(a) Using the expression 𝐾𝑎=[H+][A−][HA], explain how to determine which solution has the lower pH, 0.10𝑀HF(𝑎𝑞) or 0.10𝑀HC2H3O2(𝑎𝑞). Do not perform any numerical calculations.

To determine which solution has a lower pH, we need to look at the Ka values of the two solutions. The Ka value is a measure of the strength of an acid in solution. The higher the Ka value, the stronger the acid and the lower the pH.

The expression Ka = [H+][A-]/[HA] gives us the acid dissociation constant. In this expression, [H+] is the concentration of hydrogen ions, [A-] is the concentration of the base (the conjugate base of the acid), and [HA] is the concentration of the undissociated acid.

For a 0.10M HF(aq) solution and a 0.10M HC2H3O2(aq) solution, the concentration of the undissociated acid [HA] is the same. Therefore, the solution with the higher [H+] (and thus the higher Ka) will have the lower pH.

HF and HC2H3O2 are both weak acids, but HF is a stronger acid than HC2H3O2. This means that HF will have a higher Ka value than HC2H3O2. Therefore, a 0.10M HF(aq) solution will have a lower pH than a 0.10M HC2H3O2(aq) solution.