You are making a 1L solution that you want to be buffered with ammonia and ammonium. However ammonia is a gas that is difficult to dissolve directly in water with good precision. Instead you will start with ammonium chloride and add sodium hydroxide which will react with the ammonium to form ammonia. Which of the following combinations will give you the optimal buffered solution?

a. 54 grams ammonium chloride and 108 grams sodium hydroxide

b. 54 grams ammonium chloride and 54 grams sodium hydroxide

c. 54 grams ammonium chloride and 40 grams sodium hydroxide

d. 54 grams ammonium chloride and 10 grams sodium hydroxide

54 grams ammonium chloride and 40 grams sodium hydroxide

Explanation:

A buffer is a solution that contains either a weak acid and its salt or a weak base and its salt, the solution is resistant to changes in pH. This means that, a buffer is an aqueous solution of either a weak acid and its conjugate base or a weak base and its conjugate acid.

A Buffer is used to maintain a stable pH in a solution, buffers can neutralize small quantities of additional acid of base. For any buffer solution, there is always a working pH range and a set amount of acid or base that can be neutralized before the pH will change. The amount of acid or base that can be added to a buffer before changing its pH is called its buffer capacity.

A good buffer mixture is supposed to have about equal concentrations of its both components. It is a rule of thumb therefore, that a buffer solution has generally lost its usefulness when one component of the buffer pair is less than about 10% of the other component.

The implication of this is that the ammonium chloride and sodium hydroxide should be of approximately the same concentration. If the masses are dissolved as shown in the answer, then we will have 1molL-1 of each component of the buffer in accordance with the rule of thumb stated above.