It is the maximum extent of solute that can dissolve in a certain amount of solvent at certain conditions i.e. temperature and pressure at equilibrium. Example- in case of fluids (gas or liquid) solubility, if one liquid is solubilized into another it is referred to as miscible like methanol and water with each other. Another case is water and oil which are not solubilized into each other referred to as immiscible.

There is a concept that ‘like dissolves like’ as aromatic hydrocarbons they are not miscible with water but are miscible with one another. Techniques of separation such as extraction i.e. separating the different constituents from the material it relies on differences in solubilities of various constituents in different solvents known as distribution coefficient.

Another example where the solute is solid like salt in water, now while dissolving the salt in water a point comes when no more salt can be incorporated known as saturation point and this is the point of maximum solubility. If solute incorporated is less than saturation point, it is referred to as unsaturation. If the solute concentration is comparatively very less than solvent then the solution is said to be dilute and if the solute is in high amount than solvent, the solution is known as concentrated.

Solubilities ranges widely from completely or highly soluble (i.e. ethanol in water) to poorly soluble (i.e. silver chloride in water).

The solubility of gases in liquids is greatly affected by the temperature and pressure. When temperature increases the solubility of gases decrease. This effects water ecosystem, as when industrial hot waters are discharged into river, lake or streams, it leads to the death of fishes on large scale.

The solubility of gas is also affected by pressure as the pressure increases the solubility of gases also increases in solution. Its example is fizzy carbonated drink, which is sealed with high pressure saturated with carbon dioxide gas. When the sealed bottle is opened hiss sound of gas bubbles is heard because carbon dioxide gas is leaving the solution in form of small gas bubbles which can be seen. This has been explained by Henry’s law.

The solubility of liquids in liquids is based on the statement ‘like dissolves like’. Water is polar in nature hence liquids having polar nature they dissolve in water due to the formation of hydrogen bonds. Similarly, non-polar liquids are miscible with each other because there is not any difference in intermolecular attractions. The water and oil they form layers as they do not mix together as water molecules have a strong attraction with each other so they squeeze out the non-polar liquid. Other case is solubility of bromine in water which is partially soluble with other.

The solubility of the solid substance in the liquid is expressed as grams of solute per liter of solvent. As the temperature increases the solubility increases and it may lead to the formation of supersaturated solutions.

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