Question

Which of the following is true for ionic solids?
(A) Ionic solids have high vapour pressures because they have very strong intermolecular forces holding the molecules together in a crystalline structure.
(B) Ionic compounds are excellent conductors of electricity because they are composed of electrically charged ions and conductivity involves charged particles.
(C) Polar solvents are the best choices to dissolve ionic compounds because those solvents have permanent charge separations like the ions in an ionic crystal structure.
(D) Ions with a bigger atomic radius tend to be more strongly attracted to each other because there are more electrons to be attracted to the nucleus of other atoms.

Answer 1

Hint: There are broadly two types of compounds, ionic compounds and organic compounds. Ionic compounds are solid at room temperature and are composed of ions held together by electrostatic forces of attraction in a crystal lattice.
Complete step by step answer:
Ionic solids consist of oppositely charged ions that are arranged in a three dimensional crystalline structure at room temperature. The ions have uneven atomic size and there exists a strong electrostatic force between the ions which makes them electrically inert in their solid state. Because of the presence of strong electrostatic force in between the oppositely charged ions they are never found in gaseous or liquid state under normal temperature and pressure conditions as the ions lack mobility.
The ionic solids have low volatility along with high melting as well as boiling points. This results because of the strong electrostatic force existing in between the cations and the anions which holds them in fixed positions. Even in the molten state, they have low vapour pressure since in the molten state long range electrostatic forces of attraction which hold the molten state together.
In the solid state, the ionic compounds do not conduct electricity. This is mainly due to the presence of strong electrostatic force in between the ions due to which they are not mobile and hence show no conduction in the solid phase.
However, when they are in solution or in fused state they show high conductance. This is because as we increase the temperature, the ions acquire kinetic energy. When this kinetic energy overcomes the strong electrostatic forces of attraction existing between the ions, the compound melts. Similarly when ionic solid is dissolved in an ions solution, the solution enthalpy overcomes the electrostatic forces of attraction existing between the ions and the ions become separated from one another and become mobile. They become free and move about under the influence of the applied electric field.
“The solubility in polar and non-polar solvents depends upon the presence of electrostatic force which exists in between the cations and anions”. If a solvent has a high dielectric constant which is generally the case with polar solvents, these forces get reduced which in turn helps the ions move freely and form the solvated ions. Since non-polar solvents have low dielectric constants, ionic solids are insoluble in non-polar solvents.
Ions with bigger atomic radius tend to be weakly attracted due to their large ionic radius. Also as the size of the ions increases, the nucleus will have weak hold onto the electrons present in the outermost shell due to the shielding effect offered by the inner electrons.
Therefore option (c) Polar solvents are the best choices to dissolve ionic compounds because those solvents have permanent charge separations like the ions in an ionic crystal structure is the correct answer.
Note: There are some ionic solids that show properties different from what is generally shown by the ionic solids. These ionic compounds are generally composed of larger ions and are called ionic liquids, since they have a melting point below or near the room temperature.