Question

To find the pH of a solution of NH4Br directly, one would need to use:__________

Select the correct answer below:
a) the Kb of NH3 to find the hydroxide concentration
b) the Ka of NH+4 to find the hydronium concentration
c) the Kb of NH3 to find the hydronium concentration
d) the Ka of NH+4 to find the hydroxide concentration

Answer 1

b) the Ka of NH₄⁺ to find the hydronium concentration

Step-by-step explanation:

The equilbrium of NH₄⁺ (The conjugate acid of NH₃, a weak base), is:

NH₄⁺ ⇄ NH₃ + H⁺

Where Ka of the conjugate acid is:

Ka = [NH₃] [H⁺] / [NH₄⁺]

Thus, if you know Ka of NH₄⁺ and its molar concentration you can calculate [H⁺], the hydronium concentration, to find pH (Because pH = -log [H⁺])

Thus, right option is:

b) the Ka of NH₄⁺ to find the hydronium concentration