What volume in milliliters of 0250 M NaOH should be added to

What volume (in milliliters) of 0.250 M NaOH should be added to a 0.135 L solution of 0.0170 M glycine hydrochloride (pKa1 = 2.350, pKa2 = 9.778) to adjust the pH to 2.70?

Solution

GH + NaOH <----------> G-Na + H2O

pH = pKa + log [G-Na]/[GH] ,

2.70 = 2.35 + log [G-Na]/[G-H]

[G-Na]/[G-H] = 2.2387

[G-Na] = 2.2387 [G-H]

G-Na moles = 2.2387 G-H moles

0.250 x V = 2.2387 (0.135 x0.0170 - 0.250 V)

0.250 V = 2.2387 (0.002295 - 0.250 V)

0.250 V = 5.1378 x 10^-3 - 0.5597 V

V = 6.346 x 10^-3 L

volume of NaOH = 6.35 mL