Monoprotic weak acid in water

[yango_17]

Homework Statement

If enough of a monoprotic acid is dissolved in water to produce a 0.0153 M solution with a pH of 6.31, what is the equilibrium constant, Ka, for the reaction?

Homework Equations

The Attempt at a Solution

I have attempted to solve this problem using ICE tables, but keep getting the incorrect answer. One feedback stated that I needed to account for the initial H+ concentration due to water, which is 10^-7 M, but I'm not sure how to go about putting this into the ICE table. Thanks in advance for any help

 

[Borek]

Please show your work and the result you got, hard to comment on the problem not seeing what you did.

In general concentration of H⁺ from the water autodissociation is not 10^-7 M, as its concentration changes when the acid dissociates shifting the water dissociation equilibrium. This can be still solved, but not with just an ICE table. You would need a full, systematc approach, which requires writing all equations describing the system (Ka, Kw, mass balances, charge balance) and solving for Ka.

 

[epenguin]

Instead of tables which IMHO will leave you with no knowledge or ability a year after the last time you've used them, I would use the simple fundamentals which you will be able to call on any time needed.

What are the relevant equations for this question?