What Does Chemical solution Mean
We explain what a chemical solution is and its main characteristics. Also, how is it classified and what is concentration.
What is a chemical solution?
It is called solution or chemical solution to one homogeneous mixture of two or more pure chemicals . Dissolution can occur at the molecular or ionic level and does not constitute a chemical reaction .
In this way, the solution resulting from the mixture of two components will have a single recognizable phase ( solid , liquid or gas ) even though its separate components have different phases. For example, by 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, sugar is the solute and 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 to the fields of chemistry , biology, and geochemistry, among others.
See also: Enthalpy
Characteristics of a chemical solution
In general, any 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 a minimum) in some detectable proportion.
- Its constituent elements cannot be distinguished with the naked eye.
- 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 of solute to 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 with respect to the solvent is large. For example: 25 grams of sugar in 100 grams of water.
- Saturated. When the solvent no longer accepts 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, we can force the solvent to take in more solute than it ordinarily can, obtaining a supersaturated solution (saturated in excess, 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 on solid. Both the solute and the solvent are in the solid state. For example: alloys such as brass ( copper and zinc).
- Solid gas. 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. Generally, 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: dissolved oxygen in seawater that is responsible for aquatic life on the planet.
- Liquid in liquid. Both solute and solvent are liquid. For example: amalgams (mercury and silver)
Sodas:
- Gas into gas. Both solute and solvent are gases. On many occasions these solutions are assumed as mixtures due to the weak interactions between the gas particles. For example: oxygen in air .
- Solid gas. 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 ratio 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, as a percentage (multiplied by 100). For example:
- % Weight / weight. It is expressed in grams of solute over 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 over one liter of solution or one kilogram of solution. It is calculated as follows:
Where n (X) is the number of moles of component X and Vsolution is the volume of the solution. Molarity is expressed in moles / L solution.
- Molar 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 dissolved solute per kilograms of solvent. It is calculated as follows:
Where m (X) is the molality of X, 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.