Question

19. Give reasons for the following:
Electrovalent compounds are soluble in water, insoluble in organic solvents, good conductors of electricity
in molten or aq. solution state, have high melting points and undergo electrolytic dissociation on passage
of electric current, while covalent compounds are soluble in organic solvents, insoluble in water,
non-conductors of electricity, have low melting points & undergo ionisation on passage of electric current.​

Answer 1

Answer:

Electrovalent compounds dissolve in polar solvent like water because the forces of attraction between positive and negative charges become weak in water. But since covalent compound are made up of molecules, they do not ionize in water and hence do not dissolve in water.

Answer 2

Answer:

Electrovalent compounds

Solubility — Soluble in water, Insoluble in organic solvents.

Reason — Water [polar solvent] has a high dielectric constant i.e., capacity to weaken the force of attraction, thus resulting in free ions.

Organic solvents [non-polar] have low dielectric constants and do not cause dissolution.Conduction of Electricity — Good conductors of electricity in molten or aqueous solution state and in solid state, they are non-conductors.

Reason — Strong electrostatic force keeps ions in fixed position in the solid state. The force is weakened in the molten state and disappears in aqueous solution state, hence free ions formed migrate to oppositely charged electrodes.Melting Point — High melting point.

Reason — Strong electrostatic force of attraction between ions. Large amount of energy required to break the force of attraction.Dissociation — Undergoes electrolytic dissociation on passage of electric current.

Reason — Process involves separation of ions already present in the ionic compound.

E.g. NaCl ⇌ Na1+ + Cl1- [in molten state]

Covalent compounds

Solubility — Soluble in organic solvents [non-polar] but insoluble in water [polar].

Reason — Organic solvents [non-polar] e.g., the benzene, alcohol, dissolves non-polar covalent compounds [like dissolves like]. Water [polar solvent] cannot dissolve non-polar compounds, but dissolves polar.Conduction of Electricity — Non-conductors of electricity.

Reason — Non-polar compounds e.g., CCl4 contain molecules and not free ions. Hence, are non conductors. Polar covalent compounds e.g., HCl, NH3 show charge seperation and dissociate in H2O.Melting Point —Low melting points.

Reason — Weak Vander Waals force of attraction between molecules. Thus, less amount of energy is required to break these forces of attraction.Ionization — Undergoes ionization in solution state on passage of electric current. Process involves formation of ions from molecules which are not in ionic state.

E.g. HCl ⟶ H1+ + Cl1- [in solution state]