We explain what a chemical solution is and its main characteristics. Also, how it is classified and what the concentration is.
What is a chemical solution?
It is called a chemical solution or solution. a homogeneous mixture of two or more pure chemicals. A dissolution can occur at the molecular or ionic level and is not a chemical reaction.
In this way, the solution resulting from the mixture of two components will have a single recognizable phase (solid, liquid or gaseous) even though its separate components had different phases. For example, when dissolving sugar in water.
Every chemical solution has at least two components: a solute (which is dissolved in the other) and a solvent or solvent (which dissolves the solute). In the case of sugar dissolved in water, the sugar is the solute and the water is the solvent.
The formation of solutions and mixtures of substances is fundamental for the development of new materials and for the understanding of the chemical forces that allow matter to combine. This is of particular interest for the fields of chemistry, biology and geochemistry, among others.
See also: Enthalpy
Characteristics of a chemical solution
In general, every chemical solution is characterized by:
- Solute and solvent cannot be separated by physical methods such as filtration or sieving, since their particles have formed new chemical interactions.
- They have a solute and a solvent (at least) in some detectable proportion.
- At first glance its constituent elements cannot be distinguished.
- Only solute and solvent can be separated by methods such as distillation, crystallization or chromatography.
Types of chemical solution
Chemical solutions can be classified according to two criteria.
The ratio between the solute and the solvent:
- Diluted When the amount of solute with respect to the solvent is very small. For example: 1 gram of sugar in 100 grams of water.
- Concentrated When the amount of solute relative to the solvent is large. For example: 25 grams of sugar in 100 grams of water.
- Saturated When the solvent no longer accepts any more solute at a certain temperature. For example: 36 grams of sugar in 100 grams of water at 20 °C.
- Oversaturated Since saturation has to do with temperature, if we increase the temperature, the solvent can be forced to take up more solute than it ordinarily can, obtaining a supersaturated solution (oversaturated, let's say). Thus, subjected to heating, the solution will take up much more solute than it ordinarily could.
The aggregation status of the components:
Solid:
- Solid in solid. Both the solute and the solvent are in a solid state. For example: alloys such as brass (copper and zinc).
- Gas in solid The solute is a gas and the solvent is a solid. For example: hydrogen in palladium, volcanic dust, among others.
- Liquid in solid The solute is a liquid and the solvent is a solid. For example: amalgams (mercury and silver)
Liquids:
- Solid in liquid Typically, small amounts of solid (solute) are dissolved in a liquid (solvent). For example: sugar dissolved in water.
- Gas in liquid. A gas (solute) is dissolved in a liquid (solvent). For example: the oxygen dissolved in seawater which is responsible for aquatic life on the planet.
- Liquid in liquid. Both the solute and the solvent are liquids. For example: amalgams (mercury and silver)
Soft drinks:
- Gas in gas. Both the solute and the solvent are gases. In many cases these solutions are assumed to be mixtures due to the weak interactions between the gas particles. For example: oxygen in air.
- Gas in solid The solute is a gas and the solvent is a solid. For example: dust dissolved in air.
- Liquid in gas The solute is a liquid and the solvent is a gas. For example: water vapor in the air.
Concentration of a chemical solution
Concentration is a quantity that describes the proportion of solute to solvent in a solution. This magnitude is expressed in two different types of units:
Physical units Those that are expressed in relation to the weight and volume of the solution, in percentage form (multiplied by 100). For example:
- %Weight/weight It is expressed in grams of solute per grams of solution.
- %Volume/volume It is expressed in cubic centimeters (cc) of solute over cc of solution.
- %Weight/volume Combine the previous two: grams of solute over cc of solution.
Chemical units Those that are expressed in systems of chemical units. For example:
- Molarity (M) It is expressed as the number of moles of solute in one liter of solution or one kilogram of solution. It is calculated as follows:
Where n(X) is the number of moles of component Vdissolution is the volume of the solution. Molarity is expressed in moles/L solution. - Mole fraction (Xi) It is expressed in terms of moles of a component (solvent or solute) in relation to the total moles of the solution, as follows:
Xsolution = moles of solute / (moles of solute + moles of solvent)
Xsolvent = moles of solvent / (moles of solute + moles of solvent)Always contemplating that:
Xsolvent + Xsolution = 1
The mole fraction is dimensionless, that is, it is not expressed in units of measurement. - Molality (m) It is the ratio between the number of moles of any solute dissolved per kilograms of solvent. It is calculated as follows:
Where m(X) is the molality of n(X) is the number of moles of X and mass (solvent) is the mass of solvent expressed in kg. It is important to clarify that molarity is expressed per kg (1000g) of solvent. It is expressed in units of mol/kg.
References
- Chemistry. Márquez, Eduardo J. Martínez.Cengage Learning Editores. (2010) ISBN 6074811652.
- General chemistry. Christen, Hans Rudolf. I reversed. (1977) ISBN 9788429171310.
