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Alcohol level in blood can be determined by a redox titration with dichromate solution in acidic medium according to the balanced equation C 2 H 5 OH aq + 2 Cr 2 O 7 2 - aq + 1 6 H + ⟶ 2 CO 2 g + 4 Cr 3 + aq + 1 1 H 2 O l ⁡ What is blood alcohol level in mass percent if 8.0 mL of 0.05 M Cr 2 O 7 2 - solution is required for titration of a 10.0 g sample of blood?

Options

  1. A0.092%
  2. B0.01%
  3. C1.4%
  4. D1.2%

Correct answer

A. 0.092%

Step-by-step solution

C 2 H 6 O → 2 CO 2 + 4 + 12e - (n Factor = 12) Cr 2 O 7 2 - + 1 4 H + + 6 e - → 2 Cr 3 + + 7 H 2 O (n Factor = 6) Cr 2 O 7 2 - = 8 × 0.05 × 6 1 0 0 0 = 0.0024 Eqs = Eqs of C 2 H 5 OH Moles of ethanol = 0.0024 1 2 = 0.0002 moles = 2 × 1 0 - 4 × 4 6 = 9 2 × 1 0 - 4 g % Ethanol = 9 2 × 1 0 - 4 1 0 × 1 0 0 = 0.092 %

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