A Saturated solution Is a chemical solution containing the maximum concentration of solute dissolved in a solvent.
Additional solute will not dissolve in a saturated solution and will appear in a different phase, either a precipitate if it is a solid in liquid or an effervescence if it is a gas in a liquid (Anne Marie Helmenstine, 2016).
In other words, from a chemical physical point of view, a saturated solution is considered a state of dynamic equilibrium where the rates at which the solvent dissolves the solute and the rate of recrystallization are equal (J. , 2014).
An example of a saturated solution is illustrated in Figure 1. In Figure 1.1, 1.2 and 1.3 there is a constant volume of water in the beaker. In Figure 1.1 the saturation process begins, where the solute begins to dissolve, represented by the red arrows.
In Figure 1.2, much of the solid has dissolved, but not completely due to the recrystallization process, represented by the blue arrows.
In Figure 1.3, only a small amount of solute remains undissolved. In this case, the rate of recrystallization is greater than the rate of dissolution. (Types of saturation, 2014)
The point of maximum concentration of a solute in a solvent is known as a saturation point.
Factors Affecting Saturation
The amount of solute that can be dissolved in a solvent will depend on different factors, among them the most important 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 the gases in water decreases with increasing temperature. In this case, solute molecules receive kinetic energy upon heating which facilitates their escape.
2 - Pressure
The increase in pressure can force solute dissolution. This is commonly used to dissolve gases into liquids.
3 - Chemical composition
The nature of the solute and the solvent and the presence of other chemical compounds in the solution affect the solubility. For example, a greater amount of sugar can be dissolved in water, than salt in water. In this case it is said that sugar is more soluble.
Ethanol in water are completely soluble with one another. In this particular case, the solvent will be the compound that is in the greatest amount.
4 - Mechanical Factors
In contrast to the rate of dissolution, which depends mainly on temperature, the rate of recrystallization depends on the concentration of solute on the surface of the crystalline lattice, which is favored when a solution is immobile.
Thus, Stirring the solution Avoids this accumulation, maximizing dissolution (types of saturation, 2014).
Saturation and solubility curves
Solubility curves are a graphical database where the amount of solute that dissolves in an amount of solvent at a given temperature is compared.
Solubility curves are commonly plotted for an amount of solute either solid or gas in 100 grams of water (Brian, 2014).
Figure 2 illustrates the saturation curves for several solutes in water.
In the axis of the coordinates we have the temperature in degrees centigrade, and in the axis of the abscissa we have the concentration of solute expressed in grams of solute per 100 grams of water.
The curve indicates the saturation point at a given temperature. The area below the curve indicates that there is an unsaturated solution and therefore more solute can be added.
The area above the curve has a supersaturated solution. (Solubility Curves, s.f.)
Taking as an example sodium chloride (NaCl), at 25 degrees centigrade approximately 35 grams of NaCl can be dissolved in 100 grams of water to obtain a saturated solution. (Cambrige University, s.f.)
Examples of saturated solutions
Saturated 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. The following are examples of everyday saturated solutions:
- Soda and sodas in general are saturated solutions of carbon dioxide in water. That is why, when the pressure is released, bubbles of carbon dioxide form.
- Soils are saturated with nitrogen.
- You can add sugar or salt to the vinegar until it forms a saturated solution.
- Adding powdered chocolate to the milk until it does not dissolve forms a saturated solution.
- Milk can be saturated with flour to the point that no more flour can be added to the milk.
- Melted butter can be saturated with salt, when the salt no longer dissolves.
What is a supersaturated solution?
The definition of a supersaturated solution is one that contains more solute dissolved than would normally dissolve in the solvent. This is usually done by increasing the temperature of the solution.
A slight alteration of the solution or introduction of a"seed"or tiny solute crystal will force the crystallization of excess solute. If there is no nucleation point for crystal formation, excess solute may remain in solution.
Another form of supersaturation can occur when a saturated solution is carefully cooled. This change in conditions means that the concentration is actually greater than the saturation point, the solution has been supersaturated.
This can be used in the recrystallization process to purify a chemical: it dissolves to the point of saturation in hot solvent, then as the solvent cools and the solubility decreases, excess solute precipitates.
Impurities, which are present in a much lower concentration, do not saturate the solvent and thus remain dissolved in the liquid.
References
- Anne Marie Helmenstine, P. (2016, July 7). Saturated Solution Definition and Examples . Retrieved from about: about.com
- Cambridge University. (S.f.). Solubility curves . Retrieved from dynamicscience.com: dynamicscience.com.au.
- Examples of Saturated Solution . (S.f.). Retrieved from yourdcitionary: examples.yourdictionary.com.
- , S. (2014, June 4). Saturated and Supersaturated Solutions . Retrieved from socratic.org: socratic.org.
- James, N. (s.f.). Saturated Solution: Definition & Examples . Retrieved from study.com: study.com.
- , B. (2014, October 14). Saturated and Supersaturated Solutions . Retrieved from socratic.org: socratic.org.
- Solubility Curves . (S.f.). Retrieved from KentChemistry: kentchemistry.com.
- Types of saturation . (2014, June 26). Retrieved from chemistry libretex: chem.libretexts.org.