A0.500 m solution of a weak base has a ph of 9.75. what is the base hydrolysis constant, kb, for the weak base?

The hydrolysis constant for the hydrolysis reaction of the weak base is the

equilibrium constant for the reaction.

The hydrolysis constant is approximately 1.581 × 10⁻⁶

Reasons:

The concentration of the weak base solution = 0.500 m

The pH of the weak base = 9.75

Required:

The hydrolysis constant for the base

Solution:

Equation for the reaction is BOH B⁺(aq) + OH⁻(aq)

pH = 9.75

∴ [H⁺] ≈ 1.778 × 10⁻¹⁰

The pOH = 14 - 9.75 = 4.25

pOH = -log[OH⁻]

Therefore;

4.25 =  -log₁₀[OH⁻]

[OH⁻] = = 5.623 × 10⁻⁵ moles

Number of moles of BOH that dissociates in the solution is therefore;

OH⁻ = B⁺ = 5.623 × 10⁻⁵ moles

The number of moles of BOH left in the solution is given as follows;

BOH = (0.5 m - 5.623 × 10⁻⁵ )

The hydrolysis constant, , is given as follows;

The hydrolysis constant, ≈ 1.581 × 10⁻⁶

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