To calculate the mass percent of iron in the ore, we need to determine the moles of FeSO4 used in the titration and then convert it to grams of Fe and finally calculate the mass percent.
a)
1. Calculate the moles of K2Cr2O7 used:
Moles K2Cr2O7 = (0.250 M) x (21.85 mL / 1000 mL) = 0.0054625 mol
2. Using the balanced equation, the mole ratio of FeSO4 to K2Cr2O7 is 6:1, so the moles of FeSO4 used are:
Moles FeSO4 = 6 x Moles K2Cr2O7 = 6 x 0.0054625 mol = 0.032775 mol
3. Calculate the concentration of Fe2+:
Volume of FeSO4 solution used = 30.0 mL
Moles Fe2+ = 0.032775 mol
Concentration Fe2+ = Moles Fe2+ / Volume FeSO4 solution (L) = 0.032775 mol / (30.0 mL / 1000) = 1.09 M
b)
1. Calculate the moles of Fe in 2.58 g of iron ore:
Molar mass of FeSO4 = 55.85 g/mol + 32.06 g/mol + 4(16.00 g/mol) = 151.06 g/mol
Moles FeSO4 in 2.58 g = 2.58 g / 151.06 g/mol = 0.0171 mol
2. Calculate the moles of Fe:
From the balanced equation, 6 mol FeSO4 produces 3 mol Fe
Moles Fe = 0.0171 mol x (3 mol Fe / 6 mol FeSO4) = 0.00855 mol
3. Calculate the mass percent of Fe in the ore:
Mass of Fe = Moles Fe x Molar mass of Fe = 0.00855 mol x 55.85 g/mol = 0.477 g
Mass percent of Fe = (0.477 g / 2.58 g) x 100% = 18.5%
Therefore, the mass percent of iron in the ore is 18.5%.
Tutorial Question
• Q1.The amount iron in an iron ore is determined by
converting the Fe in FeSO4
, followed by titration with a
solution of K2Cr2O7
. The balanced equation is
• 6FeSO4
(aq) + K2Cr2O7
(aq) + 7H2SO4
(aq) →
3Fe2
(SO4
)3
(aq) + Cr2
(SO4
)3
(aq) + 7H2O(l) + K2SO4
(aq)
• a) What is the concentration of Fe2+, if 21.85 mL of 0.250
M K2Cr2O7
is required for titration of 30.0 mL of FeSO4
solution? Answer: 1.09 M Fe2+
• b) If the original sample of iron ore had a mass of 2.58 g,
what is the mass percent of iron in the ore?
1 answer
1 answer