Question

A buffer solution is prepared by mixing 0.1 M ammonia solution and 0.25 M solution of NH₄CI. What is the value of pK_b to maintain its pOH at 6?

Options

• 5.60

• 6.40

• 1.50

• 6.63

Answer 1

5.60

Explanation:

For a basic buffer solution,

pОН = pКb + log₁₀ `= ["Salt"]/["Base"]`

`6 = pK_b + log_10  0.25/0.1`

`pK_b = 6 - log_10  5/2`

= 6 – [log₁₀ 5 – log₁₀ 2]

= 6 – [0.699 – 0.301]

= 5.602