140. Solving a chemistry problem

53. A sample of fertilizer weighing 2.00 g was treated by boiling with a saturated solution of ammonium oxalate; after cooling, the solution was diluted in a volumetric flask with a capacity of 500.0 ml and filtered. Aliquot of filtrate volume 5.00 10
ml was diluted to 250.0 ml. The resulting solution was photometric in flame in the same way as standard solutions prepared from KCl. Photometric data
are shown in Table 10.

Parameter Standard solution
1 2 3
CK, mg / l 5.0 10.0 15.0
I * rel 8.0 15.0 24.2
I * rel = 18.4

Build a calibration graph and determine the mass fraction (%) of potassium in the fertilizer according to the data in Table 11 (in accordance with the task number).