Solubility

You know quite a bit about solutions. Your favorite lemonade is a solution! Isn’t it? However, do you know what solubility is? What is the solubility of a lemonade? Let us look at the concept of solubility in this chapter. We will look at the solubility of different solutions. Let’s begin.

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What is Solubility?

Solubility is the maximum amount of solute which dissolves in a specified amount of solvent at a specific temperature. It is the interaction between particles of the solute and the solvent.

Therefore, it depends on the nature of the solute and the solvent. The solubility of solids in liquids is independent of pressure. We will now look at the solubility of solids in liquids.

Browse more Topics under Solutions

• Abnormal Molar Masses
• Colligative Properties and determination of Molar Mass
• Expressing Concentration of Solutions
• Ideal and Non-ideal Solutions
• Osmosis and Osmotic Pressure
• Types of Solutions
• Vapour Pressure of Liquid Solutions

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The Solubility of Solids in Liquids

Two factors determine the solubility of solids in liquids,

• Nature of the solute and solvent
• The temperature

1) Nature of the Solute and Solvent

In general “like dissolves like”. Thus, a polar solute dissolves in a polar solvent, and a non-polar solute dissolves in a non-polar solvent. Therefore, polar (or) ionic molecules like sugar and sodium chloride dissolve in water molecules as these are polar. On the other hand, non-polar molecules like naphthalene and anthracene dissolve in solvents like benzene and carbon tetrachloride as these are non-polar.

The solubility of ionic compounds is the result of the strong electrostatic interaction between the ions of the solute and the polar molecules of the solvent. On the other hand, the solubility of non-polar solutes is the result of similar solute-solute, solute-solvent, and solvent-solvent interactions.

When there is the addition of solid solute to a solvent, its concentration in the solution increases. This process is known as dissolution.  On continuous addition of the solute, there will come a state where no more solute can dissolve in the solvent at a given temperature. Such a solution is known as a saturated solution.

A state of dynamic equilibrium reaches between the solute particles going into the solution and the solute particles separating out. The concentration of the solute in such a solution is its solubility. If any more solute is added to a saturated solution, it will separate out. This is the process of precipitation. A solution in which more solute can be dissolved at a specific temperature is an unsaturated solution.

2) Temperature

We require heat to break the bonds holding the molecules in the solid together. At the same time, the formation of new solute-solvent bonds gives off heat. If the heat liberated in the dissolving process is higher than the heat required to break the solid apart, the net dissolving reaction is exothermic.

The Solubility of a Gas in Liquids

If you thought only solids dissolve in liquids, you are wrong! Even gases dissolve in liquids. One common example of this would be the cold drinks that you enjoy or the aerated drinks. They have carbon dioxide dissolved in them.

Solved Example for You

Q: Explain the Le-Chatelier’s principle.

Solution: As per Le-Chatlier’s principle, for an exothermic dissolution process, an increase in temperature inhibits the dissolving reaction. This is because the reaction already produces the excess heat. If the heat given off in the dissolving reaction is less than the heat we require to break the solid apart, the net dissolving reaction is endothermic.

As per Le-Chatlier’s principle, for an endothermic dissolution reaction, more heat facilitates the dissolving reaction by providing energy to break the bonds in the solid.