Table of Contents

What is Solubility?Solubility ProductSolubility of Liquids In LiquidsSolubility of Solids In LiquidsSolubility of Gases In LiquidsFactors Affecting Solubility

What is Solubility?

The maximum amount of solute that can dissolve in a known quantity of solvent at a certain temperature is its solubility.

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A solution is a homogeneous mixture of one or more solutes in a solvent. Sugar cubes added to a cup of tea or coffee is a common example of a solution. The property which helps sugar molecules to dissolve is known as solubility. Hence, the term solubility can be defined as a property of a substance (solute) to dissolve in a given solvent. A solute is any substance which can be either solid or liquid or gas dissolved in a solvent.

Solubility Product

The term solubility product is generally applicable for sparingly soluble salts. It is the maximum product of the molar concentration of the ions (raised to their appropriate powers) which are produced due to dissociation of the compound.

At a given temperature the solubility product is constant. Lesser the value of solubility product indicates lower solubility and higher value of solubility product indicates greater solubility.

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On the basis of solubility, the factors affecting solubility vary on the state of the solute:

Liquids In LiquidsSolids In LiquidsGases In Liquids

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Factors Affecting Solubility:

The solubility of a substance depends on the physical and chemical properties of that substance. In addition to this, there are a few conditions which can manipulate it. Temperature, pressure and the type of bond and forces between the particles are few among them.

Temperature:

By changing the temperature we can increase the soluble property of a solute. Generally, water dissolves solutes at 20° C or 100° C. Sparingly soluble solid or liquid substances can be dissolved completely by increasing the temperature. But in the case of gaseous substance, temperature inversely influences solubility i.e. as the temperature increases gases expand and escapes from their solvent.Pressure:Gaseous substances are much influenced than solids and liquids by pressure. When the partial pressure of gas increases, the chance of its solubility is also increased. A soda bottle is an example of where CO2 is bottled under high pressure.

2. Solubility of Solids In Liquids

It has been observed that solid solubility depends on the nature of the solute as well as the solvent. We often see that substances like sugar, common salt (NaCl), etc readily dissolve in water while substances like naphthalene do not dissolve in water. From the various observations and experimental results, it has been seen that only polar solutes tend to dissolve in the polar solvent and non-polar solvents dissolve only non-polar solutes. Hence, the nature of the solvent can be seen as one of the prominent factors affecting solubility. The above observation led to the statement that like dissolves like, that is polar solvents will dissolve polar solutes and non-polar solvents dissolve non-polar solutes.

Now let us understand the process by which a solid dissolves in a solvent. Once a solid solute is added to a solvent, the solute particles dissolve in the solvent and this process is known as dissolution. Solute particles in the solution collide with each other and some of these particles get separated out of the solution, this process is called crystallization.

A state of dynamic equilibrium is established between these two processes and at this point, the number of solute molecules entering the solution becomes equal to the number of particles leaving the solution. As a result, the concentration of the solute in the solution will remain constant at a given temperature and pressure.

A solution in which no more solute can dissolve in the solvent at a given temperature and pressure is said to be a saturated solution as the solution contains the maximum amount of solute. The concentration of solute in such a solution is called its solubility at that temperature and pressure. If more solute can be added to a solution then it is called an unsaturated solution.


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Solubility – Solids in Liquids


Factors Affecting Solubility

Effect of Pressure:

Solid solubility hardly gets affected by changes in pressure. This is due to the fact that solids and liquids are highly incompressible and practically do not get affected by changes in pressure.

3. Solubility of Gases In Liquids

Gas solubility in liquids deals with the concept of gas dissolving in a solvent. Let us first define solubility. For any substance, solubility is the maximum amount of solute that can be dissolved in a given solvent at a particular temperature. Now our concern is gas solubility in liquids. The gas solubility in liquids is greatly affected by temperature and pressure as well as the nature of the solute and the solvent.


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Solubility – Gases in Liquids


There are many gases that readily dissolve in water, while there are gases that do not dissolve in water under normal conditions. Oxygen is only sparingly soluble in water while HCl or ammonia readily dissolves in water.

Factors Affecting Solubility


Frequently Asked Questions – FAQs


Why is solubility test important?


The size and polarity of an unknown compound and the presence of fundamental or acidic functional groups can be inferred by solubility measures. The solubility of a compound in aqueous acid or base requires the compound’s ionisation and, thus, a chemical reaction.


What causes solubility?


Usually, the solubility of a given solute in a given solvent depends on temperature. Solubility tends to equate with rising temperature for several solids dissolved in liquid water. They vibrate faster as water molecules heat up, and are better able to communicate with and split the solution apart.


Does pH affect solubility?


The solubility of the solute can affect the pH of an aqueous solution. If the solution’s pH is such that no net electrical charge is borne by a specific molecule, the solution also has minimal solubility and precipitates out of the solution.


Does temperature affect solubility?


The solubility increases with temperature for certain solids that are dissolved in liquid water. The rise in higher temperature kinetic energy helps the solvent molecules to break apart the solute molecules that are kept together by intermolecular attractions more effectively.

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How does temperature and pressure affect solubility?


In this reaction, an increase in pressure and a rise in temperature contributes to greater solubility. To decrease the partial pressure, an increase in pressure results in more gas particles entering the liquid. The solubility will, therefore, increase.