CHEM 102
posted by Calvin on .
What is the pH of a solution that is 0.62M H2SO4(aq) and 1.7M HCOOH (formic acid).

This is a VERY complicated problem but here goes.
H2SO4 is a strong acid for the first H that ionizes but a relatively weak acid for the second H. HCOOH is a weak acid.
First, determine the H^+ from H2SO4.
H2SO4 ==> H^+ + HSO4^
HSO4^ ==> H^+ + SO4^2
k2 for HSO4^ is (H^+)(SO4^)/(HSO4^).
Substitute into k2. For H^+ you substitute 0.62+x. For SO4^2 you substitute x and for (HSO4^) you substitute 0.62x. Solve the quadratic for x, then obtain 0.62+x and that will give you the H^+ from the H2SO4. If I didn't make a mistake you should get about 0.08M.
Then HCOOH is a weak acid and it ionizes as
HCOOH ==> H^+ + HCOO^
Set up an ICE chart and look up Ka for HCOOH. The H^+ will be decreased by Le Chatelier's Principle (due to the H^+ from H2SO4). Substitute H^+ from H2SO4 for H^+ an solve for HCOO^. Then add
H^+ from H2SO4 + H^+ from HCOOH to find the total H^+ and divide by liters soln to find M. Convert to pH.