Question

Ammonia, NH₃, is a weak base with a Kb value of 1.8 x 10⁻⁵.

What is the pH of a 0.450 M ammonia solution?
Express your answer numerically to two decimal places.

Answer 1

To find the pH of a 0.450 M ammonia solution, use the Kb value of ammonia to set up an equilibrium expression, solve for hydroxide ion concentration, calculate pOH, and then determine pH as pH + pOH = 14.

Step-by-step explanation:

To calculate the pH of a 0.450 M ammonia solution, we first need to use the Kb value for ammonia, which is 1.8 x 10⁻⁵. The ammonia (NH3) partially ionizes in water to form hydroxide ions (OH⁻) and ammonium ions (NH4+).

Using the expression for the base ionization constant (Kb), we can set up an equilibrium expression where Kb = [NH4+][OH⁻]/[NH3].

Since ammonia is a weak base, we can assume that the concentration of hydroxide ions formed is equal to x and that the change in concentration of NH3 is negligible.

Therefore, Kb = x²/[NH3] where [NH3] is approximately 0.450 M. By solving for x, we find the concentration of hydroxide ions.

Then, we can calculate pOH by taking the negative logarithm of the hydroxide ion concentration, and finally pH since pH + pOH = 14.