27. Solving a chemistry problem

41. A sample of silicate weighing 0.2000 g was dissolved in a mixture of acids, the solution was evaporated, the residue was treated with hydrochloric acid and transferred to a 200 ml volumetric flask. Determination of sodium in the sample was carried out using a calibration graph method. Before measurement, the analyzed solution was diluted 2 times. Photometric data is given below:
СNa, mg/l 2.5 5.0 7.5 10
I, µA 10 20 30 40
Analyzed solution I = 41.