Determine the percent ionization of a 0.215 m solution of benzoic acid.

Explanation:

The percent ionization of a weak acid is the percent of the original acid that ionizes.

You may calculate the percent ionization of an acid of known concentration, from the equilibrium constant.

So, to determine the percent ionization of a 0.215 M solution of benzoic acid, you must look for the equilibrium (dissociation or ionization) constant.

Equilibrium constants depend on temperature. So, you must know the temperature.

For this question, I will assume 25°C, for which you can find that the dissociation constant, Ka, for benzoic acid is 6.25×10⁻⁵.

With that, you follow these steps:

1. Write the ionization equation:

2. Calculate the concentration of the ion C₆H₅CO₂⁻ at equilibrium

                    C₆H₅CO₂H ⇄ C₆H₅CO₂⁻ + H⁺

       I           0.215                  0              0

      C            - x                   + x           + x

      E          0.215 - x              x              x

        Ka = x² / 0.215 - x =  6.25×10⁻⁵

           x² = 0.215 × 6.25×10⁻⁵ = 0.0000078125

           x = 0.00367 M

           If you do not make the assumption but solve the quadratic equation you will get x = 0.00363 M

3. Calculate the percent ionization:

With x = 0.00363 M (exact calculation)

With x = 0.00367 M

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)