Question

Explain the factors affecting melting point.​

Answer 1

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Explain the factors affecting melting point.

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1. External Pressure: Normal solids, e.g. iron, copper and wax, expand when they change into liquids. When pressure is applied on the surface of a normal solid, expansion is suppressed and melting is delay. Thus, the melting point of a normal solid is raised. Solids, like ice and bismuth, contract on melting into liquids. When pressure is applied on the surface of such a solid, the change into the liquid is assisted. Thus, the melting point of ice is lowered by the application of pressure.

2. Presence of H-bonding: The intermolecular hydrogen bonding (in water, ammonia etc) and The intramolecular hydrogen bonding (in Salicylic acid, o-nitrophenol etc) keeps the molecules closer due to dipole –dipole intermolecular force.

3. Type of bonds present in molecules: Ionic bonds are stronger than covalent bonds so materials with ionic bonds will have higher melting point.

4. Presence of other substance: Presence of ice or lipid changes the melting point of water or presence of Urea in Benzene.

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Answer 2

Answer:

The factors affecting melting point are :

1. Effect of pressure : The effect of pressure on the melting point of the solids depends upon the nature of the solid. For solids which expand on melting, increase in pressure increases the melting point. This is because increase in pressure opposes expansion. Example - Paraffin, wax, silver, gold, copper, etc.

For solids which contract on melting, increase in pressure favours contraction.

Examples - Ice, cast iron, brass, etc.

2. Effect of addition of impurities : Addition of impurities to a solid decreases the melting point of the solid thereby allowing the substance to melt at a lower temperature.

Example - Rose's metal, an alloy of tin, lead and bismuth.