Question

Give reasons for the following:
(a) Aluminium foils are used to wrap food items.
(b) Immersion rods for heating liquids are made up of metallic substances.
(c) Copper cannot displace zinc from its salt solution.
(d) Sodium and potassium are stored in kerosene.

Answer 1

Hint:
(a) Aluminium foils are used to wrap food items as aluminium is malleable and less reactive.
(b) Immersion rods for heating liquids are made up of metallic substances due to good electrical and thermal conductivity.
(c) Copper cannot displace zinc from its salt solution as zinc is a stronger reducing agent than copper.
(d) Sodium and potassium are stored in kerosene to avoid exposure with air, to prevent fire.

Complete answer:
(a) Among metals, aluminium has less reactivity. There is no reaction between aluminium metal with food items. Due to this, the taste of food is unaltered. Aluminium metal has high malleability and ductility. As aluminium metal has high malleability, it can be easily transformed into very thin aluminium foils. These very thin aluminium foils are ideal for raping food. Hence, aluminium foils are used to wrap food items.

(b) Metals have good electrical and thermal conductivity. When you use immersion rods for heating liquids, the material of the immersion rod should be such that you can pass electricity through this material, and upon passage of electricity, heat should be generated within this material. Then this heat should be transferred to the liquid being heated. For this, the material of the immersion rod should have good electrical and thermal conductivity. Hence, immersion rods for heating liquids are made up of metallic substances.

(c) Copper cannot displace zinc from its salt solution.
But zinc can displace copper from its salt solution. This is because copper has less reactivity than zinc. In the electrochemical series, zinc is placed below copper. Hence, zinc is a stronger reducing agent than copper. Due to this, zinc can reduce cupric ions to copper.

(d) Sodium and potassium metals have very high reactivity. When they are kept in open, they come in contact with the atmosphere and undergo a spontaneous reaction. Due to this vigorous reaction, sodium and potassium quickly catch fire due to exposure to air. You can prevent this from happening if you store sodium and potassium in kerosene. Sodium and potassium are covered with kerosene so that they cannot come in contact with air. This prevents accidental fire.

Note:
(a) Malleability is the phenomenon in which metal can be drawn into thin sheets. Ductility is a phenomenon whereas metal can be drawn into wires.
(b) Metals have good electrical and thermal conductivity as the valence electrons are free to move throughout the metal.
(c) A reducing agent supplies electrons to other substances. The reducing agent itself is oxidized in the process.
(d) Alkali metals are highly reactive as they have very low ionization energies.