Every time we mix a substance with a solvent , we can have several results. The determining factor to obtain these results is the solubility of the substance, which is defined as the maximum possible concentration of the solute. Solubility rules help determine which substances are soluble and to what extent. The degree of solubility can vary widely depending on the substances , and can range from infinitely soluble or totally miscible substances , such as ethanol in water, to poorly soluble , such as silver chloride in water.
What is solubility?
It is the degree to which a substance can be dissolved in a solvent to form a solution , which is generally expressed in grams of solute per liter of solvent .
- Solubility properties
- Factors Affecting Solubility
- What is it for
Solubility is a measure that has the ability of a certain substance to be able to dissolve in another. The substance that dissolves is then known by the name of solute , while the substance in which it dissolves is called a solvent or solvent . When we talk about solubility we also talk about concentration , which refers to the ratio that exists between the amount of solute and the amount of solvent in a solution . It can be expressed through the percentage of solute or in units such as moles per liter orgrams per liter. It is important to note that not all substances dissolve in the same solvents.
Many of the properties that solutions have depend mainly on the concentration of the solutions and when a solute is added to a solvent , some physical properties of the solvent are altered. Some of these properties are as follows:
- When the increases amount of the solute , up the point of boiling and lowers the point of solidification , but when a solute is added the vapor pressure of the solvent is lowered.
- It has the ability to exert an osmotic pressure so if we separate two solutions of different concentrations by a semi-permeable membrane, the solvent molecules will go from the less concentrated solution to the more concentrated one, making it more dilute.
- The particles that participate in the solubility are homogeneous , this means that they have a single phase .
When a solid or a liquid dissolves, the molecules separate and the space between them is occupied by a molecule of the solvent . During this process, energy must be added to overcome the intermolecular forces , which arise from the union between solute particles and solvent molecules. In the dissolution process, each ion is surrounded by several molecules of the solvent and a solvent in order to dissolve the ionic compounds needs to have a high dielectric constant, in other words, it must have very insulating properties. to reduce the attraction between the ions of opposite charge once they are solvated.
Factors Affecting Solubility
Among the different factors that can affect the solubility of a substance, we can mention the following:
- Temperature: can only modify the solubility of solid and gaseous solutes . In the case of solids, an increase in temperature causes an increase in solubility, although some may suffer only a small variation and in some cases when the temperature increases, the solubility decreases . In gases, the increase in temperature decreases the solubility and vice versa.
- Pressure: does not alter the solubility of solids and liquids. It considerably modifies the solubility of the gas when the pressure increases as long as the temperature remains constant . This modification is known as “ Henry’s law ” which says: “The solubility of a gas is directly proportional to the pressure of the gas on the surface of the liquid at constant temperature” .
- The chemical nature of the solute and the solvent : tells us that a substance can be quite soluble with a certain solvent but this situation does not ensure that it is so with other solvents .
There are three different types of solubility, these are
- Soluble : They are substances that have a solubility greater than 0.02 moles of solute per liter of solution.
- Slightly insoluble : are those substances that have an approximate solubility of 0.02 moles per liter .
- Insoluble : They are substances that have a solubility of less than 0.02 moles per liter, but since this solubility is not entirely zero, they are usually called by the name of poorly soluble .
What is it for
It helps us to designate and to quantitatively express the concentration of solutions. In addition, it measures the dissolution capacity of the different substances that make up the compounds.
Some examples that we can observe of the solubility of substances are the following:
- Soluble in water:
- Salt : or sodium chloride, is ordinarily soluble in water at 20 ° C.
- Alcohol : both ethyl and isopropyl.
- Wine : it is a mixture of alcohol and fermented fruit.
- Soap : because it has carbon, hydrogen and salt in its composition, it can dissolve when it comes into contact with water.
- Ammonia : can be observed in household cleaning products.
- Oxygen : this gas dissolved in water is what aquatic animals breathe.
- Sugar : it is ordinarily soluble in water at 20 ° C.
- Soluble in other substances:
- Mayonnaise : mixture of egg, vinegar and salt in oil.
- Paints, lacquers and stains : they dissolve in thinner or acetone.
- Plastic : reacts to organic solvents based on ethylene glycol.
- Glue : dissolves in formaldehyde.
- Resins and gums : dissolved in toluene.
- Rubber and leather : can be dissolved in xylene.