A 200 ml sample of a citrus fruit drinks containing ascorbic acid (vitamin C) was acidified with H₂SO₄ and 10 ml of 0.025 M-I₂ was added. Some of the I₂ was reduced by the ascorbic acid to I⁻. The exc

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A 200 ml sample of a citrus fruit drinks containing ascorbic acid (vitamin C) was acidified with H₂SO₄ and 10 ml of 0.025 M-I₂ was added. Some of the I₂ was reduced by the ascorbic acid to I⁻. The excess of I₂ required 2.5 ml of 0.01 M-Na₂S₂O₃ for reduction. What was the vitamin C content of the drink in microgram vitamin per ml drink? C₆H₈O₆ + I₂ → C₆H₆O₆ + 2HI; 5H₂O + S₂O₃²⁻ + 4I₂ → 2SO₄²⁻ + 8I⁻ + 10H⁺

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I₂ added = 10×0.025 = 0.25 mmol. Thiosulphate used = 2.5×0.01 = 0.025 mmol; with the given 1:4 stoichiometry, excess I₂ = 4×0.025 = 0.1 mmol. I₂ consumed by ascorbic acid = 0.25-0.1 = 0.15 mmol = mmol of vitamin C (1:1). Mass = 0.15×176 = 26.4 mg in 200 ml = 26400/200 = 132\ \mug/ml. Ans 0132.

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