Answer to Question #127359 in General Chemistry for A.J

Question

Calculate the pH of a solution of 0.25 M RbBrO2. Ka HBrO2 = 1.2 x 10-5

Answer 1

Answer on Question #127359, Chemistry, General Chemistry

Calculate the pH of a solution of 0.25 M RbBrO₂. Ka _HBrO2 = 1.2 x 10^-5

Solution:

RbBrO₂ is a salt which consists of cation of the strong base RbOH and anion of the weak acid HBrO₂. Hydrolysis reaction is:

RbBrO₂ + H₂O = RbOH + HBrO₂ - molecular equation

BrO₂^- + H₂O = OH^- + HBrO₂ - ionic equation (pH > 7, basic medium)

The pH value of this salt can be calculate as:

pH = 7 + (рКа - рС)/2, where:

pKa = - lg Ka = - lg (1.2 x 10^-5) = 4.92

pC = - lg C(RbBrO₂) = - lg 0.25 = 0.60

So:

pH = 7 + (4.92 - 0.60)/2 = 9.16

Answer: pH = 9.16.