Standard Oxidation Potentials
Over the years chemists have made comparisons and measurements of the ability of chemicals to lose electrons. Those comparisons have been compiled into a standard oxidation potential list. One such list is given in example 16 in your workbook and on the SOP List page in this section. If you to take a look at the one in your workbook you will be able to refer to it while you read this page.
Comparison with Expectations
So you can see that our rating of the ease of oxidation for these chemicals was not bad. The uncertain order of sodium and calcium is established. (The reason for calcium being higher is primarily that the calcium ions have a higher charge and smaller size than sodium ions and thus form stronger more stable bonds to water molecules.) The uncertain position of aluminum is also established. You can see that the general trend for the ease of losing electrons fits in pretty well with what can be deduced about the ease of oxidation and reduction from the position of an element on the periodic table.
This oxidation potential list does more than just list the chemicals in order of their ease of oxidation. On the right hand side of the list there is a numerical rating (or measure) of their ease of oxidation, EMF or Eo. It is measured in volts compared to an arbitrary standard.
This standard oxidation potential list is far from a complete list. There are many, many reactions. This is just a sampling.
You should notice in the list in your workbook that some lines include more than one chemical. If the oxidation rating is based on the presence of some other chemical in the reaction, that chemical is listed there, too. Two examples are that lead is more easily oxidized in the presence of sulfate ion and gold is more easily oxidized in the presence of chloride ion. (That is part of the reason why aqua regia can dissolve gold.)
The phrase standard oxidation potential deserves a bit of explanation.
If the concentrations, temperature or pressure are different , then the voltage associated with that particular half-reaction will be different.
E-mail instructor: Eden Francis
Clackamas Community College