A Short Note on Solute-solid Equilibrium

The solute-solid equilibrium is a type of equilibrium. Here, equilibrium is achieved when the solid does not get dissolved since the solution is saturated. The solute concentration in a solution that is saturated is called solubility. This equilibrium is reached when the solid state of a compound does not go through any changes and is in chemical equilibrium with the solution it is in. The Solute-Solid Equilibrium is a demonstrative example of thermal equilibrium. The solubility depends on the temperature of the compound or the solution. The units are molar or mass per unit volume. The article has discussed the concepts of a common ion effect, solution equilibria, and solubility equilibrium at length. 

Solute-Solid Equilibrium

There have been many academic publications on the importance of solid-solute equilibrium. Academically, it is known as SSAS (Solid-Solution-Aqueous solution). Thermodynamic models play a significant role in industries and environment-oriented applications. So, incorporating SSAS in the thermodynamic models utilised here is important. The study of solute-solid equilibrium was only restricted to solids, but as can be seen naturally, most minerals found in nature and solid electrolytes too are homogenous mixtures of solid or solid solutions. The effect is studied by electrolytes and salts. It is widely observed in weak electrolytes like salts. Related to this is the concept of a common ion effect. The dilution happens until solubility equilibrium is achieved. A Common ion effect is the result of Le Chatelier’s principle. 

Common Ion Effect

According to Le Chatelier, any changes that are introduced to the status quo, an opposing reaction is prompted. This happens after a system that has been in equilibrium for a while has changed in pressure, temperature, and volume. The system shifts to a new type of equilibrium that counteracts the original change. So, following this, A common ion effect implies the salt or weak electrolyte to which another chemical was added shares one ion in common. Conversely, the uncommon ion effect happens when the total concentration of ions increases and increases salt’s solubility. An alternate equilibrium takes place and that causes less precipitation. A Common ion effect also demonstrates that adding even one ion of a salt results in larger precipitation of salt that dilutes the ions of salts.

Solution Equilibria

The solubility equilibrium and the common ion effect can be witnessed in the example of hydrogen sulphide in hydrochloric acid. Hydrogen sulphide is a weak electrolyte. In the aqueous solution of hydrogen sulphide, there is an equilibrium between unionized ions and molecules in the form of H+ and HS-. So, when Hydrochloric acid is added to it then,

HCl⇋ H+ + Cl-

The common ion is H+. The solubility product constant is a major element of solubility equilibrium.

Solubility Equilibrium

Solubility equilibrium reaches when a chemical compound remains unchanged and attains equilibrium with its solution. It is expressed as Ksp = [A+ ]a [B- ]b where, A+ is a cation, B- is an anion, a and b are relative concentrations and Ksp denotes solubility product constant. 

Conclusion

Solute-Solid Equilibrium is therefore a part of dynamic equilibrium. It exists when a compound as the solid is in chemical equilibrium with its solution. There are no changes or a chemical reaction taking place. The solubility does depend on the temperature and functions akin to an equilibrium constant. This has a lot of uses in the chemical industries, especially in pharmaceuticals.