Solving for Ka of unknown weak acid 

The weak acid*

@@TheSamaiya09 Hi, that's something that would need to be given in the problem.

Very nice explanation

Thanks for the question. If you just have molarity and pH: 1. Solve for [H3O+] using pH 2. Set up Ka expression 3. Solve for "E" in ICE table (it will be molarity-x for the equilibrium concentration of the weak acid, x is the [H3O+]) 4. Plug equilibrium values into Ka. Hope that helps!