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Balancing redox equations by the oxidation number method

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2KMnO4 + 5H2O2 + 6HCl --> 5O2 + 2MnCl2 + 8H2O + 2KCl

I need to calculate the balanced NET IONIC equation for the above reaction.

I've been using the oxidation number method and determined H2O2 is the reducing agent and KMnO4 is the oxidizing agent.

Mn gained 5 electrons, but I'm not sure how many electrons Oxygen gained, I'm thinking one electron but the two different oxygen oxidation numbers in the products are throwing me off. I know I need to make the electrons lost equal the electrons gained. My problem is that I'm not sure about the number of oxygen electrons gained and then I'm not sure on which compounds containing oxygen I should apply the coefficient to.

Am I even using the right approach?

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Solution Preview

To answer this question one must first assign oxidation states for each individual element. Potassium (K) is a spectator, along with Cl, and H takes no part in the redox reaction. We can see that Mn gains 5 electrons, and it must do so by taking them from the peroxide (HOOH). What I would do is to separate both the oxidation and the reduction, and ...

Solution Summary

This answer is provided in 288 words and explains how to balance an equation using oxidation states and step-by-step balancing of the reaction.

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Cell Potentials and Balancing Redox Equations

Please see the attached file for the fully formatted problems.

Question 1.
In addition to mass balance, oxidation-reduction reactions must be balanced such that the number of electrons lost in the oxidation equals the number of electrons gained in the reduction. This balancing can be done by two methods: the half-reaction method or the oxidation number method. The half-reaction method balances the electrons lost in the oxidation half-reaction with the electrons gained in the reduction half-reaction. In either method , , and may be added to complete the mass balance. Which substances are used depends on the reaction conditions.

Acidic solution

In acidic solution, the bromate ion can be used to react with a number of metal ions. One such reaction is

Since this reaction takes place in acidic solution, and will be involved in the reaction. Places for these species are indicated by the blanks in the following restatement of the equation:

BrO_3^- (aq)+ Sn^(2+) (aq)+ ____→Br^- (aq)+Sn^(4+)(aq) + ______

Question 2.
Calculate the standard cell potential at 25C for the following reaction:
Mg(s) +Fe2+(aq) -> Mg2+(aq) + Fe(s)
when H=-617 kJ and S= -301J/K.

E = ________V

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