7. To construct a calibration graph for the determination of manganese, a 10-4 M solution of manganese(II) salt was used, aliquots of which were diluted with a buffer solution to 25 cm3 and polarographed. The following data was obtained:
V, cm3 1 2 3 4 5 6
H, ml 9 16 26.5 35 41 54
A mass of 0.5 g of alloy containing manganese was dissolved in 100 cm3 of nitric acid, 5 cm3 of the resulting solution was taken and diluted with the same buffer solution to 25 cm3. When polarography was performed, a wave height of 32.7 was obtained. Calculate the mass fraction of manganese in the alloy.

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