Fireworks contain KClO₃. To analyze a sample for the amount of KClO₃ a chemist first reacts the sample with excess iron(II),

and then titrates the resulting solution with Ce⁴⁺ [in the form of (NH₄)₂Ce(NO₃)₆]

to determine the quantity of iron(II) that did not react with ClO³⁻. (This is referred to as a “back titration.”) Suppose a 0.1342-g sample of a firework was treated with 50.00 mL of 0.0960 M Fe²⁺. The unreacted Fe²⁺ ions then required 12.99 mL of 0.08362 M Ce⁴⁺. What is the weight percent of KClO₃ in the original sample?

Transcribed Image Text:

ClO3(aq) + 6 Fe2+ (aq) + 6 H3O+ (aq) - Cl(aq) + 9 H₂O(l) + 6 Fe³+ (aq)