posted by tomi .
Calculate [H3O] in the following solutions.
a)4.0×10−2M HCl and 8.0×10−2M HOCl
b)0.105M NaNO2 and 5.00×10−2M HNO2
c)5.15x10-2M HCl and 7.62x10-2M NaC2H3O2
I would do the following:
a) This is a weak acid an a strong acid. I would calculate the Cl^- from HOCl with a common ion of H^+ from HCl, and recognize that (Cl^-) = (H^+) from HOCl. Then determine the H^+ from HCl, and add the two H^+ together.
b)This is a common ion problem or you can use the Henderson-Hasselbalch equation.
c)HCl + NaC2H3O2. It appears there is an excess of H^+ which will react with NaC2H3O2 to form HC2H3O2. That gives you a buffer of C2H3O2 and HC2H3O2 and you use the H-H equation to solve for pH.
Post your work if you get stuck.