Dissolution, Factors affecting the rate of dissolution, Solubility & Types of Solubility.

Dissolution and Solubility:

Solution: Solution is the homogenous mixture of solute and solvent.

Generally the largest portion of the solution is called solvent and the smallest portion which is dissolved is the solvent is called solute.

Dissolution: The transfer of molecules or ions from a solid state into solution is known as dissolution.

Factors

Factors affecting the rate of dissolution:

1.       Size of solid particles.

2.       Dispersibility of powdered solid in dissolution medium.

3.       Porosity of solid particles.

4.       Temperature

5.       Nature of dissolution medium.

6.       Molecular structure of solute.

7.       Crystalline form of solid.

8.       Volume of dissolution medium.

9.       pH

Solubility: The solubility of a substance is the maximum amount of that substance which can dissolve in a certain amount of solvent definition

A good solvent is usually based on the 'like dissolves like' principle, that is, a solute dissolves best in a solvent with similar chemical properties. The concept traditionally follows two rules:

1.       Polar solutes dissolve in polar solvents.

2.       Non-polar solutes dissolve in non-polar solvents.

Determination of the solubility of a solid in a liquid

The following points should be observed in all solubility determinations:

1.       The solvent and the solute must be pure.

2.       A saturated solution must be obtained before any solution is removed for analysis.

3.       The method of separating a sample of saturated solution from undissolved solute must be satisfactory.

4.       The method of analysing the solution must be reliable.

5.       Temperature must be adequately controlled.

Types of Solubility:

Description	Approximate weight of solvent (ml) necessary to dissolve 1 g of solute
Very soluble	< 1	less than 1 ml solvent is required to dissolve 1 gm of solute
Freely soluble	Between 1 and 10	Solvent between 1 ml to 10 ml is required to dissolve 1 gm of solute
Soluble	Between 10 and 30	Solvent between 10 ml to 30 ml is required to dissolve 1 gm of solute
Sparingly soluble	Between 30 and 100	Solvent between 30 ml to 100 ml is required to dissolve 1 gm of solute
Slightly soluble	Between 100 and 1000	Solvent between 100 ml to 1000 ml is required to dissolve 1 gm of solute
Very slightly soluble	Between 1000 and 10 000	Solvent between 1000 ml to 10 000 ml is required to dissolve 1 gm of solute
Practically insoluble	> 10 000	Greater  than 10 000 ml solvent is required to dissolve 1 gm of solute