Answer to Question #7958 in Chemistry for Oluwatobi Ajetomobi

Question

Sodium Fluoride is used in many types of toothpaste to give them basic pH. Sodium ions do not affect the pH of the solution. Prove that fluoride ions shift pH into basic range by finding pH of the 0.023mol/l solution of sodium fluoride.

Answer 1

When NaF hydrolyzes it will form HF and NaOH; since HF is a weak acid, and NaOH is a
strong base, the resulting solution will be basic. The dissociation constant for
HF is 1.58*10^-4 so most of the F^- ions will remain in HF molecules. Each "lost"
H⁺ ion increases the OH^- ion concentration by the same amount by "removing" an H
atom from H₂O and releasing an OH^- ion

[OH^-] = [NaF]

pOH = -log(0.023] = 1.64

pH = 14.0 - pOH = 12.4