Balancing REDOX reactions

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					Balancing REDOX reactions

There are 2 ways to balance redox reactions… by oxidation # and
by half reactions. We will use the half reaction method.

Why can’t we just balance normally?: because most redox
reactions happen in acidic/basic solutions

FIRST OF ALL… learning how to balance half-reactions properly:

Example #1 (acidic solution): Nitrous acid (HNO2) can be reduced
in an acidic solution to form nitrogen monoxide gas. What is the
reduction half-reaction of nitrous acid?
STEPS:
1.   Write reactants and products and balance all atoms other
     than oxygen and hydrogen
2. Balance oxygens with water molecules
3. Balance hydrogens with H+ ions
4. Balance charges by adding electrons to the more positive side
     of the equation
Example #2 (basic solution): Copper metal can be oxidized in a
Basic solution to form copper (I) oxide. What is the half-reaction
for this process?

STEPS:
1. Assume that the solution is ACIDIC and follow the steps just
learned.
2. Once the equation is mass + charge balanced, add the same
number of OH- ions as there are H+ ions to both sides of the
equation.
3. Combine equal numbers of H+ and OH- to make H2O’s
4. Cancel any H2O’s (or other molecules) that appear on both sides
of the equation.
Now you try: chlorine is converted to perchlorate ions in an acidic
solution. Write a half-reaction equation and state if it is
oxidation or reduction.




Balancing redox equations using half reaction equations:
-All equations have a reduction half and an oxidation half. So we
combine half reactions!

Example #1: in a chemical analysis, a solution of dichromate ions is
reacted with an acidic solution of iron (II) ions. The product
formed are iron (III) and chromium (III) ions as shown by the
following equation:;

Fe2+ + Cr2O7 2-  Fe3+ + Cr3+

Start by separating the above into 2 half-reactions, and treat as
we did before.
Example #1 continued

				
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posted:8/9/2012
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