Notes On Solubility Of A Solid In Liquid - CBSE Class 12 Chemistry

Solubility is defined as the maximum amount of solute that can be dissolved in a specified amount of solvent at a specific temperature.

Solubility is the interaction between particles of the solute and the solvent. Hence, it depends on the nature of the solute and the solvent, as well as on the temperature and pressure. But the solubility of solids in liquids is independent of pressure.

Solubility of solids in liquids:

The solubility of solids in liquids depends upon two factors,

  • Nature of the solute and solvent
  • The temperature


Nature of the solute and solvent:

In general "like dissolves like". Thus, a polar solute dissolves in a polar solvent and a non-polar solute dissolves in a non-polar solvent.

Therefore, polar (or) ionic molecules like sugar and sodium chloride dissolve in water molecules, which are polar, while non-polar molecules like naphthalene and anthracene dissolve in solvents like benzene and carbon tetrachloride, which are non-polar.

The solubility of ionic compounds is the result of the strong electrostatic interaction between the ions of the solute and the polar molecules of the solvent.

The solubility of non-polar solutes is the result of similar solute-solute, solute-solvent and solvent-solvent interactions.

When a solid solute is added to a solvent, its concentration in the solution increases. This process is known as dissolution.

On continuous addition of the solute, there will come a state where no more of the solute can be dissolved in the solvent at a given temperature Such a solution, is called a saturated solution.

A state of dynamic equilibrium is reached between the solute particles going into the solution and the solute particles separating out. The concentration of the solute in such a solution is its solubility.

If any more solute is added to a saturated solution, it gets separated out, and process is called precipitation.

A solution in which more solute can be dissolved at a specific temperature is called an unsaturated solution.


Solubility of a solute also depends on temperature:

Heat is required to break the bonds holding the molecules in the solid together. At the same time, heat is given off during the formation of new solute-solvent bonds.

If the heat liberated in the dissolving process is greater than the heat required to break the solid apart, the net dissolving reaction is exothermic in nature.

As per Le-Chatlier's principle, for an exothermic dissolution process, an increase in temperature inhibits the dissolving reaction, since excess heat is already being produced by the reaction.

If the heat given off in the dissolving reaction is less than the heat required to break the solid apart, the net dissolving reaction is endothermic.

As per Le-Chatlier's principle, for an endothermic dissolution reaction, more heat facilitates the dissolving reaction by providing energy to break the bonds in the solid.

Summary

Solubility is defined as the maximum amount of solute that can be dissolved in a specified amount of solvent at a specific temperature.

Solubility is the interaction between particles of the solute and the solvent. Hence, it depends on the nature of the solute and the solvent, as well as on the temperature and pressure. But the solubility of solids in liquids is independent of pressure.

Solubility of solids in liquids:

The solubility of solids in liquids depends upon two factors,

  • Nature of the solute and solvent
  • The temperature


Nature of the solute and solvent:

In general "like dissolves like". Thus, a polar solute dissolves in a polar solvent and a non-polar solute dissolves in a non-polar solvent.

Therefore, polar (or) ionic molecules like sugar and sodium chloride dissolve in water molecules, which are polar, while non-polar molecules like naphthalene and anthracene dissolve in solvents like benzene and carbon tetrachloride, which are non-polar.

The solubility of ionic compounds is the result of the strong electrostatic interaction between the ions of the solute and the polar molecules of the solvent.

The solubility of non-polar solutes is the result of similar solute-solute, solute-solvent and solvent-solvent interactions.

When a solid solute is added to a solvent, its concentration in the solution increases. This process is known as dissolution.

On continuous addition of the solute, there will come a state where no more of the solute can be dissolved in the solvent at a given temperature Such a solution, is called a saturated solution.

A state of dynamic equilibrium is reached between the solute particles going into the solution and the solute particles separating out. The concentration of the solute in such a solution is its solubility.

If any more solute is added to a saturated solution, it gets separated out, and process is called precipitation.

A solution in which more solute can be dissolved at a specific temperature is called an unsaturated solution.


Solubility of a solute also depends on temperature:

Heat is required to break the bonds holding the molecules in the solid together. At the same time, heat is given off during the formation of new solute-solvent bonds.

If the heat liberated in the dissolving process is greater than the heat required to break the solid apart, the net dissolving reaction is exothermic in nature.

As per Le-Chatlier's principle, for an exothermic dissolution process, an increase in temperature inhibits the dissolving reaction, since excess heat is already being produced by the reaction.

If the heat given off in the dissolving reaction is less than the heat required to break the solid apart, the net dissolving reaction is endothermic.

As per Le-Chatlier's principle, for an endothermic dissolution reaction, more heat facilitates the dissolving reaction by providing energy to break the bonds in the solid.

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