Supersaturated Solution - Definition, Examples, Applications, FAQs

What is a Supersaturated Solution?

A supersaturated solution definition in chemistry is a solution containing more than the maximum amount of solute that can dissolve in solvent at a particular given temperature. A supersaturated solution possesses an unstable state; it could be made stable by separating the excess amount of solute dissolved in the solvent.

Examples of Supersaturated Solution

A supersaturated solution contains more solute than can normally dissolve in a solvent at a given temperature. Such solutions are unstable, and excess solute may crystallize out when disturbed.

Here Are 10 Examples of supersaturated solutions

1. Supersaturated Sugar Solution

Prepared by dissolving excess sugar in hot water and then cooling it carefully.

2. Rock Candy Solution

A supersaturated sugar solution is used for growing sugar crystals (rock candy).

3. Supersaturated Sodium Acetate Solution

Used in reusable hand warmers; crystallises instantly when triggered.

4. Supersaturated Sodium Thiosulfate Solution

Commonly used in laboratory crystallisation experiments.

5. Supersaturated Potassium Nitrate (KNO₃) Solution

Formed by dissolving excess KNO₃ in hot water and cooling slowly.

6. Supersaturated Copper Sulphate (CuSO₄) Solution

Used to grow large blue copper sulphate crystals.

7. Supersaturated Alum Solution

Prepared for crystal-growing experiments in schools and laboratories.

8. Supersaturated Epsom Salt ($\left(\mathrm{MgSO}_4 \cdot 7 \mathrm{H}_2 \mathrm{O}\right)$) Solution

Obtained by dissolving excess Epsom salt in hot water.

9. Supersaturated Borax Solution

Used for making borax crystals in chemistry demonstrations.

10. Carbonated Soft Drinks (Under Pressure)

Contain carbon dioxide dissolved in water at concentrations higher than normal due to high pressure; when opened, the solution releases excess CO₂.

Supersaturation in Phase Change (Supersaturation Crystallisation and Condensation)

• In each system, the physical and chemical processes of the vapour melt or the solution phase occur by the formation of three-dimensional nuclei of a new phase and take place only during the supersaturated medium.
• The nuclei’s production is associated with a change in the free energy of the system. In the case of a homogeneous system, the new phase of the nuclei is not produced as soon as the system becomes supersaturated, though thermodynamically, such a situation becomes possible.
• The system is found 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 words, in such cases, the nucleation of a new phase sets in after a time period, where the value depends on factors such as the pressure and temperature of the system, the presence of chemical phases varies with the increasing supersaturation level, and nucleating phase facilitates the nucleation process of the new phase.
• However, there is always a level of supersaturation when the new phase is instantaneously nucleated. It is referred to as the new phase precipitates.
• Such a supersaturation level signifies the upper limit of the metastable equilibrium state and describes the metastable width.

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Applications of Supersaturated Solution

• Supersaturation have practical applications in the field of pharmaceuticals. By preparing a supersaturated solution of a particular drug, it can be ingested in liquid form. The precipitation can be prevented by adding precipitation inhibitors. Drugs in such states are termed "supersaturating drug delivery services," or "SDDS." Oral consumption of a drug in this form is easy and helps in the measurement of very precise dosages.
• Marine ecologists use supersaturated solutions’ identification as a tool for the study of the activity of organisms and populations.
• Supersaturation is an important factor in the design of steam turbines.
• The study of supersaturation is also important for atmospheric studies. Actually, supersaturation of water is very common in the upper troposphere. This can be found using satellite data from the Atmospheric Infrared Sounder.

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Some Solved Examples

Question 1: A beaker contains a solution of the substance ‘A’. Precipitation of substance ‘A’ takes place when a small amount of ‘A’ is added to the solution. The solution is _________.

1) Saturated

2) (correct) Supersaturated

3) Unsaturated

4) Concentrated

Solution:

Saturated, unsaturated, and supersaturated are terms used to describe the amount of solute that can be dissolved in a solvent at a given temperature:

Saturated
A solution that contains the maximum amount of solute that can dissolve at a given temperature. If more solute is added, it will not dissolve and will settle at the bottom of the container as an undissolved solid.

Unsaturated
A solution that contains less than the maximum amount of solute that can dissolve at a given temperature. More solute can be dissolved in an unsaturated solution.

Supersaturated
A solution that contains more solute than the maximum amount that can dissolve at a given temperature. Supersaturated solutions are unstable and the excess solute will usually crystallize, especially if disturbed.

Adding a small amount of solute to an already saturated solution will make the solution supersaturated and will lead to the precipitation of the solute.

Hence, the answer is option (2).

Question 2: On dissolving sugar in water at room temperature solution feels cool to the touch. Under which of the following cases dissolution of sugar be most rapid?

1) Sugar crystals in cold water.

2) Sugar crystals in hot water.

3) Powdered sugar in cold water.

4) (correct) Powdered sugar in hot water.

Solution:

The solution is a homogeneous mixture of two or more chemically non-reacting substances whose composition can be varied within certain limits. A solution that contains only two components is called a binary solution. The component that has the same physical state as the solution is the solvent. In case both the components have the same physical state, then the component that is present in a larger amount is called the solvent, and the other present in a smaller amount is called the solute.

The process by which a solvent and a solute form a solution is called dissolution. When you enjoy salad dressing made with oil and water, it has to be shaken to mix the two. When this occurs, you are eating a (short-lived) dissolution on your salad.

Dissolution is an endothermic process, which is why the solution is cool to the touch. Also, powdered sugars have a higher surface area than sugar crystals, which further promotes dissolution.

Hence, the answer is option (4).

Question 3: Select the correct statement out of the following regarding a binary solution

1) A component that is present in excess is a solute

2) (correct) Component that is present in excess is solvent

3) In a solution, the physical state of the solute is retained.

4) In a solution, the physical state of the solvent is not retained.

Solution:

In a solution, the species that is present in the same state as the solution is the solvent. In case both species are in the same physical state, then the species present in excess is the solvent.

Hence, the correct answer is option (2).

Question 4: A supersaturated solution of sodium acetate is disturbed by adding a small crystal of sodium acetate. Which of the following observations is most likely?

A. The solubility of sodium acetate increases.
B. Excess sodium acetate crystallises out rapidly.
C. Water evaporates instantly.
D. The solution becomes unsaturated.

Solution:

A supersaturated solution is metastable and contains more dissolved solute than it can normally hold at that temperature. When a seed crystal is added, it acts as a nucleation centre, causing the excess dissolved solute to crystallise rapidly. This phenomenon is observed in sodium acetate hand warmers.

Hence, the correct answer is option (B).

Question 5: At 30°C, the solubility of KNO₃ in water is 45 g per 100 g of water. A solution is prepared by dissolving 60 g of KNO₃ in 100 g of water at a higher temperature and then cooled carefully to 30°C without crystallisation.

Which of the following is correct?

A. The solution is unsaturated.
B. The solution is saturated.
C. The solution is supersaturated.
D. KNO₃ cannot remain dissolved.

Solution:

At $30^{\circ} \mathrm{C}$,

$\text { Solubility of } \mathrm{KNO}_3=45 \mathrm{~g} / 100 \mathrm{~g} \mathrm{H}_2 \mathrm{O}$
Amount dissolved:

$60 g / 100 g \mathrm{H}_2 \mathrm{O}$
Since

$60>45$

The solution contains more solute than allowed by its equilibrium solubility at $30^{\circ} \mathrm{C}$.

Hence, it is a supersaturated solution.

Hence, the correct answer is option (C)

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