Aqueous solution

In Chemistry, a aqueous solution is a phase liquid containing several chemical species, including one ultramajoritaire, the Eau (H ₂ O, the Solvant), and of the species ultraminoritaires, the Solutés or “chemical species dissolved”.

The study of the aqueous solutions constitutes the major part of chemistry.

Solvent properties of water

Water is a good solvent because:

it has a electric Permittivité important ε_C, which is worth approximately 80 with 20 °C, it thus divides by 80 the forces of interaction between the molecules and the atoms, thus obstructing an electrostatic cohesion;

the molecule of water is polar, therefore, if the species is charged or if it has partially charged sites, the water molecules are bound there, forming a kind of “shield”; one speaks about Hydratation, or in the general case of Solvatation.

These properties are due to the electric charges which are on each atom of the water molecule. The oxygen atom is électonégatif because of its double not-binder of electrons. The hydrogen atoms are rather electropositive, because the proton is rather far away from oxygen. Thus, the water molecule can allow the formation of small sufficiently strong electrostatic bridges to dissolve a polarized compound.

The solvation of the aqueous solutions in aqueous solution

Saturated solution

A Saturated Solution is obtained by dissolution of an aqueous solution in a solvent; the solution is saturated when the introduced aqueous solution cannot dissolve any more and forms a deposit.

; Examples

One uses solutions saturated with KCl to preserve the electrode S out of glass of the PH-mètre S.

One of the electrodes standardized for the electrochemistry is the calomel electrode saturated with KCl (ECS).

Ionic solution

An ionic solution is a solution in which the dissolved species are ions.

Solubilization of the organic compounds

Each compound does not have the same capacity to be made dissolve by water, nor in the same quantities. It depends:

of the number of polar groupings: it must be of sufficient and majority number on the non-polar groupings to allow a solubilization of the compound.
of the size: the macromolecules dissolve with difficulty in water, even if they have a number of polar groupings important (ex: the Starch)

Criteria of solubility of a compound in water

Compound molecular

Ionic compounds

Uses

Aqueous solutions in electrochemistry

Water is a solvent of choice to carry out electrolyzes and other electrochemical reactions because of are strong dissociating capacity correlated with its great stability.

Piles and accumulators

Corrosion

Out of metallurgy

Although many metals are oxydable by water or corrode in the presence of water, that Ci remains a fluid and an essential solvent for the ore processing out of metallurgy.

Electrochemical purification

A method of acquisition very pure metal is master key by an electrolysis or the anode is out of impure metal and cathode out of pure metal. This process also makes it possible with a good choice of the tension of work to recover and develop the impurities (gold and money in the case of copper)

See also: electrochemical Purification of copper

The separation of the ores

A big step of the metallurgy of many metals like lead, lanthanides or the mine of platinum passes by a setting in solution then selective precipitations to insulate each metal present in the ore.

Water like solvent in organic chemistry

A solvent of reaction

A solvent of separation

Use of water supercritical

See too

Acid, bases
Dissolution
Électrolyte
Gaz of blood
Gaz in metals

External bonds

aqueous

Ionic Solutions Don' T Look Like That! , of the site Bad Chemistry of the University of Princeton

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