Question

Calculate the pH and the pOH of an aqueous solution that is 0.035 M in HCL (aq) and 0.075 M in HBr(aq) at 25^.C.

Answer 1

HCl H⁺ + Cl^-

1 mole of HCl contains 1 mole of H⁺ so [H⁺] = [HCl] = 0.035 M

HBr H⁺ + Br^-

1 mole of HBr contains 1 mole of H⁺ so [H⁺] = [HBr] = 0.075 M

So the concentration of H⁺ in the mixture is = [H⁺]_{from HCl} + [H⁺] _{from HBr}

                                                               = 0.035+0.075 M

                                                              = 0.11 M

We know that pH = - log [H⁺]

                          = - log 0.11

                          = 0.96

pOH = 14 - pH

       = 14 -0.96

      = 13.04