Exercise 10 | Oxidation-Reduction Reactions

The amount of Fe2+ (aq) in an FeSO4 (aq) solution can be determined by titration with a solution containing a known concentration of Ce4+ (aq).

Calculate the molarity of Fe2+ (aq) and the mass of iron in the sample if 42.5 mL of 0.100 M Ce4+ (aq) is required to completely oxidize 30.0 mL of Fe2+ (aq) to Fe3+ (aq).

Reaction: Fe2+ (aq) + Ce4+ (aq) → Fe3+ (aq) + Ce3+ (aq)


At the equivalence: nFe2+ = nCe4+

⇒ [Fe2+] x VFe2+ = [Ce4+] x VCe4+

⇒ [Fe2+] = [Ce4+] x VCe4+VFe2+

⇒ [Fe2+] = 0.100 x 42.530.0 = 0.142 M

 

mFe = mFe2+ = nFe2+ x MFe

⇒ mFe2+ = [Ce4+] x VCe4+ x MFe

⇒ mFe2+ = 0.100 x 42.5 x 10-3 x 55.845

⇒ mFe2+ = 0.237 g