To find the concentration of Fe2+ in part (a), we can use the balanced equation to determine the mole ratio between Fe2+ and K2Cr2O7. From the balanced equation, we can see that the mole ratio between FeSO4 and K2Cr2O7 is 6:1.
Step 1: Calculate the moles of K2Cr2O7 used in the titration
Moles of K2Cr2O7 = Molarity x Volume (L)
= 0.250 mol/L x 0.02185 L
= 0.0054625 mol
Step 2: Determine the moles of Fe2+ in the reaction
From the balanced equation, 6 moles of FeSO4 react with 1 mole of K2Cr2O7
So, moles of Fe2+ = 0.0054625 mol x (6 mol FeSO4 / 1 mol K2Cr2O7) = 0.032775 mol
Step 3: Calculate the concentration of Fe2+
Molarity of Fe2+ = Moles / Volume (L)
= 0.032775 mol / 0.0300 L
= 1.09 mol/L
= 1.09 M Fe2+
For part (b), we can use the molar mass of Fe2+ and the mass of the original sample to calculate the mass percent of iron in the ore.
Step 1: Calculate the moles of Fe2+ in the original sample
Moles of Fe2+ = Mass / Molar Mass
= 2.58 g / 55.845 g/mol
= 0.04622 mol
Step 2: Calculate the mass percent of iron in the ore
Mass percent = (mass of Fe2+ / Total mass of sample) x 100%
= (0.04622 mol x 55.845 g/mol / 2.58 g) x 100%
= 70.9% iron in the ore
Therefore, the mass percent of iron in the original sample of iron ore is 70.9%.
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?
• Answer: 70.9%
1 answer
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