Question

What is the pH of .0003 M of NaOH

Answer 1

We are given that the concentration of NaOH is 0.0003 M and are asked to calculate the pH

We know that NaOH dissociates by the following reaction:

NaOH → Na⁺ + OH⁻

Which means that one mole of NaOH produces one mole of OH⁻ ion, which is what we care about since the pH is affected only by the concentration of H⁺ and OH⁻ ions

Now that we know that one mole of NaOH produces one mole of OH⁻, 0.0003M NaOH will produce 0.0003M OH⁻

Concentration of OH⁻ (also written as [OH⁻]) = 3 * 10⁻⁴

pOH of the solution:

pOH = -log[OH⁻] = -log(3 * 10⁻⁴)

pOH = -0.477 + 4

pOH = 3.523

pH of the solution:

We know that the sum of pH and pOH of a solution is 14

pH + pOH = 14

pH + 3.523 = 14                              [subtracting 3.523 from both sides]

pH = 10.477