Explain with values and reactions from standard reduction potentials tables why neither gold (I) nor gold (III) not to mention the base metal itself, tarnishes (that is can be oxidized by exposure to air)
Look up the oxidation potential for Au and Au^+ and Au^3+
Au ==> Au^+ + e Eo = -1.68
Then look up the reduction potential for oxygen.
O2 + 4H^+ + 4e ==>2H2O Eo = +1.229
If you add the oxidation potential of Au and the reduction potential for oxygen you get a negative number which means the cell is not spontaneous. That explains why Au (the base metal) is not oxidized by air. The same process can be used for Au^+ to Au^3+. The book I used is about 50 years old (what does that tell you?) so you should use your resources to make sure of the numbers. I expect they have changed, at least a little.
Thank you very much. This helps a great deal
To understand why gold (I), gold (III), and gold itself do not tarnish when exposed to air, we need to analyze their standard reduction potentials.
In electrochemistry, the term "standard reduction potential" refers to the tendency of a substance to be reduced (gain electrons) in a redox reaction. It is measured relative to the standard hydrogen electrode (SHE), which is assigned a potential of 0 volts.
Gold (I) ions (Au⁺) have a standard reduction potential of +1.68 V, while gold (III) ions (Au³⁺) have a standard reduction potential of +1.50V. These positive values indicate that both gold oxidation states have a strong tendency to be reduced, meaning they are not easily oxidized themselves.
On the other hand, base metals like iron, copper, and silver have negative standard reduction potentials, indicating a strong tendency to be oxidized (lose electrons) in a redox reaction. For example, iron (Fe²⁺) has a standard reduction potential of -0.44 V, copper (Cu²⁺) has a standard reduction potential of +0.34 V, and silver (Ag⁺) has a standard reduction potential of +0.80 V.
When gold or gold compounds are exposed to air, they are in contact with oxygen, which is present in the atmosphere. However, gold's positive standard reduction potentials indicate that it does not have a strong tendency to be oxidized by oxygen. In other words, gold (I), gold (III), and gold metal are relatively stable and resistant to oxidation.
In contrast, metals like iron, copper, and silver have negative standard reduction potentials, which means they are more readily oxidized by oxygen. This oxidation leads to the formation of metal oxides or other compounds, commonly known as tarnish.
In summary, the reason why gold (I), gold (III), and gold itself do not tarnish when exposed to air is due to their positive standard reduction potentials, which indicate a low tendency to be oxidized.