Question

A buffer was prepared by mixing 46.60g ammonia (NH3; Kb= 1.79 x 10-5) and 63.80g ammonium chloride (NH4Cl) in 500.00 ml of solution. Calculate the pH of the buffer.

Answer 1

K_b of ammonia is given to be .

Hence, K_a of the conjugate acid ammonium ion can be calculated as

Hence, pK_a of the acid can be calculated as

Amount of NH₃ = 46.60 g

Molar mass of ammonia = 17.031 g/mol

Hence, the number of moles of ammonia taken is

Total volume of the solution is 500.00 mL = 0.500 L

Hence, concentration of NH₃ is

Amount of NH₄Cl taken = 63.80 g

Molar mass of NH₄Cl = 53.491 g/mol

Hence, number of moles of NH₄Cl is

Hence, concentration of NH₄Cl is

Now, we can use the Henderson-Hasselbalch equation to calculate the pH of the buffer as follows:

Hence, the pH of the buffer is about 9.61.