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Redox Example 1 - 6(Fe 2 → Fe 3 1e ± 14 H Cr 2 O 7 2±...

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Lecture Example1: Redox Reaction (Acidic solution) The iron in a 5.675 g sample containing some Fe 2 O 3 is reduced to Fe 2+ . The Fe 2+ is titrated with 12.02 mL of 0.1467 M K 2 Cr 2 O 7 in acid solution. What is the mass of Fe and what is the percentage of Fe in the sample? In almost all cases, the oxygen will have a -2 oxidation state in a compound and the hydrogen will have a +1 oxidation state in a compound. +6 Fe 2+ + Cr 2 O 7 2- Fe 3+ + Cr 3+ Half reactions: Fe 2+ Fe 3+ + 1e - (oxidation, reducing agent) +6 Cr 2 O 7 2- + 6e - 2 Cr 3+ (reduction, oxidizing agent) Balance the oxygen and hydrogen: (One water molecule for every oxygen needed and H + ions to balance the hydrogen on the other side.) Fe 2+ Fe 3+ + 1e - 14 H + + Cr 2 O 7 2- + 6e - 2 Cr 3+
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Unformatted text preview: 6 (Fe 2+ → Fe 3+ + 1e ± ) 14 H + + Cr 2 O 7 2± + 6e ± → 2 Cr 3+ + 7 H 2 O Sum the equations: 6 Fe 2+ → 6 Fe 3+ + 6e ± 14 H + + Cr 2 O 7 2± + 6e ± → 2 Cr 3+ + 7 H 2 O ________________________________________________ 14 H + + Cr 2 O 7 2± + 6 Fe 2+ → 6 Fe 3+ + 2 Cr 3+ + 7 H 2 O From the balanced equation, solve the problem: ( ) % 41 . 10 % 100 675 . 5 5909 . % 5909 . 1 85 . 55 Cr 1 6 Cr Cr 1467 . Cr 01202 . 2 2 2 2 7 2 2 2 7 2 2 7 2 2 7 2 = × = = + + + + + + + + g g sample in Fe Fe g Fe mol Fe g O mol Fe mol O L O mol O L...
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