I have to solve an exercise that I've been trying for a long time without success.
Information that I have:
- pH @ certain temperature of an aqueous dissolution of an acid
- molar concentration of the acid
Unknown:
- approximate $\mathrm{p}K_\mathrm{a}$ (is not meant to be calculated with calculator I suppose that is the reason they say "approximate")
So far I tried to express the chemical equation and its two steps to finally get $\ce{H3O+}$ and an oxid. I've calculated backwards the Hydronium concentration $[\ce{H3O+}]$ with the $\mathrm{pH}$ formula. $$ \mathrm{pH} = -\log([\ce{H3O+}])$$. I've written down the formula to calculate $K_\mathrm{a}$ from where I expected to be able to calculate $\mathrm{p}K_\mathrm{a}$.
I don't know how to extract now the concentrations of every component on the $K_\mathrm{a}$ formula in order to be able to calculate that. Moreover, what am I suppose to do with the temperature?
I hope you can give me guidance in the process to solve such exercises.