Question

What is corrosion? Do gold ornaments corrode? Justify.

Answer 1

Hint: Corrosion is when a refined metal is naturally converted to a more stable form. The corrosion of gold ornaments depends upon the extent of reactivity of gold in the surrounding environment.

Complete step by step solution:
Corrosion is one of the common phenomena that we observe in our daily lives. You must have noticed that some objects made of iron recovered with some reddish-brown or orange coloured layer at some point in time, which is the result of a chemical process known as rusting (corrosion).
Corrosion can be defined as the process through which refined metals are converted into more stable compounds such as metal oxides, metal sulphides, or metal hydroxides. The rusting of iron is the formation of iron oxides through the action of atmospheric moisture and oxygen.
Corrosion is an electrochemical process as it involves redox reactions between the metal and some atmospheric agents such as water, oxygen and sulphur dioxide.
Metals placed higher in reactivity series such as iron, zinc, etc. get corroded easily and metals placed lower in reactivity series like gold, platinum and palladium do not corrode. The explanation lies in the fact that this involves the oxidation of metals. Aluminium does not corrode like other metals though is reactive. Because aluminium is already covered by a layer of aluminium oxide. This layer protects it from further corrosion.
Factors affecting corrosion-
a. Exposure of metals to an atmosphere containing gases.
b. Exposure of metals to moisture, especially saltwater.
c. Presence of impurities like salt.
d. An increase in temperature increases corrosion.
e. Nature of the first layer of oxide formed.
f. Presence of acid in the air.
Gold-
In the periodic table, gold is one of the least reactive metals. It does not react with oxygen, so it never rusts or corrodes. Air, water, alkalis and all acids do not affect gold. The only exception is aqua regia (a mixture of hydrochloric acid and nitric acid) which can dissolve gold.
Gold is a noble metal in the periodic table, which is chemically inert and does not get corroded in the natural and industrial environment.

Thus, gold ornaments do not corrode in the natural environment.

Note: The degree to which items will rust or tarnish (tarnishing is also a form of corrosion) is then dependent upon the alloy or purity of gold (in carats).