Dissolution

A solution or solution is a homogeneous mixture at the molecular or ionic level of two or more pure substances that do not react with each other, whose components are found in variable proportions. It can also be defined as a homogeneous mixture made up of a solvent and one or more solutes.

A common example might be a solid dissolved in a liquid, such as salt or sugar dissolved in water; or even gold into mercury, forming an amalgam. Also other examples of solutions are water vapor in air, hydrogen in palladium or any of the existing alloys.

The term is also used to refer to the dissolution process.

Solvent and Solute

Micela

A solution or solution is a homogeneous mixture of pure substances. Frequently formed by a solvent, solvent, dispersant, or dispersion medium, a medium in which one or more more solutes. The criteria for deciding which is the solvent and which are the solutes are more or less arbitrary; there is no scientific reason to make such a distinction.

Wilhelm Ostwald distinguishes three types of mixtures according to the size of the solute particles in the solution:

• Dispersion, suspensions or false dissolutions: when the diameter of the solute particles exceeds 0.1 μm.
• Dispersoids, coloids: the size is between 0.001 μm and 0.1 μm.
• Dispersed or true dissolutions: the size is less than 0.001 μm.

The latter are classified as:

• Dissolutions with molecular condensation: The scattered particle is formed by a condensation of molecules.
• Molecular Dissolutions: Each particle is a molecule.
• Ionic Dissolutions: The scattered particle is an ion (transmitting molecule with electric charge).
• Atomic Dissolutions: Each scattered particle is an atom.

General characteristics

• They are homogeneous mixtures: the relative proportions of solutes and solvent are kept in any amount we take from the dissolution (as small as the drop), and cannot be separated by solvent centrifuge.
• When the solute dissolves, it becomes part of the dissolution.
• When dissolving a substance, the final volume is different from the sum of the volumes of the solvent and the solute, because the volumes are not additive.
• The amount of solute and the amount of solvent are found in varying proportions between certain limits. Normally the solvent is in greater proportion than the solute, although it is not always so. The proportion in which we have the solute within the solvent depends on the type of interaction between them. This interaction is related to the solubility of the solute in the solvent, that is, it has to do with the amount of solute that is able to admit this solvent.
• The physical properties of the solution are different from those of the pure solvent: the addition of a solute to a solvent increases its boiling point and decreases its freezing point; the addition of a solute to a solvent decreases the steam pressure of this one.
• Their physical properties depend on their concentration:

Dissolution HCl 12 mol/L; density = 1.18 g/cm3

Dissolution HCl 6 mol/L; density = 1.10 g/cm3

• The chemical properties of the components of a dissolution are not altered.
• As these cannot be separated by centrifugation or filtration; their components are obtained through other methods known as fractionation methods, such as distillation or crystallization.

Types of solutions

-- By its aggregation status --

Solids

Examples of liquid dissolutions

• Solid solid solid solid: when both the solute and the solvent are in solid state. A clear example of this type of dissolution is alloys, such as zinc in the tin.
• Gas in solid: an example is hydrogen (gas), which dissolves quite well in metals, especially in the palate (solid). This palate feature is studied as a form of hydrogen storage.
• Solid liquid: when a liquid substance dissolves along with a solid. Amalgams are made with mercury (liquid) mixed with silver (solid).

Liquid

• Liquid solid: This type of dissolutions is the most widely used, as small quantities of solid substances are usually dissolved in large liquid quantities. A clear example of this type is the mixture of water with sugar

• Gas in liquid: for example, oxygen in water or sulfur dioxide in water.
• Liquid fluid liquid: this is another of the most used dissolutions. For example, different mixtures of alcohol in water (change the final density). A method to separate them again is by distillation.

Gas

• Gas in gas: are the most common gaseous dissolutions. An example is air (composed of oxygen and other dissolved gases in nitrogen). Since these solutions hardly produce molecular interactions, the solutions that the gases form are quite trivial. Even part of literature is not classified as solutions, but as mixtures.
• Solid gas: are not common, but as an example you can cite the sublimated iodine dissolved in nitrogen and atmospheric dust dissolved in the air.
• Gas liquid: for example, wet air.

Example

The following is a table with examples of solutions classified by their state of aggregation where some possible combinations are shown:

For his concentration

Vessels are observed which contain red dye which show qualitative changes in concentration. Dissolutions on the left are more diluted, while the most concentrated dissolutions are on the right.

Due to its concentration, the solution can be analyzed in quantitative or qualitative terms depending on its state.

Empirical Solutions

Also called qualitative solutions, this classification does not take into account the numerical amount of solute and solvent present, and depending on the ratio between them they are classified as follows:

• Dissolution diluted: is that where the amount of solute involved is in a minimum proportion in a certain volume.
• Dissolution concentrated: has a considerable amount of solute in a certain volume.

• Dissolution saturated: they have as much solute as possible for a given temperature and pressure. There is a balance between the solute and the solvent.
• Dissolution oversaturated: contains more solute than can exist in balance at a given temperature and pressure. If a saturated solution is heated you can add more solute; if this solution is slowly cooled and not disturbed, you can retain excess solute by becoming an oversaturated solution. However, they are unstable systems, with any disturbance the solute in excess of precipitation and the solution returns to being saturated; this is because they mixed.

Titrated solutions

Unlike empirical solutions, quantitatively titrated solutions do take into account the exact numerical amounts of solute and solvent used in a solution. This type of classification is widely used in the field of science and technology, since high precision is very important in them.

There are three types of valued solutions: ionic, elemental and formulated

• Ionic valued solutions:

They are those in which the components of the solution (the solute and the solvent) form ionic bonds. This means that two or more linked ions are present. Of these ions, one is positively charged (called a cation) and the other is negatively charged (called an anion).

• Elementary valued solutions:

These solutions are made up of elements in their pure state and are obtained from solutions of other compounds.

• Valued solutions formulated:

These solutions are based on calculating the atomic weight and the number of elements present in the solution.

Applied knowledge

Depending on the nature of solutes and solvents, the laws governing solutions are different.

• Solid solids: Laws on solid dissolutions.
• Liquid Solids: Solubility Laws.
• Fuels in gases: Brownian movements and coloid laws.
• Liquids: Interfacial tension.
• Liquid gas: Henry's law.