Question

Potassium dichromate is used to titrate a sample containing an unknown percentage of iron. The sample is dissolved in H₃PO₄/H₂SO₄ mixture to reduce all of the iron to Fe₂+ ions. The solution is then titrated with 0.01625 M K₂Cr₂O₇ (orange), producing Fe₃+ and Cr₃+ (colorless) ions in acidic solution. The titration requires 32.26 mL of K₂Cr₂O₇ for 1.2765 g of the sample. Provide a sketch of the titration before and after the analysis. Use the mass percentage to determine if the original sample is iron (II) iodate, iron (II) phosphate, or iron (II) acetate?

Answer 1

Potassium dichromate is used as a titrant to determine the percentage of iron in a sample. The iron is first reduced to Fe²+ ions and then titrated with K₂Cr₂O₇. The mass percentage of iron in different compounds can be calculated to identify the original sample.

Step-by-step explanation:

Potassium dichromate is used as a titrant to determine the percentage of iron in a sample. The iron in the sample is first reduced to Fe²+ ions by dissolving it in a mixture of H₃PO₄/H₂SO₄. Then, the solution is titrated with a known concentration of K₂Cr₂O₇. The titration reaction involves the oxidation of Fe²+ to Fe³+ and the reduction of Cr₂O₇²- to Cr³+ ions. The balanced reaction is:

6Fe²+ (aq) + 14H+ (aq) + Cr₂O₇²- (aq) → 6Fe³+ (aq) + 2Cr³+ (aq) + 7H₂O(1)

The titration requires 32.26 mL of 0.01625 M K₂Cr₂O₇ to react with 1.2765 g of the sample. To determine the original sample composition, the mass percentage of iron in each possible compound (iron (II) iodate, iron (II) phosphate, iron (II) acetate) needs to be calculated and compared to the experimental value obtained from the titration.