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objectives
objectives
Understandings
An oxidizing agent is reduced and a reducing agent is oxidized.
The activity series ranks metals according to the ease with which they undergo oxidation.
Applications
Identification of the species oxidized and reduced and the oxidizing and reducing agents, in redox reactions.
Deduction of the feasibility of a redox reaction from the activity series or reaction data.
Predicting the Feasibility of a reaction
Predicting the Feasibility of a reaction
Once a reactivity series is constructed depending on the reduction or oxidation ability of each species, we can use it to predict the feasibility (probability) of a reaction occurring between any two pairs of reactants.
If one of the substances is a reducing agent - i.e. it reacts by losing electrons then this must react with an oxidising agent - i.e. a species that gains electrons.
Using Reduction Potentials
Using Reduction Potentials
Although this is a HL Skill (using the actual Reduction Values) using the Standard Potentials is actually an easier way to formulate Redox Equations that are FEASIBLE.
The rule is:
‘The Most Positive Species Oxidises the Least Positive Species’
Using Reduction Potentials - Example
Using Reduction Potentials - Example
To produce a redox equation we need to work out what is oxidised - and what is reduced.
How do we write the redox reaction between Cu and F using these values?
Write down both Reduction Equations
Cu+2 + 2e- → Cu
F2 + 2e- → 2F-
2. Which reaction is most positive? This means that this Species is Reduced
F2 + 2e- → 2F- +2.87V
3. Reverse the Reaction of the LEAST POSITIVE Reduction (so it is now oxidised)
Cu+2 + 2e- → Cu BECOMES
Cu → Cu+2 +2e-
4. Put both equations together - multiply each equation until both sides have EQUAL NUMBERS OF ELECTRONS
F2 + 2e- → 2F- (x1)
Cu → Cu+2 +2e- (x1)
5. Cancel out electrons and put both equations together
F2 + Cu → 2F- + Cu+2
Balancing Redox Reactions Activity
Balancing Redox Reactions Activity
Will the Following Reactions occur given the Reduction Potential data?
Ag+(aq) + Fe2+(aq) --> Ag(s) + Fe3+(aq)
Cr2O72-(aq) + 14H+(aq) + 6I-(aq) --> 2Cr3+(aq) + 7H2O(l) + 3I2(aq)
Cu(s) + Pb2+(aq) --> Cu2+(aq) + Pb(s)
2Fe3+(aq) + 2Br-(aq) --> 2Fe2+(aq) + Br2(aq)
2Cu+(aq) --> Cu2+(aq) + Cu(s)
Practical Activity - testing redox predictions
Practical Activity - testing redox predictions
Feasible - but not Spontaneous
Feasible - but not Spontaneous
although a reaction may be predicted as feasible it does not mean that it will happen spontaneously. If the activation energy is high then it may need an extra "push" to get it going. - for example the reaction between chlorine and hydrogen needs a spark or ultraviolet light and then it is explosively fast.
We call reactions that should be feasible but do not take place because of high Activation Energies Kinetically inert
Activity series practical
Activity series practical
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