purification[1]It refers to separating impurities in the mixture to improve its purity.As an important chemical method, purification plays an important role not only in chemical research, but also in chemical production.Many important chemical research and chemical production are based on purification.Common physical and chemical purification methods are introduced in detail.
The purification of substances is to remove impurities in the mixture to obtainPure substanceProcess.If impurities occur during purificationChemical changeIt is not necessary to revert to the original substance.
It is mainly divided into physical methods and chemical methods.
Physical methods
Announce
edit
extraction
UtilizesoluteWith different solubility in mutually insoluble solvents, one solvent is used to extract the solute from the solution composed of it and another solvent, and thenLiquid separationThe principle and method of[2]。
filter
Filtration: it is a method to separate insoluble solids from solutions by making use of the difference in solubility of each component of the mixture in the same solvent.Such as the purification of crude salt.
Evaporation concentration
Evaporation concentration: it is a method for separating solutes dissolved in solvents[3]。Such as separating NaCl in salt solution.
Crystallization and recrystallization
Crystallization and recrystallization: it is a method of separating and purifying substances by using the properties that the solubility of each component in a mixture changes with temperature in a certain solvent.Such as separation of NaCl and KNO3 mixture.Recrystallization is actually the operation of repeated dissolution and crystallization..
Distillation and fractionation
Distillation and fractionation: It is a method of separating substances by using the properties of several mutually soluble liquids with large differences in boiling points[4]。For example, separation of various fractions from petroleum, and separation of C2H5OH and H2O mixture.
Liquid separation
Liquid separation: it is a method of separating substances by using the properties of two immiscible liquids with different densities.Such as separation of C6H6 and H2O mixture.
Flotation method
Flotation method: it is used to separate solid mixtures that are insoluble in water solvents by using different density of substances.Such as using water to seek gold in the sand.
sublimation
Sublimation: It is a method to separate the mixture by using some components in the mixture that can be directly converted into gas at a certain temperature, and then directly converted into solid after cooling. In fact, it is to separate the mixture by using the nature of sublimation.For example, I2 is separated and purified from the mixture of NaCl and I2.
liquefaction
Liquefaction: It is a method to separate the mixture by making use of the different boiling points of various gases to liquefy them before gasification.For example, N2 and O2 are separated from air.
washing
Water washing: it is a method of separating and purifying substances by using the different solubility of each component gas in water.For example, HCl gas is removed from the mixture of H2 and HCl gas.
Dialysis method
Dialysis method: This method is to separate ions or small molecules from colloidal solution by using a semipermeable membrane.For example, separating KI from starch[5]。
Salting out
Salting out: It is a method to separate some substances by using the property of precipitation formed by the decrease of their solubility when adding some inorganic salts.For example, separating soap and glycerin from saponification solution, and then salting out protein.
paper chromatography
Paper chromatography: It is a method of separating and identifying mixtures containing trace substances by using filter paper or other substances with capillary effect under the action of developing agent.Chromatography is based on the differences in physical and chemical properties of each component in the mixture (such as adsorption force, molecular shape and sizeMolecular affinity、partition coefficientAnd so on), so that each component is in two phases (one phase is fixed, called stationary phase; the other phase flows through the stationary phase, calledmobile phase）The distribution degree in the is different, so that each component moves at different speeds to achieve the purpose of separation.For example, separating the mixture containing a small amount of Fe3+and Cu2+:
Mixture (Fe3+and Cu2+) outer ring (yellow ring Fe3+), inner ring (blue ring Cu2+)
chemical method
Announce
edit
Thermal decomposition method
Thermal decomposition method: it uses the different stability of each component in the mixture to heat or cauterize it to separate substances.If NaHCO3 mixed in Na2CO3 is removed[6]。
Acid and alkali treatment
Acid and alkali treatment: it is a method to separate substances by treating them with alkali or acid according to the different acid-base properties of each component in the mixture.For example, the mixture of Al2O3 and Fe2O3 is separated.
Acid and alkali treatment
Precipitation method
Precipitation method: it is a method of separating or purifying substances by using a certain component in the mixture to react with the solution to generate precipitation.For example, a small amount of KCl in KNO3 can be removed by adding an appropriate amount of AgNO3 solution.
Redox method
Redox method: It is a method of separating or purifying substances by using the nature that a certain component in the mixture can be oxidized (or reduced).If toluene mixed in benzene is removed[7]。
Redox method
Complexation method
Complexation method: it is a method of separating and purifying substances by using the properties of a certain component in the component that can form a complex.For example, the mixture of Al2O3 and ZnO is separated.
Complexation method
Electrolytic method
Electrolysis: It is a method of separating and purifying substances by using the principle of electrolysis, such as electrolytic smelting of aluminum.
