0.800 g of an iron ore is dissolved and all the iron is converted to Fe^2+. It is titrated with 0.0200 M K2Cr2O7 in acidic medium, needing 28.0 mL. Find the percentage of Fe in the ore (Fe = 56), to one decimal place.

JEE Main levelNumerical answerDifficulty 2 of 3rx192

0.800 g of an iron ore is dissolved and all the iron is converted to $Fe X^{2 +}$ . It is titrated with 0.0200 M $K X_{2} Cr X_{2} O X_{7}$ in acidic medium, needing 28.0 mL. Find the percentage of Fe in the ore (Fe = 56), to one decimal place.

Numerical answer type, answer in %, tolerance 0.05.

mmol dichromate =

28.0 \times 0.0200 = 0.560

; each oxidises 6

Fe X^{2 +}

, so mmol Fe = 3.36. Mass =

3.36 \times 56 = 188.16

mg. Percentage = 188.16/800 x 100 = 23.52%.