What factors affect solubility?

Solubility is affected by 4 factors – temperature, pressure, polarity, and molecular size. 

• Effect of temperature on solubility 

Solubility increases with temperature for most solids dissolved in liquid water. This is because higher temperatures increase the vibration or kinetic energy of the solute molecules. Solute molecules are held together by intermolecular attractions. The increased kinetic energy weakens the intermolecular attractions, making it easier for the solvent molecules to break up the solute molecules, causing them to dissolve more readily. Temperature affects gas solubility differently. Solubility of a gas in water decreases with increasing temperature while solubility of a gas in an organic solvent tends to increase with increasing temperature.

• Effect of pressure on solubility 

Solubility of a gas in a solvent increases with increasing temperature, although the increase in solubility based on pressure is not the same for all gasses. The effect of pressure on the solubility of condensed phases - solids and liquids - is negligible. 

• Effect of polarity on solubility 

In most cases, polar solute will dissolve in a polar solvent while a nonpolar solute will dissolve a nonpolar solvent. Polar solutes will not dissolve in a nonpolar solvent and vice versa. The reason fat does not dissolve in water is because fats are nonpolar and water is polar. 

• Effect of molecular size on solubility

Solubility decreases as the molecular size increases. The larger the size of molecules in a solute, the more difficult it is for solvent molecules to wrap around them in order to dissolve them. On the other hand, solvent molecules wrap around molecules of smaller size more easily, increasing the solubility of the substance. In general, under the same temperature and pressure conditions, solutes with smaller particles are more soluble than solutes with larger particles. Changing the temperature and pressure can change the solubility of the substance.