Write the balanced chemical equation for the reaction. Include physical states.

Question

Aqueous sodium carbonate reacts with chromium(II) bromide to form aqueous sodium bromide and solid chromium(II) carbonate.

Write the balanced chemical equation for the reaction. Include physical states.

Answer 1

Sodium carbonate = Na₂CO₃

Chromium(III) bromide = CrBr₃

Sodium bromide = NaBr

Chromium(II) carbonate = CrCO₃

Na₂CO₃(aq) + CrBr₃(aq) ==> NaBr(aq) + CrCO₃(s)

Because Cr goes from 3+ on the left side of the reaction, to 2+ on the right side of the reaction, this shows that Cr was reduced (gained 1 electron). Therefore, something else must have been oxidized, but we see that Na, C, Br and O retain their original oxidation numbers on the product side, indicating nothing has been oxidized. How can this reaction take place? (Did I miss something here?)

The only way I see this would be is if you meant to write the product as chromium(III) carbonate, in which case that would be Cr₂(CO₃)₃(s) and then we can write the balanced equation as....

3Na₂CO₃(aq) + 2CrBr₃(aq) ==> 6NaBr(aq) + Cr₂(CO₃)₃(s)