22. To determine iron by high-frequency titration, the test solution was placed in a 50 ml volumetric flask and brought to the mark with water. An aliquot of 5 ml of the resulting solution was transferred to a cell and titrated with 0.009897 M Na2H2EDTA solution. We received the following data:
V (EDTA) ml 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0
Readings 55.0 51.0 49.5 44.5 42.2 40.0 37.5 35.0 33.0 30.2
Device

V (EDTA) ml 11.0 11.5 12.0 12.5 13.0 13.5 14.0 15.0
Readings 28.0 26.3 25.7 26.5 27.5 30.0 31.0 33.0
Device

Construct a titration curve and calculate the mass of iron in the test solution in milligrams.

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