Question

Explain the following

1. Reactivity of Al decreases if it is dipped in HNO₃
2. Carbon cannot reduce the oxides of Na or Mg
3. NaCl is not a conductor of electricity in solid state whereas it does conduct electricity in aqueous solution as well as in molten state
4. Iron articles are galvanised.
5. Metals like Na, K, Ca and Mg are never found in their free state in nature.

Answer 1

1. Reactivity of aluminium decreases if it is dipped in nitric acid because it is a strong oxidizing agent. When aluminium is dipped into nitric acid a layer of aluminium oxide gets deposited on top of the aluminium article because of which reactivity of aluminium gets reduced.
2. Oxides of sodium and magnesium are very strong oxides and carbon is not a very strong reducing agent hence, carbon cannot reduce the oxides of sodium and magnesium.
3. In the solid-state, sodium chloride does not contain any free ions and thus is not able to conduct electricity. Whereas in the molten or aqueous state free moving ions of sodium chloride causes the conduction of electricity.
4. Iron undergoes a slow but spontaneous process of corrosion which is known as rusting, in which the top layer of the article gets degraded over time. To prevent the process of rusting of iron a coat of zinc metal is put on top of the iron article which acts as a sacrificial element by undergoing corrosion and forms a passive oxide layer on top and thus, prevents the further corrosion of the zinc layer and in doing so it prevents the rusting of iron.
5. Metals like sodium, potassium, calcium and magnesium are very reactive metal and thus have a very high affinity for a reaction with oxygen gas present in the atmosphere. That is why these metals are never found in their free state in nature.