Question

The size of solute should be ____ for better solubility.

Answer 1

The maximum amount of a substance that can be dissolved in a given volume of solvent is called solubility of that solution. When a solution reaches its maximum solubility it is called a saturated solution. If more solute is added to the solution at this point, it will not dissolve into the solution.

Complete answer:
The size of the solute should be larger for better solubility. The larger the size of the molecules of the solute are, the larger will be its molecular weight and their size. It is more difficult for the molecules of the solvent to surround the solute if they consist of bigger molecules. If the particle size is small, then there is effective solvation by the solvent and hence the solubility will be more.
We know that solute getting dissolved is a surface phenomenon. This means that the action takes place only at the surface of each particle. When we break down a molecule of the solute into smaller particles, the total surface area of the solute particles increases. This means the solute will dissolve more rapidly. Thus breaking a solute into smaller pieces increases its surface area and this in turn increases its rate of solvation or solubility.

Note:
Other major factors that affect solubility are the nature of the solute and the solvent, Temperature, Pressure. Some other minor factors are stirring rate, amount of solute that is already added in the solvent. Solubility increases with increase in pressure (for gases), temperature and more stirring. But it decreases with the amount of solute already added and bigger size of solute molecule.