What Is a Supersaturated Solution?

A solution is defined as a homogeneous mixture of either two or more pure substances on a molecular level, whose composition may vary within particular limits. A solution that has two components (otherwise substances) is called the solute and the solvent.

Whenever two or more compounds are mixed it will result in the formation of the solution. Based on solutions and the amount of solvent dissolved in the solution. It can be categorized into three different types. They are namely unsaturated solution, saturated solution, and Supersaturated Solution. Unsaturated solutions are the ones where you can easily dissolve more solute in them, that is it is not saturated. Any solution in which no more solute can be added is known as the saturated solution and the solution which has more solute than the saturated solution at a particular time and pressure is known as the Supersaturated Solution.

Here you are going to get s brief knowledge about Supersaturated Solutions just has a look into it. 

Earlier studies of this phenomenon were conducted by using the compound of sodium sulfate commonly called the glauber's salt. This is because the solubility of this salt in water decreases with an increase in temperature. A Supersaturated Solution as we said earlier can be prepared by adding more and more solute to the already saturated solution and this can be possible by changing the temperature of the solution and then adding more and more solute until it stops dissolving anymore. 

What is a Supersaturated Solution?

A Supersaturated Solution definition is given as the one, which contains more dissolved solute than needed for preparing a saturated solution and is prepared by heating a saturated solution, adding excess solute, and then by gently cooling it. And, the excess dissolved solute will crystallize by seeding the Supersaturated Solution with fewer solute crystals.

Many times students tend to get confused between saturated and Supersaturated Solutions. So the main difference is that if you look for a saturated solution, it involves the Dissolving of the solutes continuously until it is about Dissolving of more solute in it, that is no more solute can dissolve.

While talking about Supersaturated Solution it is the solution that firstly has more solute as compared to the saturated solution and also the solute particles are large in number as compared to the one in the saturated solution.  The saturated solution has less solute as compared to the Supersaturated Solution. Let's understand this topic more by using the examples given below.

For example, the pan boiling object is the production of a fine even crop of sugar crystals. A major condition for the attainment of this end is given as the maintenance of control over the crystallization rate during the growth. Generally, a crystal surface, which is maintained in a solution will only grow when the concentration of the solution is maintained at a greater level compared to the saturation concentration. Such a kind of solution is said to be supersaturated.

Supersaturation in Phase Change (Crystallization and Condensation)

• Physical and chemical processes in the vapor melt or the solution phase of each system occur through the formation of three-dimensional nuclei of a new phase and take place only when the medium gets supersaturated.

• The production of the nuclei is associated with a change in the system’s free energy. In the homogeneous system, the nuclei of the new phase are not produced as soon as the system becomes supersaturated though thermodynamically, such a situation becomes possible.

• The system is known to be in a metastable equilibrium state, and it can remain in the same state without attaining the least or minimum free energy corresponding to the equilibrium state.

• In other terms, in such cases, the nucleation of new phase sets in after some period, where the value depends on such factors as the pressure and temperature of the system, the presence of chemical phases varies from the increased supersaturation level, and nucleating phase facilitates the nucleation process of the new phase.

• However, there is a supersaturation level always when a new phase instantaneously nucleates. That is called the new phase precipitates.

• This type of supersaturation level corresponds to the upper limit of the metastable equilibrium state and defines the metastable width.

Applications of Supersaturated Solution

When a solid solute dissolved in a liquid solvent is saturated, it is in thermodynamic equilibrium. For the crystallization to take place, the system state must be shifted to the nonequilibrium state, where the concentration of the solute present in the solution exceeds its equilibrium concentration at given solution conditions. And, the solutions present in the nonequilibrium state are known to be supersaturated. The easiest method to create a Supersaturated Solution is achieved by cooling.

Initially, a solution can be prepared at point A. If the prepared solution is cooled, it will be saturated when it intersects the line of saturation. If it is cooled previously, the saturation line to point B will be supersaturated. Only because this solution is supersaturated, but, does not mean that it will crystallize immediately. Supersaturated Solutions are said to be metastable. It means there is a free energy barrier that should be overcome for the phase transition, which is to be overcome.

The most common and simplest method of making a Supersaturated Solution is given by cooling. However, this is not the only available method to be used. There are several other methods such as temperature change, change in pH, solvent evaporation, chemical reaction & alteration in solvent composition.

Supersaturated Solution Examples

It is very easy to understand the Supersaturated Solution, and you can easily tell whether the solution is saturated, unsaturated or supersaturated. This can be done by adding just a small amount of solute. If the solution is unsaturated the solute will easily dissolve. If it is saturated the solute is not going to dissolve and if the solution is supersaturated then there will be the immediate formation of crystals around the solute that you have recently added.

A Supersaturated Solution is a result of a solution having concentration more at an increased temperature and it is cooled down to a particular temperature,  at this temperature the solution will be known as a Supersaturated Solution.

Let us look at the saturated solution examples.

The Supersaturated Solution holds more dissolved substances compared to a saturated solution. For example, 40g NaCl is present in 100ml H₂O. The additional 4.0g NaCl remains to be undissolved.

Way to achieve a Supersaturated Solution?

To achieve a Supersaturated Solution you need to add heat, but remember a small amount of heat will not make any difference. You need to add a large amount of heat, like for water you have to heat it to its boiling point. When the solution such as water is heated up to its boiling point there will be more space between the molecules as the molecules can move more freely. If the space between the molecules increases then there will be more space for the solute particles to get adjusted with the water molecules and a Supersaturated Solution will be formed.

Solved Examples

1. Give the Mass Percent of Sodium Hydroxide Present in a Solution, Made by Dissolving 8.00g NaOH in 50.0g H₂O?

Solution

It is given that 8.00g NaOH

50.0gms H₂O

Solving for mass

= 8.00g NaOH/8.00gms NaOH + 50.0g H₂O

= 13.8% NaOH solution.

2. Will a Solution Prepared by Adding 2.5g of CuSO₄ to 10gms of H₂O be Saturated for the Unsaturated Solution at 20^oC?

Solution

First, we need to know the CuSO₄ solution at 20^oC. From the above-given figure, we can see that the CuSO₄ solubility at 20^oC is about 21gms per 100g of H₂O. This particular amount is equivalent to 2.1gms of CuSO₄ per 10gms of H₂O. Since 2.5gms per 10gms of H₂O is greater than the 2.1gms per 10gms of H₂O, the solution will become saturated, and 0.4gms of CuSO₄ will be maintained.

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