Using activities calculate the pH of a solution containing 0

Using activities, calculate the pH of a solution containing 0.013 M NaOH plus 0.0120 M LiNO₃.

Solution

As defined pH is -log [Hydrogen ion concentration]. For alkali it will be 14 -log[OH ion concentration]) . This relationship is true for dilute solutions only. You have 0.013 M NaOH and 0.012 M LiNO3. LiNO3 is a salt and is supposed to be neutral. Therefore pH of the mixture will mainly depend upon NaOH.
Here pH = 14 (-log[0.013])
= 14 - (-[-2.1139])
= 14 - (1.886)
= 12.114
pH will be 12.1