WHAT IS A DILUTE SOLUTION? FACTORS AND EXAMPLES - CHEMISTRY - 2025

A dilute or unsaturated solution is a chemical solution that has not reached the maximum concentration of solute dissolved in a solvent. The additional solute will dissolve when added to a dilute solution and will not appear in the aqueous phase.

From a physico-chemical point of view, an unsaturated solution is considered a state of dynamic equilibrium where the rates at which the solvent dissolves the solute are greater than the rate of recrystallization.

An example of a dilute solution is illustrated in Figure 1. In Figures 1.1, 1.2, and 1.3, there is a constant volume of water in the beaker.

In figure 1.1 the process begins where the solute begins to dissolve, represented by the red arrows. In this case, you see two phases, a liquid and a solid.

Figure 1: example of unsaturated solution.

In Figure 1.2, much of the solid has dissolved, but not completely due to the recrystallization process, represented by the blue arrows.

In this case, the red arrows are larger than the blue arrows, which means that the dilution rate is greater than the recrystallization rate. At this point you have an unsaturated solution.

Thus, we can say that a dilute solution can dissolve more solute in it until it reaches the saturation point. At the saturation point, no more solute will dissolve in the solvent and such a solution is called a saturated solution.

In this way solutions are initially unsaturated in nature and eventually become saturated solutions by adding solute to it.

What is a dilute solution?

A dilute solution is that unsaturated, saturated, or supersaturated solution to which more solvent is added. The result is an unsaturated solution of lower concentration.

Dilutions are a common process in a chemical laboratory. In general, you work with dilute solutions that are made from stock solutions that are those that are purchased directly from a particular merchant.

To make the dilutions, the formula C ₁ V ₁ = C ₂ V _{2 is used} where C is the concentration of the solution, generally in terms of molarity or normality. V is the volume of the solution in ml and terms 1 and 2 correspond to the concentrated and diluted solutions respectively.

Factors Affecting Solubility

The amount of solute that can be dissolved in a solvent will depend on different factors, the most important of which are:

1- Temperature

Solubility increases with temperature. For example, more salt can be dissolved in hot water than in cold water.

However there may be exceptions, for example, the solubility of gases in water decreases with increasing temperature.

In this case, the solute molecules receive kinetic energy as they heat up, which facilitates their escape.

2- Pressure

Increased pressure can force solute dissolution. This is commonly used to dissolve gases in liquids.

3- Chemical composition

The nature of the solute and solvent and the presence of other chemicals in the solution affect the solubility.

For example, more sugar can be dissolved in water than salt in water. In this case, the sugar is said to be more soluble.

Ethanol and water are completely soluble with each other. In this particular case, the solvent will be the compound that is found in greater quantity.

4- Mechanical factors

In contrast to the dissolution rate, which depends mainly on temperature, the recrystallization rate depends on the solute concentration at the surface of the crystal lattice, which is favored when a solution is immobile.

Therefore, agitation of the solution prevents this accumulation, maximizing dissolution.

Saturation and solubility curves

The solubility curves are a graphical database where the amount of solute that dissolves in a quantity of solvent is compared, at a given temperature.

Solubility curves are commonly plotted for an amount of solute, either solid or gas, in 100 grams of water. Saturation curves for various solutes in water are illustrated in Figure 2.

Figure 2: saturation curves. On the abscissa the degrees of temperature are represented, while on the ordinate, the grams of solute in 100 grams of water.

The curve indicates the saturation point at a given temperature. The area under the curve indicates that you have an unsaturated solution and therefore more solute can be added. In the area above the curve there is a supersaturated solution.

Taking sodium chloride (NaCl) as an example, at 25 degrees centigrade approximately 35 grams of NaCl can be dissolved in 100 grams of water to obtain a saturated solution.

Examples of dilute solutions

Unsaturated solutions can be found on a day-to-day basis, it is not necessary to be in a chemical laboratory.

The solvent does not necessarily have to be water. Below are everyday examples of dilute solutions:

• Adding a tablespoon of sugar to a cup of hot coffee produces an unsaturated sugar solution.
• Vinegar is a dilute solution of acetic acid in water.
• Fog is an unsaturated (but close to saturated) solution of water vapor in the air.
• 0.01 M HCl is an unsaturated solution of hydrochloric acid in water.
• Rubbing alcohol is a dilute solution of isopropyl alcohol in water.
• The soup is an unsaturated solution of water and sodium chloride.
• Alcoholic beverages are dilute solutions of ethanol and water. Usually the percentage of alcohol that they have is shown.

References

1. Anne Marie Helmenstine, P. (2016, July 7). Saturated Solution Definition and Examples. Recovered from about.com.
2. Cambrige University. (sf). Solubility curves. Recovered from dynamicscience.com.au.
3. Examples of Saturated Solution. (sf). Recovered from examples.yourdcitionary.com.
4. J., S. (2014, June 4). Saturated and Supersaturated Solutions. Recovered from socratic.org.
5. James, N. (nd). Saturated Solution: Definition & Examples. Recovered from study.com.
6. M., B. (2014, October 14). Saturated and Supersaturated Solutions. Recovered from socratic.org.
7. Solubility Curves. (sf). Recovered from kentchemistry.com.
8. Tipes of saturation. (2014, June 26). Recovered from chem.libretexts.org.