pH Question?

No. of milli-moles of HCl = (1.5 mmol/mL) × (0.5 mL) = 0.75 mmol
Volume of the final solution = (0.5 + 0.5) mL = 1.0 mL
Concentration of HCl of the resulting solution = (0.75 mmol) / (1.0 mL) = 0.75 M

1 mole of HCl dissociates to give 1 mole of H⁺ ions.
Hence, [H⁺] of the resulting solution = 0.75 M
pH of the resulting solution = -log[H⁺] = -log(0.75) = 0.12
pOH of the resulting solution = 14.00 - pH = 14.00 - 0.12 = 13.88