Question

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.

Answer 1

To balance the half-reaction for the oxidation of manganese in MnCO₃ to MnO₂ in neutral groundwater, we derive the balanced equation MnCO₃ + H₂O → MnO₂ + 2HCO₃− + 2H+ + 2e−, ensuring mass and charge balance.

Step-by-step explanation:

The student is asking for a balanced half-reaction for the oxidation of manganese from manganese(II) carbonate (MnCO₃) to manganese(IV) oxide (MnO₂) in neutral groundwater, where the principal carbonate species is bicarbonate (HCO₃−). To balance the half-reaction for the conversion of MnCO₃ to MnO₂, we need to account for the changes in oxidation states and ensure mass and charge balance by adding H₂O, H+, and electrons as needed.

The balanced half-reaction is:

MnCO₃ + H₂O → MnO₂ + 2HCO₃− + 2H+ + 2e−

We start by writing the unbalanced half-reaction reflecting the change in the manganese species:

MnCO₃ → MnO₂

Next, we add water (H₂O) to balance the oxygen atoms and hydrogen ions (H+) to balance the hydrogen atoms. Finally, we balance the charges by adding the appropriate number of electrons (e−).

Answer 2

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

Step-by-step 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.