81. Solving a chemistry problem

15. For the chromatographic determination of copper on paper impregnated with an ammonia solution, three standard solutions were prepared. To do this, a sample of CuSO4*5H2O weighing 0.2780 g was dissolved in a 100 ml volumetric flask. Then 5.0 was taken from this flask; 25.0; 50.0 ml and diluted in 100 ml flasks. A weighed sample of 2.5000 g, containing Cu2 ions, was also diluted in a 100 ml volumetric flask. Determine the mass content of copper ions in the test sample, if the area of ​​the spots of standard solutions was respectively: 2.0; 11.0; 21.0 mm2, and the spot area of ​​the test solution is 14.0 mm2.