1. What mass of methylamonium chloride would be added to 250.0 mL of 0.20 M solution of methylamine to produce a solution with a pH of 10.0?

2. What mass of methylamonium chloride would be added to 250.0 mL of 0.20 M solution of methylamine to produce a solution with a pH of 11.3?

3. Comment on the difference between the mass of methylamonium chloride added in parts a and b.

Answer

14.9 g of methylamonium chloride must be combined with 250.0 mL of 0.20 M methylamine to produce a solution with pH of 10.0.

0.74 g of methylamonium chloride must be combined with 250.0 mL of 0.20 M methylamine to produce a solution with pH of 11.3.

The pH of a buffer solution with equal amount of methylamine and methylamonium ion is 10.6 (see previous problem). To make a more acidic buffer (pH = 10.0), more acid must be added. To make a more basic buffer (pH = 11.3) less acid must be added.

Explanation

1. Need to find the inital concentration of methylamonium ion in the equilibrium calcalations.
2. The mechanics of both parts of the problem are identical; the numbers differ.