Can a saturated solution be diluted

The water as a solvent

The solving process

In technology, in the household and in nature, water is by far the most important solvent. If you throw a piece of sugar (a solid) into a glass of water, the sugar molecules are distributed in the solvent water. According to Dalton (Dalton model), the sugar molecules mix with the water molecules.

This creates a uniform mixture, the solution. If you keep adding sugar to the water, the point quickly comes where the sugar no longer dissolves and we one saturated solution have received. The undissolved solid sugar, which is now at the bottom of the vessel, is called the bottom body.



The mass of a substance that just dissolves in a certain volume of a solvent is called solubility. It depends on the temperature of the solvent (Fig. 18.3). The thermal movement of the solvent particles and the solid particles plays a role in the solution. It leads to the slow mixing of the two substances (diffusion).

The dissolution process can be accelerated by stirring. When a substance dissolves, heating (heat of solution positive) or cooling (heat of solution negative) can occur. The heat of dissolution of some substances is shown in the table below.



Separation of the solvent and the solute can be achieved by evaporating the solvent (2). The volatile substance can be separated from the less volatile substance by distillation (Fig. 1).



Dependence of solubility on temperature and pressure

The solubility of most solids increases as the temperature of the solvent increases (Fig. 3). The temperature dependence of the dissolution process is typical for a substance. While the solubility of table salt hardly changes with increasing temperature, that of nitre increases very strongly.


The solution of gases in a liquid is called absorption, which increases with increasing pressure and decreases with increasing temperature. This is a general law.


The importance of the solution process for living beings

In living beings, water serves as a solvent for nutrients and other vital substances as a means of transport and aquatic animals breathe the oxygen dissolved in the water. They ingest it with the gills or directly through the skin.

Rivers can be warmed up by the cooling water from power plants or factories, which means that the oxygen content of the rivers decreases (Fig. 4). In order not to endanger the survival of aquatic animals, especially the survival of fish, the discharge of cooling or waste water must not warm up the rivers to more than 28 ° C. If toxins from sewage or as a result of putrefaction processes dissolve in the water, it can lead to mass deaths of fish with dire consequences for the environment.