Chemical impurity removal, specific examples, to be complete.

Separation of several substances in a mixture to obtain relatively pure substances is called separation of mixtures. Removing impurities mixed in substances to obtain pure substances is called purification or impurity removal. Impurity removal is a common problem in junior high school chemistry, which is flexible and changeable and can comprehensively examine students' problem-solving ability. Now list several methods:

1 physical method

1.l filtration method. Principle: The method of separating insoluble solids from liquid by filtration is called filtration. For example, calcium chloride contains a small amount of calcium carbonate impurities. First, the mixture is dissolved in water. Because calcium chloride is soluble in water and calcium carbonate is insoluble in water, calcium carbonate is removed by filtration, and then the filtrate is evaporated to obtain solid calcium chloride. If impurity calcium carbonate is to be obtained, it can be washed and dried.

Exercise 1 The following mixture can be separated by dissolution, filtration and evaporation: ()

A. calcium carbonate, calcium oxide, sodium chloride, potassium nitrate, sodium nitrite, barium sulfate, KCl and potassium chloride.

1.2 crystallization method. Principle: The mixture of several soluble solid substances can be crystallized and separated according to their solubility in the same solvent or the change trend of solubility with temperature. For example, after removing sodium chloride impurities mixed in solid potassium nitrate, a saturated solution of potassium nitrate is prepared at a higher temperature and then gradually cooled. Because the solubility of potassium nitrate increased significantly with the increase of temperature, the temperature decreased, and most of potassium nitrate was precipitated in the form of crystals, while the solubility of sodium chloride did not increase significantly with the increase of temperature, so most of sodium chloride remained in the mother liquor, and potassium nitrate and sodium ammoniated solution were separated by filtration. In order to further purify potassium nitrate, this operation can be repeated again, called recrystallization or recrystallization.

Exercise 2 The following mixture is suitable for crystallization separation: ()

A.nano 3 na2co 3 B nano 3 NaCl C NaOH Mg(OH)2D NaCl baso 4

2. Chemical method: principle

(1) The added reagent only reacts with impurities and does not react with the original substance.

(2) No new impurities can be introduced after the reaction.

(3) Recover after the reaction.

(4) The operation method is simple and easy.

Chemical impurity removal methods commonly used in junior high schools are as follows:

2. 1 precipitation method: impurities in the mixture react with appropriate reagents, and the generated precipitate is removed by filtration.

Exercise 3 The following mixture can be removed by precipitation (the substance in brackets is impurity) is ()

A. potassium nitrate [ba (NO3) 2] b sodium chloride [kno3] c sodium nitrite [NaCl] d calcium nitrate AgCl

2.2 Gasification method: Impurities in the mixture react with appropriate reagents, and become gases to be removed.

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

Exercise 4 Impurities in the following mixture (substances in brackets are impurities) are suitable to be removed by gas method: ()

A.nano 3〔Ba(NO3)2〕B . NaCl[Mg(OH)2]C . kno 3〔k2co 3〕D . na2so 4〔mgso 4〕

2.3 Displacement method: Impurities and appropriate reagents in the mixture are removed by displacement reaction. For example, zinc sulfate solids contain a small amount of copper sulfate impurities. After dissolution, a proper amount of zinc powder is added, then the replaced copper is removed by filtration, and the filtrate is evaporated to obtain copper sulfate solid.

Exercise 5 Which of the following substances can remove a small amount of impurity copper sulfate () mixed in ferrous sulfate solution?

A. zinc, boron, iron, carbon, copper, cadmium and magnesium

Exercise 6: Dissolve copper sulfate crystal mixed with a small amount of iron powder and zinc in appropriate amount of water, and filter completely. The results are as follows

A. filter out the mixed iron powder B. filter out the mixed zinc powder C. filter out some copper powder D. filter out nothing.

2.4 Absorption method: When impurities in two or more mixed gases are absorbed by a solvent or solution, but the gas to be purified cannot be absorbed, this method can be adopted.

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

2.5 Other methods: the impurities in the mixture are converted into other substances by chemical methods.

For example, calcium oxide contains calcium carbonate, which can be decomposed into calcium oxide and carbon dioxide after high temperature combustion, and carbon dioxide can be diffused into the air to remove impurities.

Your question is not very clear, but it can be summarized as follows:

1. Remove liquid from liquid: physical crystallization, such as sodium nitrate mixed in sodium chloride; Precipitation method: kno 3 [ba (NO3) 2] (adding Na2SO4); Gasification method: mixing sodium carbonate in sodium chloride solution (adding dilute hydrochloric acid); Alternative method,

FeCl2 & ltCuCl2 & gt (adding Fe)

2, removing solids from solids: dissolving and filtering method, CaCO3 < Cao >；; Gasification method: mixing sodium carbonate in sodium chloride solution (adding dilute hydrochloric acid); Alternative method,

Cu & ltFe & gt (adding CuCl2).

3. Removing gas from gas: absorption method (see 2.4); Other methods: such as CO2 < CO > passing through hot copper oxide.

This is a general way to remove impurities, do you understand? I hope you have something!