The amount of iron in a sample can be determined by a titration using dichromate ion, Cr₂O₇^2-, in acidic solution. The iron is first converted to Fe²⁺, which is then titrated by the dichromate ion. The reaction is:
6 Fe²⁺(aq) + Cr₂O₇^2-(aq) + 14 H⁺ $\rarr$ 6 Fe³⁺(aq) + 2 Cr³⁺(aq) + 7 H₂O How many grams of iron are present in a sample if it required 42.7 mL of 0.0180 M Na₂Cr₂O₇(aq) solution for the titration described by the redox equation above?

Question

The amount of iron in a sample can be determined by a titration using dichromate ion, Cr₂O₇^2-, in acidic solution. The iron is first converted to Fe²⁺, which is then titrated by the dichromate ion. The reaction is:
6 Fe²⁺(aq) + Cr₂O₇^2-(aq) + 14 H⁺

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6 Fe³⁺(aq) + 2 Cr³⁺(aq) + 7 H₂O How many grams of iron are present in a sample if it required 42.7 mL of 0.0180 M Na₂Cr₂O₇(aq) solution for the titration described by the redox equation above?

Quizplus · Accepted Answer

First, calculate moles of dichromate: 0.0427 L * 0.0180 mol/L = 0.0007686 mol. From the balanced equation, 1 mol of Cr2O7^2- reacts with 6 mol of Fe^2+. Therefore, moles of Fe^2+ = 0.0007686 mol * 6 = 0.0046116 mol. The molar mass of Fe is 55.85 g/mol, so mass of Fe = 0.0046116 mol * 55.85 g/mol = 0.2576 g, which rounds to 0.258 g.

The Amount of Iron in a Sample Can Be Determined →\rarr→

The Amount of Iron in a Sample Can Be Determined $\rarr$