125. Solving a chemistry problem

2. For the polarographic determination of folic acid in a medicinal preparation, a weighed portion of the preparation weighing 0.0570 g was dissolved in 50 ml of a 0.05 mol/l sodium carbonate solution, 5 ml of the resulting analyzed solution was taken, 5 ml of a 0.05 mol/l solution was added to it sodium carbonate, 10 ml of a 0.1 mol/l solution of ammonium chloride in 30% alcohol and received 20 ml of the test solution. This solution was placed in a thermostatically controlled ( 25 + 0.5 C) polarographic cell, a current of gaseous nitrogen was passed through the solution (to remove dissolved oxygen). Conducted polarography of the test solution and received a polarogram with a polarographic wave height h=28.
A portion of 0.0500 g of folic acid standard was dissolved in 50 ml of 0.05 mol/l sodium carbonate solution. From this solution volumes V equal to 3,4,6,7 and 8 ml were successively taken, the volume of each solution of ammonium chloride in 30% alcohol was adjusted and 5 standard solutions were obtained. Under the same conditions, polarography of standard solutions was carried out and the following results were obtained:
V, ml 3 4 6 7 8
h 15 20 30 35 40
Determine the mass fraction (in %) of folic acid in the medicinal product using the methods of the calibration curve and standard solutions.