Calculate the number of grams of ammonium chloride that must be added to 2.00 l of a 0.500 m ammonia solution to obtain a buffer of ph = 9.20. assume the volume of the solution does not change as the solid is added. kb for ammonia is 1.80×10−5.

Amount of NH4Cl that must be added = 61.5 g

Explanation:

Given:

Concentration of ammonia, [NH3] = 0.500 M

Volume of solution = 2.00 L

pH of buffer = 9.20

Kb (NH3) = 1.80*10^-5

To determine:

The amount of NH4Cl to be added

Explanation:

NH3/NH4Cl is a basic buffer, the corresponding Henderson-Hasselbalch equation is:

where kb = base dissociation constant

BH+ = conjugate acid = NH4Cl

B = base = NH3

It is given that pH = 9.20, therefore,

Substituting the appropriate values into the Henderson equation gives:

[NH4Cl] = 0.574 M

the answer to this question is 3.