95. In synthetic acetic acid in the form of an impurity there can be up to 0.4% formic acid, determined iodometrically according to the following scheme:
3НCOONa + 2 KМnO4 → K2CO3 + NaCO3 + NaHCO3 + MnO2 + H2O
MnO2 + 2KI + 2H2SO4 → MnSO4 + K2SO4 + I2 + 2 H2O
The released iodine is titrated with a Na2S2O3 solution in the presence of starch. For analysis, take 50.00 cm3 of 99% acetic acid (p = 1.055), distill 50.00 cm3 of 0.1000 n KMnO4 solution, keep the mixture in a dark place for 30 minutes. Then 0.5 g of KI 50 cm3 H2SO4 1: 1 is introduced. The titration of the released iodine consumed 22.85 cm3, 0.1020 M Na2S2O3 solution. Conclude whether the sample meets the acetic acid specification.
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