How to get Kb ?

Asoom · May 26, 2009, 01:02 AM

The PH of 0.1M MCl (M^+ is an unknown cation ) was found to be 4.7. Write the ionic equation for the hydrolysis of M^+ and its corresponding equilibrium expression Kb . Calculate the value of Kb

Perito · May 26, 2009, 05:02 AM

The pH of 0.1M MCl (M^+ is an unknown cation ) was found to be 4.7. Write the ionic equation for the hydrolysis of M^+ and its corresponding equilibrium expression Kb . Calculate the value of Kb

Hydrolysis of M+:

$M^+ + H_2O \rightleftharpoons MOH + H^+$ (Equation 1). The pH is 4.7, so we're in acid solution.

$Kb = \frac {[MOH][H^+]}{[M^+]}$ (Equation 2)

where [] indicates concentration.

$pH = 4.7 = -log([H^+])$ (Equation 3)

Can you take it from here? You'll have to figure out [MOH] and [M^+] to calculate Kb.