Solubility: Factors Affecting Solubility

Solubility

Solubility is defined as the greatest amount of a solute that can dissolve in a known quantity of solvent at a given temperature. The degree to which a substance dissolves in a solvent to form a solution is known as its solubility.  The solubility of one fluid (liquid or gas) in another can be complete (completely miscible; for example, methanol and water) or partial (oil and water only partly dissolve).

It can also be described as a substance’s (solute’s) ability to dissolve in a specific solvent. A solute is any substance that can be solid, liquid, or gas, dissolved in a solvent. So, it is the property of a substance that allows it to be entirely or partially combined with another substance, depending on the type of solvent and solute. A solution is composed of a solute and a solvent. The solute is a dissolved material found in minute amounts in a solution. The solvent is the material that is present in greater quantities than the solute and is responsible for dissolving the solute and forming the solution. Some separation processes (absorption, extraction) rely on solubility differences, which are expressed as the distribution coefficient (the ratio of a material’s solubilities in two solvents).

The factors influencing solubility depend on the condition of the solute and are categorized as follows:

  • Gases in Liquids
  • Liquids in Liquids
  • Solids in Liquids

Solubility of gas in liquid

The volume of a gas that may dissolve in a unit volume of liquid to form a saturated solution at ambient temperature or the experimental temperature and under one atmospheric temperature is thus described as its solubility in liquids. Solubility of gas in liquids is the concentration of dissolved gas in the liquid when it is in equilibrium with pure gas above the solution. Effervescent preparations with dissolved carbon dioxide, ammonia water, and hydrochloride gas are examples of gas in a liquid.

Aerosol products that use carbon dioxide or nitrogen as a propellant are also regarded as solutions of gases in liquids. Nitrogen, hydrogen, oxygen, helium, and other gases dissolve slightly in water, but ammonia, sulfur dioxide, hydrogen chloride, and other gases are highly soluble in water. Those gases that chemically react with the liquid solvent are the most soluble.

Factors affecting the solubility of gases

Mass of gases

The level of solubility decreases with increasing gas molecule mass. The solubility of a gas in liquids increases as the molecular mass of the gases decreases.

Pressure

The solubility of gases in liquids increases as pressure rises. The frequency of gas molecule collisions increases as the pressure over the solution rises. This, in turn, makes it easier for the gas particles to combine with the solvent, i.e., the liquid. As a result, when pressure rises, so does the solubility of gases in liquids.

Temperature

The solubility property of a solute can be improved by changing the temperature. In general, water dissolves solutes at 20° C or 100° C. Increasing the temperature will fully dissolve compounds that are sparingly soluble in liquid or solid form. However, when the temperature rises, the solubility of gases in liquids decreases. As the temperature rises, gases become less soluble. When gas molecules dissolve in liquids, they go through a process known as dissolution. During this process, heat is produced.

Solubility of liquid in the liquid

The constituents of an ideal solution are miscible in all proportions.

Under typical conditions, such perfect miscibility is also observed in several true binary systems, such as ethanol and water.

 When partial miscibility occurs under normal conditions, the degree of miscibility is usually temperature dependant.

Factors affecting the solubility of liquid in the liquid

Temperature

Solubility increases with an increase in temperature.

Pressure

Solubility increases with the increase in pressure.

Intermolecular force

It changes depending on the sort of intermolecular forces and bonds present. As a result, like dissolves like, and unlike dissolves difficulty. For example, aromatic hydrocarbons dissolve in each other but not in water.

Solubility of solid in liquid

When a solid solute is given to a solvent, solute particles dissolve in it via the dissolution process. The dissolving process continues until the solution reaches a predetermined maximum concentration. A saturated solution is one in which no additional solute can be dissolved at the same temperature and pressure. An unsaturated solution is one in which more solute can be dissolved at the same temperature.

A substance’s solubility at a given temperature is defined as the quantity of solid that dissolves in 100 g of solvent at that temperature to form a saturated solution. Collisions between solute particles in solution detach some of the particles from the solution. This is known as crystallization. A state of dynamic equilibrium is established between these two processes, at which point the number of solute molecules entering the solution equals the number of particles leaving the solution, resulting in a constant solute concentration in the solution at a given temperature and pressure.

Factors affecting the solubility of solids in liquid

Nature of solute and solvent

A solid dissolves in a liquid (solvent) if the intermolecular interactions of the solute and the solvent are similar. Ionic (or polar) chemicals dissolve more easily in polar solvents such as water and are almost insoluble in non-polar solvents such as benzene, ether, and carbon tetrachloride. Non-polar (covalent or organic) chemicals are soluble in non-polar solvents such as benzene, ether, and carbon tetrachloride but are insoluble in water (polar solvent). Common salt (sodium chloride) and sugar, for example, dissolve easily in water.  Non-polar chemicals naphthalene and anthracene are insoluble in water but readily dissolve in benzene.

Temperature

Temperature effects on solid solubility differ depending on whether the process is endothermic or exothermic. If the solute dissolves through the endothermic process of absorbing heat, the solubility increases as the temperature rises. However, if the solute dissolves with the evolution of heat (exothermic process), solubility decreases as temperature rises.

Pressure

Pressure has a negligible effect on the solubility of solids in liquids. Because solids and liquids are highly incompressible, pressure changes have minimal impact on their solubility.

Physical change

When a substance undergoes a physical change, its composition stays unchanged despite the rearranging of its molecules. It is only a short-term modification.

 It only alters the physical features of the substance, such as shape and size. It requires very little or no energy absorption and does not include the production of energy. Physical change is easily reversed, which means that the original substance can be regained.

Chemical change

A substance’s molecular composition changes completely when it experiences a chemical transformation. As a result, chemical changes result in the production of new compounds. Chemical alters the physical and chemical properties of a substance, as well as its composition. A chemical alteration is irreversible. Absorption and evolution of energy occur during a chemical reaction.

References

  1. https://www.britannica.com/science/solubility-chemistry.
  2. https://byjus.com/chemistry/solubility/.
  3. https://chem.libretexts.org/Courses/University_of_Kentucky/UK%3A_CHE_103_-Chemistry_for_Allied_Health(Soult)/Chapters/Chapter_7%3A_Solids_Liquids_and_Gases/7.7%3A_Solubility.
  4. https://chemed.chem.purdue.edu/genchem/topicreview/bp/ch18/soluble.php.
  5. https://www.excellup.com/class_12/chemistry_12/12-chemistry-solution-solubility.aspx.

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Kabita Sharma

Kabita Sharma, a Central Department of Chemistry graduate, is a young enthusiast interested in exploring nature's intricate chemistry. Her focus areas include organic chemistry, drug design, chemical biology, computational chemistry, and natural products. Her goal is to improve the comprehension of chemistry among a diverse audience through writing.

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