11. Consider a solution of formic acid (HCHO2) and sodium formate (NaCHO2), at pH=3.70. After the addition of 0.015 moles of HNO3, the pH decreases by 0.12. What are the initial molarities of HCHO2 and CHO2-, if the Ka of HCHO2 is 1.8x10-4?

Equilibrium system:

HCHO2 (aq) H+ (aq) + CHO2- (aq)

x = [HCHO2], y = [CHO2-], 0.912x = y

Knowing the reaction that occurs, the stoichiometric relationship must be determined:

CHO2- (aq) + H+ (aq) HCHO2 (aq)

CHO2- H+ HCHO2 (aq)
INITIAL
CHANGE
FINAL

What are the initial amounts of each species?

a) 0.015 mol, 0.015 mol, 0.015 mol
b) 0.912x mol, 0.015 mol, x mol
c) 0.912x mol, 0.015 mol, 0.912x mol
d) 0.912y mol, 0.015 mol, y mol