15. Solving a chemistry problem

6. Nickel chloride is extracted from an aqueous solution of 100 ml in the form of dimethylglyoximate with 10 ml of chloroform and diluted with chloroform to 25 ml. From the resulting solution, aliquots of 5 ml are photometrically added by the method of additions. Calculate the unknown content of nickel in the solution, taking into account its incomplete extraction, if it is known that the optical densities of chloroform extracts with and without the addition of 20 μg of nickel are 0.45 and 0.20, respectively. The distribution coefficient of nickel dimethylglyoximate in the chloroform-water system is 410. Answer: 82.1 µg.