To 100.0 of a solution that contains 0.120 and 0.420 is added 30.0 of 0.220. The

Question

To 100.0 of a solution that contains 0.120 and 0.420 is added 30.0 of 0.220. The dichromate and chromium(II) ions react to give chromium(III) ions.Write a balanced net ionic equation for the reaction.

Explanation / Answer

1. Balance the number of chromium atoms on both sides of the reaction. Cr2O72-(aq) => 2 Cr 3+ (aq) 2. Add sufficient water molecules to balance the number of oxygen atoms. Cr2O72-(aq) => 2 Cr3+(aq) + 7 H 2O (l ) 3. Add sufficient hydrogen ions to balance the hydrogen in the water molecules. Cr2O72-(aq) 4. Add the correct number of electrons to balance the total charge on each side. Cr2O72-(aq) The above ion-electron equation is now balanced and shows the reduction of dichromate to chromium(III) ions. Cr2O72-(aq) + 14 H+ (aq ) => 2 Cr3+(aq) + 7 H2O(l) + 14 H+(aq) +6e => 2 Cr3+(aq) + 7 H2O(l) + 14 H+(aq) +3 Sn2+(aq) => 2 Cr3+(aq) + 7 H2O(l) + 3 Sn4+(aq) Redox

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