First, we need to determine the number of moles of NaOH:
n(NaOH) = m/M = 11.6/40 = 0.29 mole
Then, the concentration of NaOH solution can be calculated:
c(NaOH) = n/V = 0.29/0.129 = 2.25 mol/L
The concentrations of NaOH and OH⁻ ions are equal, so we can determine pOH:
pOH = -log[OH⁻] = -log2.25 = -0.35
Finally, pH value is:
pH + pOH = 14
pH = 14 - (-0.35) = 14.35
