Question

14 H+ + 6 Fe2+ + Cr2O72- . 2 Cr3+ + 6 Fe3+ + 7 H2O This reaction is used in the

titration of an iron solution. What is the concentration of the iron solution if it takes 45.20 mL

of 0.1000 M Cr2O72- solution to titrate 50.00 mL of an acidified iron solution?

a.

0.5424 M

b.

0.1000 M

c.

1.085 M

d.

0.4520 M

e.

0.2712 M

Answer 1

Option A 0.5424 M

Step-by-step explanation:

To do this, let's write the reaction again and see the mole ratio:

14H⁺ + 6Fe²⁺ + Cr₂O₇⁻ ---------> 2Cr³⁺ + 6Fe³⁺ + 7H₂O

According to this reaction, we have a mole ratio between the dicromate and iron of 1:6. In other words, 6 moles of dicromate reacts with only 1 mole of iron, therefore we can use the following expression:

nFe = 6 * nCr₂O₇

This is a REDOX reaction, where Iron is being oxidized while cromium is being reduced. Now, we have the concentrations and volume, let's express the moles in function of concentration and volume:

M₁V₁ = 6M₂V₂

Replacing the given data above and solving for concentration of iron (M₁)

M₁ = 6 * 45.20 * 0.1 / 50

M₁ = 0.5424 M

This is the concentration of the iron solution