In junior high school chemistry, it is essential to remove one substance out of two substances

1. Physical methods.

1.Filtration method.

Example 1How to remove sediment from table salt.

Brief analysis: dissolve the salt containing sediment in water, use the salt to dissolve in water and the sediment is insoluble, remove the sediment from the salt by filtration, and then evaporate the filtrate to obtain pure salt.

2.Crystallization.

Example 2How to remove a small amount of sodium chloride in potassium nitrate.

Brief analysis: potassium nitrate containing a small amount of sodium chloride is prepared into a hot saturated solution, using the solubility of potassium nitrate is greatly affected by temperature changes, the potassium nitrate crystals are precipitated by cooling and cooling, and the sodium chloride is left in the mother liquor, and then filtered to obtain pure potassium nitrate crystals.

2. Chemical methods.

1.Precipitation method: the commonly used precipitant is: cation (such as) generally available soluble alkali, with barium salt, with calcium salt.

Example 3How to remove magnesium sulfate from sodium chloride.

Brief analysis: dissolve the mixture in water to obtain a solution containing . The impurities are and , according to which the cation energy of the added reagent can be precipitated with , and the anion energy of the reagent is formed with precipitation.

Therefore, the solution can be added dropwise to the solution until the precipitation is no longer produced, and the pure sodium chloride is obtained by filtering and evaporating the filtrate.

2.Gas method.

Example 4How to remove sodium carbonate from sodium chloride.

Brief analysis: dissolve the mixture in water to obtain a solution containing , in which the impurities are . Pure sodium chloride can be obtained by adding an appropriate amount of hydrochloric acid to convert to remove (of course, it can also be converted to precipitate removal), and then the solution is evaporated.

3.Transformation method.

Example 5How to remove carbon monoxide gas from carbon dioxide gas.

Brief analysis: The mixed gas is fully reacted by calciant copper oxide, which can convert carbon monoxide into carbon dioxide and remove it.

4.Substitution method.

Example 6How to remove copper sulphate from ferrous sulphate.

Brief analysis: dissolve the mixture in water to obtain a solution containing , in which the impurities are . Excess iron powder is added to the mixed solution, and the iron powder undergoes a conversion reaction with , and then filtered, evaporated and crystallized to obtain pure ferrous sulfate.

5.Absorption method: Generally, acid gases are absorbed with alkaline solutions; Alkaline gases are absorbed with acid solutions; Generally, it is absorbed with a scorching copper mesh.

Example 7How to remove carbon dioxide gas from hydrogen.

Brief analysis: carbon dioxide is an acid gas, hydrogen is a neutral gas, the mixed gas is passed through a washing cylinder containing alkali (such as NaOH) solution, carbon dioxide is absorbed and removed.

1. CO2 (CO): Passing the gas through the hot copper oxide, 2. CO (CO2): through a sufficient amount of sodium hydroxide solution.

3. H2 (water vapor): through concentrated sulfuric acid through sodium hydroxide solids.

4. Cuo(C): Burning the mixture in air (in the oxygen stream).

5. Cu (Fe): Add sufficient amount of dilute sulfuric acid.

6. Cu (Cuo): Add sufficient amount of dilute sulfuric acid.

7. Feso4 (CuSO4): Add a sufficient amount of iron powder.

8. NaCl (Na2CO3): add sufficient amount of hydrochloric acid.

9. NaCl (Na2SO4): add sufficient amount of barium chloride solution.

10. NaCl (NaOH): add sufficient hydrochloric acid.

11. NaOH (Na2CO3): add sufficient calcium hydroxide solution.

12. NaCl (CuSO4): add sufficient amount of barium hydroxide solution.

13. Nano3 (NaCl): add a sufficient amount of silver nitrate solution.

14. NaCl (KNO3): evaporation solvent.

15. Kno3 (NaCl): cooling hot saturated solution.

16. CO2 (water vapor): through concentrated sulfuric acid.

1. It can generate substances in different states.

For example, the removal of barium ions in the solution with substances containing sulfate ions can generate precipitates.

2 No new impurities are introduced.

For example, sodium carbonate in sodium chloride should be reheated with hydrochloric acid instead of sulfuric acid.

It is not possible to reduce the number of substances needed.

No other substances that cannot be added that cannot go out.

Some of the methods are as follows.

Two solutions, with another other substance, convert impurities into precipitate, gas, water. can be increased, what is needed.

If the required impurities have one dissolved and one is not, filter directly with water.

Does not affect the substances to be retained.

New impurities that are not easily removed should not be introduced.

The operation must be feasible.

Your topic is a bit vague

Depending on which two substances you are specifically in, the specific problem is analyzed, if the solid-liquid is mixed, it will be directly filtered and then washed and dried or the liquid is volatile and can be directly heated and evaporated, and the solid and solid are generally recrystallized, and the liquid liquid can also be volatile by extracting with different liquid polarity and volatile components.

After thinking about it carefully, there are probably the following methods:

First, the insoluble matter in the liquid, filtered.

2. For substances that have been dissolved, add chemicals that can generate insoluble substances, and finally filter.

3. Other substances in the solid, which can be directly separated (such as red beans in the soybean pile), and those that cannot be separated directly (considering the melting point, melting point, etc.).

Fourth, the liquid in the liquid, such as water and oil mixing, see the specific gravity separation. Like oil floating in water.

In junior high school, all you need to remember is acid, alkali, salt, and oxide.

Acids: The cations produced by ionization are only hydrogen ions.

Base: The only anion produced by ionization is hydroxide ions.

Salt: composed of acid anions and metal cations.

Oxide: Composed of only two elements, one of which is oxygen.

a. The mixture of hard water and soapy water can generate scum, and the mixing of soft water and soapy water quietly produces foam, the phenomenon is different and can be identified, so A is correct;

B. There is the smell of burnt feathers when the wool is burned, and there is no smell of burnt feathers when the slag of polyester is burned.

c. The flame is light blue when hydrogen is burned, and the flame color of natural gas (the main component is methane) is blue, which cannot be identified by igniting and observing the flame color, so C is wrong;

d. Lime water is alkaline, rainwater is slightly acidic, and the colorless phenolphthalein test solution does not change color when it encounters acid, and it turns red when it encounters alkali, which can be identified, so D is correct;

So the answer is: c

C. Test question analysis: a. The mixture of hard water and soapy water can produce scum, and the mixing of soft water and soapy water can produce foam, the phenomenon is different and can be identified, so A is correct; Hail accompanies oaks.

b. There is the smell of burnt feathers when wool burns, and there is no smell of burnt feathers when polyester burns.

c. The flame color of hydrogen and natural gas (the main component of the collapse is methane) is blue, and it cannot be identified by igniting and observing the flame color, so C is wrong;

d. Lime water is alkaline, rainwater is slightly acidic, and the colorless phenolphthalein test solution does not change color when it encounters acid, and it turns red when it encounters alkali, which can be identified, so D is correct;

So the answer is: c

Comments: This question examines the identification of common substances, and the completion of this question can be carried out according to the source of the properties of the substance