Consider the equation below: \(\mathrm{Cr_2O_7^{2-} + 6Fe^{2+} + 14H^+ \rightarrow 2Cr^{3+} + 6Fe^{3+} + 7H_2O}\). The oxidation number of chromium changes ...

Assessment: JAMB UTME - Chemistry - 2019 Subject: Chemistry

Question 1 Report

Consider the equation below:

\(\mathrm{Cr_2O_7^{2-} + 6Fe^{2+} + 14H^+ \rightarrow 2Cr^{3+} + 6Fe^{3+} + 7H_2O}\).

The oxidation number of chromium changes from

+5 to +3

+6 to +3

-2 to +3

+7 to +3

Answer Details

Cr

_{2}

O

_{7}^{2 -}

+ 6Fe

^{2 +}

+ 14H

^{+}

\to

2Cr

^{3 +}

+ 6Fe

^{3 +}

+ 7H

_{2}

O
The oxidation of Cr in Cr

_{2}

O

_{7}^{2 -}

:
Let the oxidation of Cr = x;
2x + (-2 x 7) = -2

⟹

2x - 14 = -2
2x = 12 ; x = +6
Hence, the change in oxidation of Cr = +6 to +3

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