The mineral rhodochrosite [manganese(II) carbonate, MnCO_3] is a commercially im

Question

The mineral rhodochrosite [manganese(II) carbonate, MnCO_3] is a commercially important source of manganese. Write a half-reaction for the oxidation of the manganese in MnCO_3 (s) to MnO_2 (s) in neutral groundwater where the carbonate containing species in the product is HCO^-_3 (aq). Add H_2O and H^+ to balance the H and O atoms in the equation. Do not add electrons, you may leave the half-reaction unbalanced with respect to charge. Include phases in the balanced chemical equation. Type an open parenthesis "(" to add a phase. Phases should not be subscripted. Use the left and rightarrow keys to move the cursor out of a superscript or subscript in the module.

Explanation / Answer

The unbalanced equation is:
MnCO3 ----------> MnO2 + HCO3-

oxidation number of Mn changes from +2 in MnCO3 to +4 in MnO2 , so two electrons must be added to the right.
MnCO3 ----------> MnO2 + HCO3- + 2e-

Now , we have a total of charge -3 ( one negative charge on HCO3- and 1 negative charge on each electrons so total -3 charge) on the right side verses no charge on the left.To balance this add 3 H+ on the right ( -3 + 3 = 0) this will give right side also with no charge
MnCO3 ----------> MnO2 + HCO3- + 2e- + 3H+

now add H20 to balance the H and O atoms
MnCO3 + 2H20 ----------> MnO2 + HCO3- + 2e- + 3H+

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