1st century A sample of ore weighing m g was dissolved and, after appropriate treatment, Fe2+ ions were titrated with a solution of potassium permanganate using the photometric method. Construct a titration curve and calculate the mass fraction of iron in the sample based on the following measurement results:

Option Weight of sample m, g Concentration of KMnO4 solution Optical density of solution after
addition, ml KMnO4
10.00
ml 12.00
ml 14.00
ml 15.00
ml 18.00
ml 20.00
ml
1 1.0389 0.1075 n. (feq.= 1/5) 0.010 0.010 0.010 0.050 0.100 0.150



Answer: 1) 8.32%; 2) 7.00%; 3) 6.83%.

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