Predicting Redox
9.3
Demo
• Mg + Cu2+ ____________
vs
Cu + Mg2+ ___________
• Why did 1 reaction go and the other not?
• How did you predict the products?
Lets Look Closer
• Mg + Cu2+ Mg2+ + Cu
• Mg Mg2+ + 2e-
Oxidized
• Cu2+ + 2e- Cu
Reduced
Reactivity Series
Strength of an oxidizing agent
is similar to strength of an
acid. Acids accept protons,
oxidizing agents accept
electrons
• Scientists did testing and compared oxidizing agents strength
• Using this information scientist produced the standard reduction potential
table.
• If a compound is a strong oxidizing agent its conjugate is usually a weak
reducing agent (and vice versa)
• Some elements are multivalent and are more flexible (can have a charge or
+1 or +2)
Eo os called reduction potential
and shows the strength of the
oxidizing agent
Notice: Most reactive cations
and non-metals are strongest
oxidizing agent
Half reactions in table
are always written as a
reduction
Notice: Most reactive metals are
strongest reducing agents
Spontaneity
• A redox reaction occurs
only if the oxidizing agent
is above the reducing
agent in the table.
• Zn + Cu2+
Vs
• Cu + Zn2+
Example
• Determine if the following reaction occurs. If so write a balanced equation,
and appropriate half reactions
• Cl2 + NaBr
Example 2
• A chemist finds a waste container that contains the following ions and
compounds. What is the predominant redox reaction (hint find the strongest
oxidizing and reducing agents)
• Cl2, Ag+, Sn2+, and I1-
Titration
• Remember Titration: is a quantitative analysis method used to determine the
concentration of an unknown solution by reacting with another substance of
known concentration.
• You can titrate with a strong oxidizing or reducing agent.
• Indicator: is usually a reducing agent with a different colour when oxidized.
• We want the indicator to be a weaker OA/RA so it changes colour when the strong
OA/RA is consumed.
Indicator
• MnO4- in acidic
conditions
becomes Mn2+
which is pink
Titration Example
• To titrate a 25mL solution of Fe2+ to the equivalence point required 16.7mL
of 0.0152MnO4- (in acidic solution). What is the concentration of Fe2+?
Fe2+ + MnO4-+ H+ __________________________
(use your chart to predict what will form)