The pH of a solution can be determined using the formula: pH = -log[H+], where [H+] represents the concentration of hydrogen ions in the solution.
In the case of a 1.25×10-3 M NaOH (sodium hydroxide) solution, NaOH is a strong base that dissociates completely in water to form hydroxide ions (OH-). Since NaOH is a strong base, we can assume that the concentration of hydroxide ions is equal to the concentration of NaOH in the solution.
Therefore, the concentration of hydroxide ions ([OH-]) in the solution is 1.25×10-3 M.
To find the pOH of the solution, we use the formula: pOH = -log[OH-]. Plugging in the value of [OH-], we get:
pOH = -log(1.25×10-3) ≈ 2.90
Since pH + pOH = 14 (at 25 degrees Celsius), we can find the pH by subtracting the pOH from 14:
pH = 14 - 2.90 ≈ 11.10
Therefore, the pH of a 1.25×10-3 M NaOH solution is approximately 11.10.