Question

A solution is made by dissolving 8.2 g of NaOH in approximately 450 mL of water in a volumetric flask. The solution becomes quite warm, but after it is allowed to return to room temperature, water is added to total 500 mL of solution. Calculate the pH of the final solution. Report pH to 2 decimal places.

Answer 1

13.61

Step-by-step explanation:

First, we will calculate the molar concentration of NaOH in the final solution.

M = mass NaOH / molar mass NaOH × liters of solution

M = 8.2 g / 40.00 g/mol × 0.500 L

M = 0.41 M

NaOH is a strong base that dissociates according to the following balanced equation.

NaOH → Na⁺ + OH⁻

Then, the concentration of OH⁻ is also 0.41 M.

The pOH is:

pOH = -log [OH⁻]

pOH = -log 0.41 = 0.39

The pH is:

pH + pOH = 14

pH = 14 - pOH = 14 - 0.39 = 13.61