Solubility

Solubility is the ability that most substances require. The degree of solubility may range from highly soluble or poorly soluble in an aqueous solution. The more the quantity of solute dissolves in the solvent, the higher its solubility. The extent of the solubility of a substance is calculated by the concentration of solute that dissolves in a specific solvent, and no more solute can be dissolved.

Solubility

Solubility is a relative ability of a solid substance to dissolve in an aqueous solution. Under standard conditions and temperature, the greatest amount of solute that dissolves in a known quantity of solvent refers to solubility. When the concentration of solute and solvent reaches the same point, then the solution is at equilibrium, or else it’s called a saturated solution.

The solubility of a substance depends on the composition of the solute, solvent and also the pH of the substances involved. The solubility concept is not applicable for the irreversible chemical reactions between two substances.

Factors affecting Solubility 

• Temperature- For most solutes, the solubility of a substance increases as the temperature increases, but in the case of gases, they become less soluble in water when the temperature increases but become more soluble in organic solvents.
• pH– There is little effect of pH on the non-ionisable substances, and solubility can be increased by changing specific dipole moments.
• Pressure- For the majority of the solid and liquid solutes, the solubility does not affect to that extent, but for gases, Henry’s Law is applicable. It states that the solubility of the gas is directly proportional to the pressure of the gas.
• Chemical Composition- The solubility is dependent on the nature of the solute and solvent used. The presence of other chemicals or compounds can also affect solubility.
• Particle Size- The less the particle size, the more the solubility of a substance in the solvent as there is an increase in the surface area. If the particle size decreases beyond the limit, then the solubility decreases as they will form agglomerates.
• Crystal Structure- The amorphous form of the compound is more soluble than the crystalline form.
• Molecular Structure- The change in the molecular structure of any compound distinctly affects its solubility. For example, the introduction of the hydrophilic group into a hydrophobic compound will increase the solubility. Introduction of benzene into phenol. 

Solute 

The solute is a substance dissolved in another substance that is present in a lesser amount. The amount of solute dissolved in the solvent is the concentration of solute. It can be solid, liquid or gas. Example- salt, sugar

Features of a solute

1) A solute cannot be seen by the naked eye in the solution

2) A solution is a homogenous mixture of two or more components. 

3) A solution is stable.

4) It is only made up of one phase.

5) The solute cannot be separated by filtration or any other mechanical method.

6) A ray of light passed cannot be scattered by the solution.

7) The boiling point of the solute is higher than the solvent.

Solvent

The solvent is the one in greater amount and in which the solute is dissolved. It acts as a medium of dissolving. The solvent is mostly liquid, but rarely it can be solid and gas. Water is a good solvent for polar molecules and is most widely used. Solvents are mostly used in nail polish removers, paints, beverages, inks, etc.

Feature of Solvent-

1. The solvent must be good at solubilising the target compound.
2. The solvent used for extraction purposes must have volatility.
3. The solvent must be less toxic and safe to use.
4. There should be poor solubility of the impurities and other unnecessary compounds.
5. It must be non-flammable.

Conclusion–

Solubility is a fundamental concept in chemistry. All the practical applications in our day-to-day life require the characteristic of solubility in the compounds. According to the thermodynamic cycle, it is said that the stronger the bond between solute and solvent, the greater the chance of forming a solution. The strength of the solute-solvent interaction is dependent on the structure of both of them. We can conclude that the only solute with some similar properties to the solvents can be dissolved properly. Water is the most commonly used solvent.

A substance’s solubility is determined by the solvent employed. The range of solubility varies widely, but the poorly soluble substances are called ‘insoluble’. Solubility plays an important role during the separation of mixtures.