How Do You Remove Impurities in Chemistry?

For chemical synthesis companies, the removal of impurities is a normal operation. Actually, in chemistry, there are not only chemical ways but also physical ways to purify compounds. Follow molcreator to see these purification methods now.

List of purification methods in chemistry— physical methods

1. Filtering method

Principle: The method of separating solids and liquids that are insoluble in liquids by filtering is called the filtering method.

For example, if calcium chloride contains a small amount of calcium carbonate impurities, first dissolve the mixture with water. Since calcium chloride is soluble in water, but calcium carbonate is hard to dissolve in water, filter to remove the impurity calcium carbonate, and then evaporate the filtrate to obtain solid calcium chloride. If you want to obtain impurity calcium carbonate, it can be washed and dried. The filtering purification method is a basic one and is mostly seen in the laboratory. 

2. Crystallization

Crystallization is also on the list of purification methods in chemistry. The principle of this purification method is as follows: A mixture of several soluble solid substances can be separated by crystallization according to their solubility in the same solvent or the changing trend of solubility with temperature.

For example, to remove the sodium chloride impurities mixed in solid potassium nitrate, first, make a saturated solution of potassium nitrate at a higher temperature, and then gradually cool it. Because the solubility of potassium nitrate increases significantly with the increase in temperature, and when the temperature decreases, most of the potassium nitrate becomes crystals and the solubility of sodium chloride does not increase significantly with the increase of temperature, so most of the sodium chloride remains in the mother liquor. The potassium nitrate and sodium amide solution are separated by filtering. To further purify potassium nitrate, the operation can be repeated once more, which is named recrystallization. Filtering, as well as crystallization, is the two purification methods using the physical principle.

List of purification methods in chemistry— chemical methods

After the introduction of physical purification methods, let’s turn to the chemical methods. There are several requirements for a successful purification.

a. The added reagent only reacts with impurities, not the original.

b. No new impurities can be brought in after the reaction.

c. Restore the original state after the reaction.

d. The operation method is simple and easy.

And the following is the list of purification methods in chemistry using the chemical principle.

1. Precipitation method

The impurities in the mixture are reacted with appropriate reagents to form precipitates and removed by filtration.

2. Evaporating method

The impurities in the mixture are reacted with appropriate reagents to become gas and removed.

For example, sodium nitrate solid contains a small amount of sodium carbonate impurities, the mixture can be dissolved in water, and then an appropriate amount of dilute nitric acid solution is added. The nitric acid reacts with sodium carbonate to generate sodium nitrate, water, and carbon dioxide, and then the filtrate is evaporated to obtain sodium nitrate solid.

3. Replacement method

The working principle of this purification method is as follows:

The impurities and appropriate reagents in the mixture are removed by a substitution reaction.
For example, zinc sulfate solid contains a small amount of copper sulfate impurities. How to remove the impurity? You can the mixture, add an appropriate amount of zinc powder, then filter to remove the replaced copper, and evaporate the filtrate to obtain copper sulfate solid.

4. Absorption method

This method can be used when impurities in two or more mixed gases are absorbed by a certain solvent or solution, but the gas to be purified cannot be absorbed.

For example, when carbon monoxide contains carbon dioxide, the mixed gas can be passed through a solution containing sodium hydroxide.

5. Other methods

There are also other purification methods deserving your attention. For example, calcium oxide contains calcium carbonate, and high-temperature combustion can be used to decompose calcium carbonate into calcium oxide and carbon dioxide at high temperatures. The carbon dioxide diffuses into the air thus removing impurities.

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