Question

Buffers can also be basic. Would a solution that is 0.2M in ammonia and 0.2M in ammonium chloride be a buffer?Explain. Could you make a brief drawing showing the composition of this solution. Write the henderson-hasselbach equation for a basic buffer and calculate the pH.

Answer 1

Given data:

Concentration of ammonia, i.e. [NH₃] = 0.2 M and that of ammonium chloride, i.e. [NH₄Cl] = 0.2 M

Given combination: NH₃ / NH₄Cl , i.e. a mixture of weak base and its salt with the strong conjugate acid.

Here, the concentrations of both NH₃ and NH₄Cl = 0.2 M, a condition of half equivalence point. It can be drawn as

2NH₃ + HCl NH₃ + NH₄Cl

Henderson-hasselbalch equation can be written as

pH(basic buffer) = pKb(NH₃) + Log{[NH4Cl]//[NH3]}

= 4.7 + Log(0.2/0.2)

= 4.7 + Log(1)

= 4.7 + 0

= 4.7

i.e. pH = pKb. Hence, the combination NH₃ (0.2 M)/ NH₄Cl (0.2 M) is a good buffer.