The mineral rhodochrosite [manganese(ii) carbonate, mnco3] is a commercially important source of manganese. write a half-reaction for the oxidation of the manganese in mnco3 to mno2 in neutral groundwater where the principal carbonate species is hco3–. add h2o, h+, and electrons as needed to balance the half-reaction.

MnCO3 + 2H2O ⇄ MnO2  + HCO3-  + 2e- +3H+

Explanation:

The unbalanced equation

MnCO3 ⇄ MnO2  + HCO3-

In MnCO3, the oxidation number of Mn is +2

In Mno2, the oxidation number of Mn is +4

The change from +2 to +4 requires an addition of  2 electrons (to the right side).

MnCO3 ⇄ MnO2  + HCO3-  + 2e-

The total charge now is -3 on the right side. To balance this we add 3 hydrogen atoms on the right side.

MnCO3 ⇄ MnO2  + HCO3-  + 2e- +3H+

On the right side we have 4 hydrogen atoms in total. On the left side we have 0 hydrogen atoms. So to balance, we have to add 2H2O on the left side

MnCO3 + 2H2O ⇄ MnO2  + HCO3-  + 2e- +3H+

Now the reaction is balanced.