- Types
- Empirical solutions
- Valued solutions
- According to its state of aggregation
- Preparation
- To prepare standard solutions
- To prepare a dilution of known concentration
- Examples
- References
The chemical solutions are known as homogeneous mixtures in chemistry. They are stable mixtures of two or more substances in which one substance (called solute) dissolves in another (called solvent). The solutions adopt the solvent phase in the mixture and can exist in solid, liquid and gaseous phases.
In nature there are two types of mixtures: heterogeneous mixtures and homogeneous mixtures. Heterogeneous mixtures are those in which there is no uniformity in their composition, and the proportions of their components vary across samples of them.
On the other hand, homogeneous mixtures (chemical solutions) are mixtures of solids, liquids or gases - in addition to possible unions between components that are in different phases - that have their components divided in equal proportions through their content.
Mixing systems tend to seek homogeneity, such as when a colorant is added to water. This mixture starts out heterogeneous, but time will cause the first compound to diffuse through the liquid, causing this system to become a homogeneous mixture.
Solutions and their components are seen in everyday situations and at levels ranging from industrial to laboratory. They are objects of study because of the characteristics they present and because of the forces and attractions that occur between them.
Types
There are several ways to classify solutions, due to their multiple characteristics and their possible physical states; This is why you must know what the differences between the types of solutions are based on before separating them into categories.
One of the ways to separate the types of solution is by the level of concentration that it has, also called the saturation of the solution.
Solutions have a quality called solubility, which is the maximum amount of solute that can be dissolved in a given amount of solvent.
There is a classification of solutions by concentration, which divides them into empirical solutions and titrated solutions.
Empirical solutions
This classification, in which the solutions are also called qualitative solutions, does not take into account the specific amount of solute and solvents within the solution but rather their proportion. For this, the solutions are separated into dilute, concentrated, unsaturated, saturated and supersaturated.
- Diluted solutions are those in which the amount of solute in the mixture is at a minimum level compared to the total volume of the mixture.
- Unsaturated solutions are those that do not reach the maximum possible amount of solute for the temperature and pressure at which they are found.
- Concentrated solutions have considerable amounts of solute for the volume that has been formed.
- Saturated solutions are those that have the largest possible amount of solute for a given temperature and pressure; in these solutions, the solute and the solvent present an equilibrium state.
- Supersaturated solutions are saturated solutions that have been heated to increase solubility and dissolve more solute; A "stable" solution with excess solute is then generated. This stability only occurs until the temperature drops again or the pressure changes drastically, a situation in which the solute will precipitate in excess.
Valued solutions
The titrated solutions are those in which the numerical amounts of solutes and solvent are measured, observing the percent, molar, molar and normal titrated solutions, each with its series of measurement units.
- The percentage values speak of the proportion in percentage of grams or milliliters of solute in one hundred grams or milliliters of total solution.
- Molar concentrations (or molarity) express the number of moles of solute per liter of solution.
- Molality, little used in modern chemistry, is the unit that expresses the number of moles of a solute divided by the total mass of solvent in kilograms.
- Normality is the measure that expresses the number of solute equivalents between the total volume of solution in liters, where the equivalents can represent the ions H + for acids or OH - for bases.
According to its state of aggregation
Solutions can also be classified by the state in which they are found, and this will depend mainly on the phase in which the solvent is found (the component present in the greatest quantity within the mixture).
- Gaseous solutions are rare in nature, classified in the literature as gas mixtures rather than as solutions; they occur under specific conditions and with little interaction between their molecules, as in the case of air.
- Liquids have a wide spectrum in the world of solutions and represent the majority of these homogeneous mixtures. Liquids can dissolve gases, solids, and other liquids with ease, and are found in all kinds of everyday situations, naturally and synthetically.
There are also liquid mixtures that are often confused with solutions, such as emulsions, colloids and suspensions, which are more heterogeneous than homogeneous.
- Gases in liquid are mainly observed in situations such as oxygen in water and carbon dioxide in carbonated beverages.
- Liquid-liquid solutions can be presented as polar components that dissolve freely in water (such as ethanol, acetic acid and acetone), or when a non-polar fluid dissolves in another with similar characteristics.
- Finally, solids have a wide range of solubility in liquids, such as salts in water and waxes in hydrocarbons, among others. Solid solutions are formed from a solid phase solvent, and can be seen as a means of dissolving gases, liquids, and other solids.
Gases can be stored within solids, such as hydrogen in magnesium hydride; liquids in solids can be found as water in sugar (a wet solid) or as mercury in gold (an amalgam); and solid-solid solutions are represented as alloys and composite solids, such as polymers with additives.
Preparation
The first thing that must be known when preparing a solution is the type of solution to be formulated; that is, you must know if you are going to make a dilution or prepare a solution from the mixture of two or more substances.
Another thing to know is what are the known values of concentration and volume or mass, depending on the state of aggregation of the solute.
To prepare standard solutions
Before starting any preparation, make sure that the measuring instruments (balance, cylinders, pipettes, burettes, among others) are calibrated.
Next, the amount of solute in mass or volume is started to be measured, taking great care not to spill or waste any quantity, as this would affect the final concentration of the solution. This must be introduced into the flask to be used, preparing now for the next stage.
Subsequently, the solvent to be used is added to this solute, making sure that the content of the flask reaches the capacity of the same.
This flask is stoppered and shaken, making sure to invert it to ensure effective mixing and dissolution. In this way the solution is obtained, which can be used in future experiments.
To prepare a dilution of known concentration
To dilute a solution and lower its concentration, more solvent is added in a process called dilution.
Through the equation M 1 V 1 = M 2 V 2, where M symbolizes the molar concentration and V the total volume (before and after dilution), the new concentration can be calculated after diluting a concentration, or the required volume to achieve the desired concentration.
When preparing dilutions, the stock solution is always taken to a new, larger flask and solvent is added to it, making sure to reach the gauging line to guarantee the desired volume.
If the process is exothermic and therefore presents safety risks, it is best to reverse the process and add the concentrated solution to the solvent to avoid splashing.
Examples
As mentioned above, solutions come in different states of aggregation, depending on the state in which their solute and solvent are found. Examples of these mixtures are listed below:
- Hexane in paraffin wax is an example of a liquid-solid solution.
- Hydrogen in palladium is a gas-solid solution.
- Ethanol in water is a liquid-liquid solution.
- Common salt in water is a solid-liquid solution.
- Steel, composed of carbon atoms in a crystalline matrix of iron atoms, is an example of a solid-solid solution.
- Carbonated water is a gas-liquid solution.
References
- Wikipedia. (sf). Solution. Retrieved from en.wikipedia.org
- TutorVista. (sf). Types of Solutions. Retrieved from chemistry.tutorvista.com
- cK-12. (sf). Liquid-Liquid Solution. Retrieved from ck12.org
- Faculty, U. (sf). Solution Preparation. Retrieved from faculty.sites.uci.edu
- LibreTexts. (sf). Preparing Solutions. Retrieved from chem.libretexts.org