Concept explainers
Vitamin C, ascorbic acid (C6HgO6)(molar mass 176.1 g/mol), is a reducing agent. One way to determine the ascorbic acid content of a sample is to mix the acid with an excess of iodine,
C6HgO6(aq) + I2(aq) + H2O(l) → C6HgO6(aq) + 2 H3O+(aq) + 2 I–(aq)
and then titrate the iodine that did not react with the ascorbic acid with sodium thiosulfate. The balanced, net ionic equation for the reaction occurring in this titration is
I2(aq) + 2 S2O32–(aq)→2 I–(aq) + S4O62–(aq)
Suppose 50.00 mL of 0.0520 M I2 was added to the sample containing ascorbic acid. After the ascorbic acid/I2, reaction was complete, the I2 not used in this reaction required 20.30 mL of 0.196 M Na2S2O3 for titration to the equivalence point. Calculate the mass of ascorbic acid in the unknown sample.
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Chapter 4 Solutions
Chemistry & Chemical Reactivity
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