Difference Between Saturated and Supersaturated Solution

Key Difference – Saturated vs Supersaturated Solution
 

Let us first briefly look at the concept of saturation before moving on to a complex analysis of the difference between Saturated and Supersaturated Solution. Solutions are made by dissolving a solute in a solvent. The two chemical properties of “saturation” and “supersaturation” in solvents mainly depend on the solubility of the solute in the solvent. At a given temperature, the solubility of a solute in a particular solvent is a constant (Q).

Q is defined as the ion product of the solute.

Example: Solubility of AgCl in water (Q_AgCl) = [Ag⁺][Cl^–]

Generally, if we keep on adding the solute into the solvent, there is a maximum quantity which we can add dissolve in the solvent. After a certain limit, the solute starts to precipitate in the solvent. It becomes a supersaturated solution after this limit. It is called a saturated solution when we can dissolve the solute with no formation of a precipitate.

The key difference between Saturation and Supersaturation is that, Saturation is the state  at which a solution of a substance can dissolve no more of that substance, and additional amounts of it will appear as a separate phase while supersaturation is a state of a solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances.

What is a Saturated Solution?

There is a very limited number of compounds which are infinitely soluble in a solvent; which means, we can mix the solute in the solvent in any proportion to dissolve without forming a precipitate. However, most of the solutes are not infinitely insoluble; they form a precipitate if you add more solute into the solvent.

Saturated solutions contain the maximum number of solute molecules it can dissolve with no precipitation.

What is a Supersaturated Solution?

Supersaturated solutions are formed if you add additional solute to the saturated solution. In other words, it is the condition in a saturated solution, when you add some additional quantity of solute into the solution. Then it will start to form a precipitate in the solution because the solvent has exceeded the maximum quantity of solute molecules it can dissolve. If you raise the temperature of the solvent, you can make a saturated solution by dissolving the solute molecules.

What is the difference between Saturated and Supersaturated solution?

Definition of Saturated and Supersaturated Solution

Saturated Solution: At a particular temperature, a solution is said to be a saturated solution, if it contains as much as solute molecules which the solvent can hold.

Supersaturated Solution: At a particular temperature a solution is said to be a supersaturated solution if it contains more solute molecules it can dissolve.

Chemical Explanation

For saturated solutions; Q = K_sp (No precipitation)

For supersaturated solutions; Q > K_sp (Precipitate will form)

Where;

Q = solubility (reaction quotient)

K _sp= Solubility product (mathematical product of dissolved ion concentrations raised to the power of their stoichiometric coefficients)

Example: Consider dissolving Silver Chloride (AgCl) in water.

AgCl – Solute   and     Water – Solvent

AgCl has dissolved in water                           A large quantity of AgCl has dissolved in water.

The solution is clear                                        The precipitate is clearly visible

Q= [Ag⁺][Cl^–] = K_sp                                          Q= [Ag⁺][Cl^–] > K_sp

Where,

[Ag⁺]= Concentration of Ag⁺ in water

[Cl^–] = Concentration of Cl^– in water

For AgCl, K_sp = 1.8 ×10^–10  mol²dm^-6 

How can we make saturated and supersaturated solutions?

Both saturated and supersaturated solutions are formed when you keep on adding a particular solute into a solvent. At a given temperature, first, it forms an unsaturated solution and then, a saturated solution and finally the supersaturated solution.

Example: Dissolving salt in water

Unsaturated Solution: Less amount of salt in water, clear solution, no precipitation.

Saturated Solution: The maximum amount of salt is dissolved in water, Colour of the solution slightly changes, but no precipitation.

Supersaturated Solution: More salt is dissolved in water, Cloudy solution, precipitation is visible.

 

Image Courtesy:

“Rock-Candy-Sticks” by Evan-Amos – Own work. (CC BY-SA 3.0) via Commons