Michael's Week 3 worksheet

[Melody Shadanloo 2J]

Hi! Does anyone know how to solve this problem?

The pKb of the conjugate base of chlorous acid is 12.08. A 0.15 M
solution of chlorous acid was made to use as an inorganic acid in the synthesis of a new
pharmaceutical. What is the pOH of this solution at equilibrium?

I keep getting 7.5482, but the answer is 12.57 instead. Thank you!

[harshita_ravi_2E]

Hi! Here's what I did:

The reaction is HClO + H2O --> H3O + ClO-

Since the reaction produces hydronium ions, we need to find the Ka. Since we've been given the pKb, we need to convert this to Ka.
pKa = 14-12.08 = 1.92
Ka = 10^-1.92 = 0.012022

When you set up the ICE table, the equation you get is (x^2)/(0.15 -x) = 0.012022. When you rewrite this as a quadratic, you get x^2 + 0.012022x - 0.00180.

Using the quadratic equation to solve (we take the positive value), we get x = 0.0368. This gives us the concentration of hydronium ions, so we can take the -log(0.0368) to find the pH. This is 1.433. To find the pOH, subtract 14-1.433 = 12.56. Hope this helped :)