Question

Part A= Calculate the [H3O+] of the following polyprotic acid solution: 0.350 M H3PO4.

Part B= Calculate the pH of this solution.

Answer 1

Part A

The acid dissociation goes like (assuming full dissociation) -

Thus , 1 mole of produces 3 moles of

Hence the will be 3 times of  

Hence the

Part B

For calculating pH of weak acid , we need to know it's k_a value .

But this is not provided in the question . So , we have to use the general equation of pH , that is

But this value is getting negative , that is not the correct way . Actually , we are missing the k_a value .Also, pH equation that we used is strictly used for dilute solutions . But for this concentrated solution , we need to use Hammet Acidity Function , but here due to insufficient data , we cannot use that . So , our final answer gives error .