Which substances are separated by distillation and which are crystallized? What recrystallization?

Alcohol, distilled water, etc. need to be separated by distillation, and sodium chloride and potassium chloride need to be separated by crystallization.

Distillation: It is a common method for separating two or more liquids with large differences in boiling point, the molecules of the liquid have a tendency to escape from the surface due to molecular movement, and this tendency increases with the increase of temperature, that is, the liquid has a certain vapor pressure at a certain temperature, and when its temperature reaches the boiling point, that is, the vapor pressure of the liquid is equal to the external pressure (reaching the saturated vapor pressure) There are a large number of bubbles escaping from the inside of the liquid, that is, the liquid boils.

Crystallization method: An operation method that uses the crystallization method to separate the differences in the solubility of each component in the mixture in the same solvent or the significant difference in solubility under the condition of cold and heat.

As long as there are crystals formed, it indicates that the purity of the compound has reached a considerable purity. Crystallization is one of the important methods for refining solid compounds. The crystals that are precipitated for the first time are often impure, and the process of processing the impure crystals into purer crystals is called recrystallization.

Distillation is the process of obtaining a liquid from a mixture of liquids, such as alcohol, distilled water, ......

Crystallization is the solid mixture to obtain some kind of solid, such as: kclo3, NaCl......

Recrystallization is an operational step that is used after crystallization, but when the purity of the object is not high.

Distillation is not the same temperature. Extraction is the extraction of carbon tetrachloride from iodine. Liquid separation is two substances that are immiscible with each other, and precipitation is solid to liquid.

Crystallization, the mixture is made into a hot saturated solution, because the solubility of potassium nitrate changes with temperature is obvious, and the solubility of sodium chloride changes with temperature changes very little, and then the hot saturated solution is cooled and crystallized. Most of the precipitation is potassium nitrate, and if it is to be purified, it is recrystallization, and the precipitated part will be made into a hot saturated solution and then cooled. After many times, purer potassium nitrate is obtained.

If evaporation crystallization is selected in the purification of the mixture, because the impurity content is small, the saturation cannot be reached, so the two substances will not crystallize and precipitate at the same time.

Mixture crystallization purification, generally the content of the two substances is very different, for example, a content of more than 95%, through evaporation, cooling crystallization, so that the high content of the substance crystallization, and 5% of the impurities because of unsaturated and left in the solution, so as to achieve the purpose of purification.

Or the solubility of the two substances is very different, such as potassium chloride.

and sodium nitrate to prepare potassium nitrate.

Because the solubility of potassium nitrate increases rapidly with temperature, while sodium chloride.

The solubility is very insensitive to temperature, through evaporation, sodium chloride is the first to crystallize in the hot solution, and the separated solution continues to cool and crystallize to obtain relatively pure potassium nitrate.

If the solubility of the two substances is close and the content is also similar, there is no way to purify it by evaporation crystallization.

No, the solubility of the substances used by evaporation crystallization varies greatly with temperature, and its temperature is raised to precipitate crystals for further separation and purification.

This is not the case, since there are two substances in the mixture, their solubility is not the same. It can be controlled at a certain temperature to dry and precipitate.

Normal is still thereThe solubility is small and crystallizes first.

Absolutely:Separating solutes by evaporation crystallization will never be burned dry！Be sure to find a way to keep the volume under control of the other solute unsaturated.

These three are still very different.

Extraction is generally used to separate two immiscible liquids, which are operated by a separating funnel;

Distillation is commonly used to separate miscible liquids with large differences in boiling points, and the instruments are distillation flasks, condenser tubes, receiving bottles, etc.;

Recrystallization is used to separate solid mixtures and use solubility differences to purify solids, generally requiring heated instruments, funnels, glass rods, etc.

Extraction is based on the solubility of two different solvents to the same solute, and then the solute in the solvent with low solubility is extracted by the solvent with high solubility.

Distillation is the process of heating a substance to its boiling point and then evaporating, which is called distillation.

Recrystallization is when the temperature of the substance is below the melting point or saturated in the solvent, and then it will re-precipitate and become crystalline.

"Crystallization" refers to the first crystallization, that is, when a compound is prepared from a solution, the solvent is evaporated by heating and then cooling, so that the target substance is first crystallized and precipitated from the solution, and then filtered to prepare the compound.

"Recrystallization" means that the compound prepared by the first crystallization is not pure, continues to dissolve and recrystallizes out of the solution, at this time, because the amount of impurities is much smaller than that of the target substance compared with the first preparation, the impurities will not precipitate, so it plays a role in purifying the target compound.

However, recrystallization will cause the loss of the target substance, especially the solubility is larger, so it is necessary to evaporate the solution as much as possible to reduce this loss, but the problem is that the impurities may reach saturation again, even if it is not saturated, the concentration will become larger, so that when filtering, the solution containing very concentrated impurities will be adsorbed on the crystallization of the target substance, so a recrystallization can not make the target compound very pure, so it is necessary to continue to recrystallize twice, tertiorily, or even more times, once per recrystallization, It was purified once.

The recrystallization method is suitable for purifying substances with small solubility at low temperature and significantly increased with increasing temperature. When the temperature of the hot solution gradually decreases, the solubility of the target substances dissolved in the solution drops sharply and a large amount of precipitation is released, while the impurities are generally substances that still have a large solubility at low temperatures (even if they are not, they will not reach saturation and precipitate due to the small amount in the recrystallization process).

Recrystallization, that is, repeated crystallization, is a general term.

Cooling crystallization is a method in crystallization, that is, heating to obtain a hot saturated solution first, and then cooling, in the process of cooling, the solubility of the solute decreases, so the crystallization is precipitated, and it is generally suitable for large changes in solubility with temperature, such as kno3.

Evaporation crystallization, that is, direct heating to evaporate the solvent, that is, to obtain solute crystals, is generally suitable for substances whose solubility does not change much with temperature, and will not decompose stable properties during the heating process, such as NaCl.

Evaporation crystallization without crystal water, whereas cooling crystallization with crystal water.

1. Evaporation crystallization and evaporation are obviously not the same concept, but only some of the functions overlap; Evaporation is the operation of removing the solvent, which can only remove a small part of the solvent, which is equivalent to concentration and not necessarily crystallization; Evaporation crystallization, on the other hand, must remove the solvent until a large amount of crystals have precipitated.

Evaporation crystallization: Qingheng removes part of the solvent by temperature in order to turn the unsaturated solution into a supersaturated solution, thereby precipitating crystals.

Cooling crystallization: Crystals are precipitated by reducing solubility (without removing solvents) by cooling the solution into a supersaturated solution.

After crystallization, it is only separated by two states: solid and liquid.

Recrystallization refers to the re-dissolution of the crystals obtained after the initial crystallization with a solvent and then crystallizing the solute, the purpose is to remove the impurities entrained during the initial crystallization, that is, to play a purification role.

2. Dissolved in dilute nitric acid obviously refers to the reaction of bright eggplant with dilute nitric acid to form a solution;

Soluble in water includes two functions: (1) it reacts with water and dissolves in water; (2) Physical dissolution with water.

The reason why dilute nitric acid is used instead of dilute hydrochloric acid is often because Cl(-) reacts, and if Cl(-) does not react, then dilute hydrochloric acid can completely replace dilute nitric acid.

3. Fe (2+): light green; fe(3+): light purple, but often yellow due to hydrolysis; cu(2+): Blue.

4. Dialysis refers to the purification method of removing certain impurities by the membrane action of the honor bond; Salting out refers to the method of precipitating a certain component by adding electrolyte, which is used for separation; If you see the concept clearly, you will know that the difference is **.

5. The separation and purification generally used in middle schools are as follows:

Separation of solids and liquids: filtration, centrifugal precipitation;

Liquid-to-liquid separation: extraction of immiscible liquids; The miscible liquid is evaporated.

Purification methods: evaporation, crystallization, sublimation, condensation, etc.