138. Задачка по химии №013 834

98. To determine the mass fraction of the basic substance in technical phenol, a sample of 1.0040 g of it is dissolved in a volumetric flask with a capacity of 500 cm3, brought to the mark with water, and thoroughly mixed. Transfer 10.00 cm3 of the sample into a cone with a ground-in stopper, add 5 cm3 conc. HCl, 50.00 cm3 0.1054 N. bromide bromate mixture, incubated, stirring occasionally for 15 minutes, until the reaction is complete
C6H5OH 3Br2 → C6H2Br3Oh 3 HBr
Then add 2 g of KI, incubate for another 5 minutes and the released iodine is titrated with 40.47 cm3 of 0.1000 n Na2S2O3 solution. Calculate the mass fraction of phenol in a technical product.