30. Solving a chemistry problem

1. For the nephelometric determination of zinc, to construct a calibration graph, 18.0 was introduced into 50 ml volumetric flasks; 14.0; 10.0; 6.0; and 2.0 ml (V, ml) of a standard zinc salt solution containing 5 mg/ml zinc. Suspensions of K2Zn3[Fe(CN)6] 2 were prepared in these solutions and their apparent optical densities (D) were measured:
V, ml 18.0 14.0 10.0 6.0 2.0

D 0.18 0.22 0.33 0.54 0.9

The analyzed solution with a volume of 25.0 ml was placed in a volumetric flask with a capacity of 50.0 ml and a suspension of K2Zn3[Fe(CN)6]2 was prepared in it. The apparent optical density (DX) of this solution was equal to:
Option 1
DX 0.42


Determine the zinc content in the analyzed solution in g/l.