Using standard electrode potentials
In this section you will be using the list of half-equations and standard reduction potentials from your data sheet.
A few basic rules to start:
- The half-equations are all reversible.
- They are shown with the oxidised form on the left and the reduced form on the right.
- A forward reaction on this list is a reduction reaction.
- A reverse reaction on this list is an oxidation reaction.
- The reduction potentials are the voltages (EMFs) produced under standard conditions relative to the hydrogen half-cell.
Understanding the list of standard reduction potentials
From these rules you should be able to answer the following questions. Write the answers in your notes and then check your answers.
1. What would be the direction of a reduction reaction on this list?
2. What would be the direction of an oxidation reaction on this list?
3. On which side of the list are oxidising agents (oxidants) shown?
4. On which side of the list are reducing agents (reductants) shown?
Click here to check your answers
1. Reduction reactions are the forward reactions.
2. Oxidation reactions are the reverse reactions.
3. Oxidising agents (oxidants) are on the left side.
4. Reducing agents (reductants) are on the right side.
Oxidants and reductants
Remember that the value of the reduction potential shows the strength of the force that can be caused by the chemical process occurring. A high positive value is an indication that the reaction shown is very likely to occur.
Fluorine as the 'king of the oxidants'
Look at the value of the reduction potential for Fluorine (F2). It is by far the highest. This indicates that fluorine molecules combine with electrons with a high amount of 'force'. This makes fluorine an extremely strong oxidising agent, as it will 'strip' electrons from just about any other species.
On your paper copy of the reduction potentials, highlight the other common oxidising agents that were listed in the 'Common oxidants and reductants' section.
- What do you notice about the position of these oxidants on the list?
- Why do you think this is?
- What can you say about the strength of hydrogen peroxide as an oxidant?
Answers and hints
All the common oxidants are in the top half of the left-hand side.
To be an effective oxidising agent, a relatively high reduction potential is required.
Hydrogen peroxide is a very strong oxidant.
In general, the higher up the list, the greater the strength of the oxidising agents.
Remember that these values are based on standard conditions (25 °C, 1.00 atm and 1.00 mol L-1 concentration)
Activity: What about the reductants?
Go back to the list of common reducing agents and highlight their position on the same list. (Use a different colour for the reductants.)
Remember that reductants are themselves oxidised in the process of reducing another chemical.
Now answer the following true/false questions.
1 |
Potassium metalPotassium is the strongest reducing agent shown on the list. |
2 |
Strongest reducing agent?In standard conditions, iron metal is a stronger reducing agent than aluminium. |
3 |
HydrogenHydrogen ions act as reducing agents. |
4 |
Iron(II) compoundsIron (II) salts can act as oxidants and reductants. |
By now you should have a version of the standard electrode potentials with some of your additional notes. To this version add some other labels to show the following:
- the hydrogen half-cell used as a reference
- the trend in strength of oxidising agents
- the trend in strength of reducing agents.
Use your version to answer the following questions.
5 |
6 |
7 |
8 |
If you are able to answer these questions you are getting used to using the list of reduction potentials. If you are getting some wrong, go back to the basic rules at the start of the section.
You may want to access this version of the list 
to use in the future.
Now that you have an idea of how the list of reduction potentials can provide information about oxidants and reductants, you should be able to move on to use this information to predict how chemicals will react with each other. This is the most important part of this topic and is covered in the next section.
