15. Solving a chemistry problem

91. When determining the impurity of Ni in salt Co, a sample of the last mass of 2.3520 g was dissolved, the necessary reagents were added - HCl, gelatin, pyridine - and diluted to 50 ml. A 25 ml aliquot of the solution was polarographed and a diffusion current of 2.5 μA was obtained. Then, 5 ml of a standard solution containing 1.00 • 10–2 mol/l NiCl2 was added to the polarographic cell and a diffusion current of 4.9 μA was obtained. Calculate the mass fraction of Ni in the preparation.