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Using the half cell method to balance a redox reaction

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Balance the following redox reaction using the half cell method for balancing redox reactions:

KClO_3(aq) + HBr(aq) -----> Br2(l) + H_2O(l) + KCl

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Please see attachment for detailed tutorial and solution. The attachment is copied below in case there are problems opening the attachment, but the attachment is much easier to read, as the subscripts and superscripts are correct.

Problem: Balance the following redox reaction:

KClO3(aq) + HBr(aq) -----> Br2(l) + H2O(l) + KCl(aq)

When balancing a redox reaction, there are several steps that need to be followed. This is because we not only have to balance the number of elements on each side of the reaction, as is necessary when balancing all other reactions, but we also have to balance the electrons transferred.

The aim of this tutorial is to demonstrate the half-cell method of balancing equations. The steps that you want to follow to balance this equation are as follows.

In acidic solution:

Balance all non-hydrogen and non-oxygen atoms in the equation.

In our reaction, this is done by placing a 2 in front of the HBr. Remember that when balancing, we can only alter coefficients, NOT subscripts.

KClO3(aq) + 2HBr(aq) -----> Br2(l) + H2O(l) + KCl(aq)

Split your reaction into two half reactions. You should consider the species oxidized and the species reduced in two separate reactions.

The two half-reactions for our reaction are:
KClO3(aq) ----> KCl(aq)


2 HBr(aq) -----> ...

Solution Summary

The expert uses the half cell method to balance a redox reaction.

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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

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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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