High school chemistry about the separation of substances summary

Adsorption, precipitation, filtration, distillation, fractionation, dry distillation, extraction.

The main separation and purification methods in high school are as follows:

Crystallization and recrystallization.

nacl(kno3)

Impurities are in parentheses, the same below.

Distilled ethanol (water): Add enough fresh CAO and then distill filter NaCl solution (CaCO3).

Sublimation of NACL

i2) Iodine is removed by heating.

kno3（nh4cl）

Extraction method: The bromine element in bromine water is extracted with benzene ccl4.

Dissolved iron (Al).

Add sodium hydroxide solution to dissolve aluminum.

Saturated sodium bicarbonate solution for increasing CO2 (SO2);

Co (CO2) with scorching C

For example, in the conversion method, Fe(OH)3 is separated, and a sufficient amount of sodium hydroxide solution is added to remove Al(OH)3 and Fe(OH)3 is separated

Excess CO2 was then introduced into the sodium tetrahydroxyaluminate solution to convert it to Al(OH)3FeCl2 (FeCl3).

Add iron powder; FeCl3 (FeCl2) is introduced into the solution

The main separation and purification methods in high school are as follows:

1 Crystallization and recrystallization NaCl(KNO3) are impurities in parentheses, the same below.

2 Distillation Ethanol (water): Add enough fresh CAO and then distill.

3 Filter NaCl solution (CaCO3).

4 Sublimation of NaCl (I2) Iodine Kno3 (NH4Cl) is removed by heating

5 Extraction method The bromine element in bromine water is extracted with benzene ccl4.

6 Dissolution method Iron(Al) Add sodium hydroxide solution to dissolve aluminum.

7 Saturated sodium bicarbonate solution for CO2 (SO2) in addition method; Co (CO2) with scorching C

8 Conversion method For example, to separate Fe(OH)3, add sufficient sodium hydroxide solution to remove Al(OH)3 and separate Fe(OH)3

Excess CO2 is then introduced into the sodium tetrahydroxyaluminate solution to convert it to Al(OH)3

FeCl2 (FeCl3) with iron powder; FeCl3 (FeCl2) is introduced into the solution

Crystallization, recrystallization, extraction of liquids, filtration, distillation, fractionation.

1: Extraction, 2: Distillation.

3: Sublimation. 4: Crystallization (or precipitation).

5: Sometimes there will be a little solution, electroplating and so on.

Filtration, extraction, centrifugation, crystallization, fractionation...

The main separation and purification methods in high school are as follows:

1 Crystallization and recrystallization NaCl(KNO3) are impurities in parentheses, the same below.

2 Distillation Ethanol (water): Add enough fresh CAO and then distill.

3 Filter NaCl solution (CaCO3).

4 Sublimation of NaCl (I2) Iodine Kno3 (NH4Cl) is removed by heating

5 Extraction method The bromine element in bromine water is extracted with benzene ccl4.

6 Dissolution method Iron(Al) Add sodium hydroxide solution to dissolve aluminum.

7 Saturated sodium bicarbonate solution for CO2 (SO2) in addition method; Co (CO2) with scorching C

8 Conversion method For example, to separate Fe(OH)3, add sufficient sodium hydroxide solution to remove Al(OH)3 and separate Fe(OH)3

Excess CO2 is then introduced into the sodium tetrahydroxyaluminate solution to convert it to Al(OH)3

FeCl2 (FeCl3) with iron powder; FeCl3 (FeCl2) is introduced into the solution

A false because the mixture formed by alcohol and water is not as simple as you think, the hydrogen bonding between the alcohol molecule and the H2O molecule and other actions make the formation of an azeotropic liquid, that is, the mixture has a certain boiling point, so it cannot be distilled and separated.

b False. The solubility of NaCl decreases though as the temperature decreases.

However, the reduction is too small and basically unchanged, so it cannot be precipitated in large quantities and cannot be separated by the method of cooling hot saturated solution.

NaCl can only evaporate and crystallize.

A false water and alcohol will form an azeotrope, and there will be a fixed boiling point.

B wrong cooling method refers to the solution to a certain temperature, and then gradually cool the method, whether this can be used cooling method, is to see its solubility curve, if the solubility change is larger, you can use the cooling method! However, the solubility of NaCl does not change much, and it is impossible to precipitate it in large quantities by the cooling method.

a.Suppose there are several mung beans in a ** soybean and you are asked to separate the mung beans and soybeans, will you pick up all the beans and put them on another plate? Or pick up a few mung beans and put them on another plate?

This involves the issue of energy use, and while there is nothing wrong with method a, there is a simple way why not use it? Anhydrous copper sulfate should be added.

b."So by the cooling method, I contain a small amount from the hot one...."You're getting your punctuation wrong. This is also wrong, the solubility of NaCl does not change much with temperature, and the method of "evaporating solvent" should be used.

A is wrong, the hydrogen bond between the alcohol molecule and the H2O molecule makes the formation of an azeotrope, that is, the mixture has a certain specific boiling point, so it cannot be distilled and separated. Similarly, a mixture of two liquids with little difference in boiling point cannot be fractionated.

B: The solubility of sodium chloride decreases very little with the decrease of temperature, while the solubility of potassium nitrate increases sharply with the increase of temperature. In order to separate pure NaCl from a concentrated solution of NaCl containing a small amount of KNo3, the solution can only be heated and concentrated to reduce the solvent [water], then a small amount of potassium nitrate can be dissolved in a small amount of water at high temperature, and sodium chloride is precipitated due to exceeding the solubility [the "cooling method" may refer to the method of purification by using the law of solubility with temperature, if in this sense, B is right].

The first one is wrong, because both water and alcohol will volatilize and can not get real alcohol that can be neatly passed through quicklime in the condensation of the remaining gases.

No, because the solubility of NaCl does not change much with temperature, it cannot be used this method.

The cooling method is to cool the solution, so that the solubility of some solutes decreases, causing it to be saturated and precipitated, so that crystals can be obtained.

A: Water and alcohol are azeotropic.

The solubility of NaCl does not change much with temperature.

First, the purpose of washing is missing.

As for why the crystals or residues should be washed, that is, the purpose of washing, the common ones are: Removal of impurities: Removal of soluble impurities on the surface of the crystal.

Increased yield: Wash the residue obtained by filtration and remove as much useful substances as possible such as the target product. Prevent environmental pollution:

If there are some environmentally harmful substances on the surface of the filter residue, such as heavy metal ions or CN-, the residue is often washed in order to prevent environmental pollution.

Second, about the washing reagents.

For what to wash with, we can often use the following: distilled water; Cold water; organic solvents, such as alcohol, acetone, etc.; A saturated solution of the substance. The most commonly used detergent is distilled water, and if you use other detergents, it must have its own "uniqueness".

The use of cold water can appropriately reduce the loss of crystals due to dissolution. The common benefits of washing with organic solvents such as alcohol are: it can reduce the loss of crystals due to dissolution, and can remove soluble impurities and water from the surface; Alcohol is volatile, and crystals are easy to dry.

Note: There are special substances whose solubility decreases with increasing temperature, which can be washed with hot distilled water. The use of a saturated solution of the substance minimizes the losses caused by dissolution.

3. The method of washing in the trembling hall.

The correct way to wash is to let the filtered crystals continue to remain in the filter, add detergent to soak the crystals, let the detergent flow naturally, and repeat 2-3 times. Points to note:

Do not stir during the washing process, because the filter paper is already very wet, and if you stir, it is easy to break the filter paper, so that the crystals will be leached, resulting in crystal loss.

Fourth, about the sign of washing.

For clean signs, physical methods can be used, as well as chemical methods. If the aqueous solution of soluble impurities has color, it can be directly passed through the last washing solution whether there is a color chemical **chemical**, if it is colorless, it means that it has been washed, otherwise it has not been washed; Soluble impurities containing Na+ and K+ can be identified by flame color reaction, so as to judge whether they are washed cleanly; For those that cannot be judged by physical methods, they can be judged by chemical methods. Method:

Take the last wash solution for the experiment.

Washing is mainly to wash away the small amount of solvent adsorbed on the surface of the crystal (solid), because filtration does not completely remove it.

When washing, a small amount of cold solvent (liquid nucleus) is generally used.

Crystals do have to dissolve somewhat, it's inevitable. But the amount lost, which can be ignored, is due to the low amount of solvent and the low temperature. In fact, when crystallization, there is a destruction of the mother liquor, so there must be some substances still in the (saturated) solution, which is already a loss.

In general, this loss is much greater than the loss during washing, which causes crystals to dissolve. In fact, the yield of crystallization is related to the solubility at different temperatures, and it is generally impossible to be 100%.

Washing Trilogy:

Why wash the sediment: The surface of the sediment will absorb the branches and attach ions, so the sediment needs to be washed (whether the sediment or filtrate is needed, the sediment needs to be washed).

How to wash: Add an appropriate amount of distilled water to the funnel and submerge it to allow the water to flow out naturally.

During the precipitation washing process, the precipitate will dissolve a small amount, but through washing, the precipitate is relatively pure, or there is no loss of ions in the filtrate).

Some precipitates with high solubility can be washed with alcohol, etc., to reduce losses.

How to judge that the precipitate is clean: Mengling takes a small amount of the final washing solution and adds appropriate reagents, generally to observe that there is no precipitation, which proves that the original precipitate is clean. For example, the precipitation adsorbs ag+

A solution containing Cl- is added; If the side-attack adsorbs SO42-, the Ba2+ test is added).