Question

Calculate the pH of the solution of 0.112M CsBrO. I know Cs+ and Br- are spectator ions but I can't figure out how to solve this.

No volume was given nor is it necessary to solve a weak acid/base problem when it is not a mixture. The final pH is 10.82 I just need the steps to solve it.   

Answer 1

HBrO , Ka = 2.8 x 10^-9

Kb = Kw / Ka

Kb = 1.0 x 10^-14 / 2.8 x 10^-9

Kb = 3.57 x 10^-6

CsBrO -----------------> Cs+ + BrO-

Cs+ is the only spectator ion . BrO - ion will particiapte in hydrolysis because it came from weak acid

BrO- + H2O ------------------> HBrO + OH-

0.112 0 0 -------------> initial

-x + x + x ------------> change

0.112-x x x ------------------> equilibrium

Kb = [HBrO][OH-]/[BrO-]

3.57 x 10^-6 = x^2 / 0.112-x

x^2 + 3.57 x 10^-6 x - 4.0 x 10^-7 = 0

by solving this

x = 6.32x 10^-4

x = [OH-] = 6.32 x 10^-4 M

pOH = -log [OH-]

pOH = -log (6.32 x 10^-4)

pOH = 3.20

pH + pOH = 14

pH + 3.20 = 14

pH = 10.8 --------------------------> answer