The pH of a solution that has two monoprotic weak acids such as acetic acid and benzoic acid can be calculated using the following equation:

Where, Ca1 and Ca2 are the concentrations in Molarity for the two acids, and Ka1 and Ka2 are the respective acid ionization constants for the two acids.

For example, assuming a solution with 0.01 M acteic acid (Ka=1.76E-5) and 0.001 M benzoic acid (Ka=6.30E-5) then by applying the above equations we get pH = 3.31.

Keeping in mind that the above equation is correct given that Ca1 and Ca2 are much greater than Ka1 and Ka2, and greater than the hydronium ion concentration.

A free online pH calculator can be used to find solution for such pH problems.

Where, Ca1 and Ca2 are the concentrations in Molarity for the two acids, and Ka1 and Ka2 are the respective acid ionization constants for the two acids.

For example, assuming a solution with 0.01 M acteic acid (Ka=1.76E-5) and 0.001 M benzoic acid (Ka=6.30E-5) then by applying the above equations we get pH = 3.31.

Keeping in mind that the above equation is correct given that Ca1 and Ca2 are much greater than Ka1 and Ka2, and greater than the hydronium ion concentration.

A free online pH calculator can be used to find solution for such pH problems.

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