139. Задачка по химии №013 912

15. A sample of bronze weighing 0.4612 g was dissolved in nitric acid and cemented copper and other interfering elements on metallic aluminum. Iron hydroxide was precipitated from the filtrate; the precipitate was dissolved in hydrochloric acid and brought to the mark in a 25.00 ml volumetric flask.
The determination of iron was carried out by microphotometric titration under ultraviolet irradiation. To 5.00 ml of a hydrochloric acid solution of an iron (III) salt, an excess of potassium iodide was added, titrated with 0.02 M Na2S203, and the following data were obtained:
V (Na2S203), ml 0.2 0.4 0.6 0.8 1.0 1.2 1.4
I, μA 1 7 14 21 24 25 25
Build a titration curve and calculate the mass fraction (%) of iron in bronze.

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