50. Solving a chemistry problem

110. When determining lead in zinc ore by the addition method, a sample of ore weighing m (g) was dissolved in a mixture of acids, Fe (III) was reduced, gelatin was added and diluted to 200.0 ml. An aliquot of the solution with a volume of 20.0 ml was placed in an electrolyzer and the height h1 of the polarographic wave was measured at E = –0.45 V (n.e.c.e). Under these conditions, ions of copper, zinc, cadmium, iron (II) do not interfere with the determination of lead. After adding a standard 0.0020 M solution with a volume of Vst Pb(NO3)2 to the electrolyzer, the height h2 was obtained. Calculate the mass fraction of lead in the ore using the following data:
task number 110
m, g 3.0700
h1, mm 28.4
Vst, ml 2.00
h2, mm 32.4