94. Solving a chemistry problem

40. From the analyzed solution with a volume of 50 ml containing the sulfosalicylate complex of iron (III) with a maximum in the absorption spectrum at λ = 416 nm (pH = 9-11.5), a sample was taken and its optical density was measured A (X) = 0.350 in cell with an absorbing layer thickness l = 1 cm at A = 416 nm.
We prepared five reference solutions containing iron(III) sulfosalicylate complex (рН = 9-11.5) with precisely known concentration c(Fe3) of iron(III), measured their optical density A in the same cuvette at the same wavelength and obtained following results:
C(Fe3 ), mg/l 0.001 0.002 0.003 0.004 0.005
A 0.093 0.186 0.279 0.372 0.465
Build a calibration graph in the coordinates A - c (Fe3), mol / l. Determine the coefficient of proportionality to in the equation c (Fe3), mol / l \u003d k * A. Find the concentration c(Fe3 ), mol/l and mass m(Fe3*), mg of iron(III) in the analyzed solution.
Answer: k \u003d 1.72 * 10-4; c(Fe3)=6.02 10-5 mol/l; m(Fe3)=0.188 mg.