A compound contains only Fe and O. A 0.2729 g sample of the compound was dissolved in 50 mL of concentrated acid solution, reducing all the iron to Fe2+ ions. The resulting solution was diluted to 100 mL and then titrated with a 0.01621 M KMnO4 solution. The unbalanced chemical equation for reaction between Fe2+ and MnO−4 is given below.
MnO−4(aq)+Fe2+(aq)→ Mn2+(aq)+Fe3+(aq) (not balanced)
The titration required 42.17 mL of the KMnO4 solution to reach the pink endpoint.What is the empirical fomula of the compound?

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pstnonsonjoku pstnonsonjoku · Answer 1 · 2020-10-14T05:17:57+02:00

Answer:

FeO

Explanation:

The balanced reaction equation is

MnO−4(aq)+5Fe2+(aq)→ Mn2+(aq)+5Fe3+(aq)

Number of moles of KMnO4 reacted = 0.01621 M × 42.17/1000 = 6.84 × 10^-4 moles

Since

1 mole of MnO4^- reacted with 5 moles of Fe^2+

6.84 × 10^-4 moles of MnO4 will react with 6.84 × 10^-4 moles × 5 = 34.2 × 10^-4 moles of Fe^2+

Mass of Fe^2+ reacted = 34.2 × 10^-4 moles of Fe^2+ × 56gmol-1 = 0.192 g of Fe

Hence % of iron in the sample = 0.192/0.2729 × 100 = 70.4%

% of oxygen = (0.2729 -0.192)/0.2729 × 100 = 29.6%

Empirical formula of the compound is obtained by

70.4/56, 29.6/16

1.257, 1.85

Divide through by the lowest ratio

1.257/1.257, 1.85/1.257

1, 1

Hence the empirical formula is FeO