dependent only on pka1 value

Using the hessley henderbach equation

pH = pKa + log[A-/HA]

2.60 = 2.350 + log[A-/HA]

log[A-/HA] = 0.25

Reaction will be

NaOH + HA ----- NaA + H2O

Number of moles of HA = 0.0220 * 0.135L

= 0.00297 moles

Number of moles of NaOH = 0.00297 * 0.25/4.715

= 0.0001574 moles

V/1000 * 0.230 = 0.0001574

V = 0.6843 L

=684.3 mL