Recrystallization operationWhat is used to wash the crystals during the recrystallization process

Generally, the solvent used in the recrystallization process, a small amount, 2-3 times.

Recrystallization. It is the process of dissolving crystals in a solvent or melting, and then recrystallizing them from a solution or melt. Recrystallization allows impurities to be purified or salts that are mixed together separate from each other. Among them it is the result of physicochemical action.

Main steps and purpose of recrystallization:

1) Choose the right solvent.

Purpose: To obtain high purity and yield during recrystallization.

2) The crude product is heated and dissolved with the solvent of choice to make a saturated or near-saturated solution.

Objective: To increase the solubility of the product in solvents.

In turn, the precipitation capacity of the product is increased.

3) Add activated carbon for decolorization;

Objective: To remove insoluble fine particle impurities.

4) Strain while hot.

Objective: To remove insoluble impurities and activated carbon.

5) Cooling. Purpose: Precipitate crystals.

6) Suction filtration. Purpose: To wash the crystals and thus improve the purity of the product.

7) Dry crystals.

Purpose: To remove the solvent and obtain a pure, dry product.

Recrystallization is for purification.

The first crystallization is to remove insoluble impurities and most other impurity ions from the coarse salt. However, it is difficult to remove impurity ions in the coarse salt after only one crystallization, so it is necessary to recrystallize, and in the second crystallization, because the impurity ions have been reduced very low, these ions will be lowered even lower again, so as to purify.

Recrystallization. The general steps are as follows:

1) Choose the right solvent.

2. Dissolution of solid substances, the crude product is heated and dissolved with the selected solvent to make a saturated or nearly saturated solution;

3. Removal of impurities, decolorization with activated carbon;

4. Precipitation of crystals, cooling the filtrate, so that the solution precipitates crystals;

5. The collection and washing of crystals, the crystals are separated from the mother liquor through air filtration, after filtration, open the piston of the safety bottle to stop the filtration, wet the crystals with a small amount of solvent, continue to filter and dry;

7. Drying of crystals, purified crystals can be naturally dried or oven dried according to the actual situation.

The principle of recrystallization.

Solubility of solid organics in solvents.

It is closely related to temperature. Generally, the temperature increases, and the solubility increases. If the solid is dissolved in a hot solvent to reach saturation, the solubility decreases and the solution becomes supersaturated and crystals are precipitated when cooling.

The solubility of the solvent to the purified substance and impurities is different, and the purified substance can be precipitated from the supersaturated solution. And let all or most of the impurities remain in the solution (if the solubility in the solvent is very small, it will be prepared into a saturated solution and then filtered out), so as to achieve the purpose of purification.

I choose ACold water.

Because the precipitated crystals are excavated during the cooling process, the solubility in cold water is very small, so they can be washed in cold water.

If you wash it with a cold solvent, the solvent will stand on the crystal and become an impurity, so it cannot be matched.

Recrystallization is an operation method for separating substances, through dissolution, crystallization, filtration and other steps, to separate a single compound with high purity that needs to be prepared. The following will be described in detail from the operation steps, experimental materials and precautions.

First, the operation steps

1. To prepare the solvent, you first need to select the appropriate solvent, add it to a dry beaker or volumetric flask, and heat it in a water bath until it is completely dissolved. Water, ethanol, xylene, etc. are commonly used.

2. Add the test sample, add the mixture to be separated to the prepared solution, heat and stir to dissolve it completely.

3. Crystallization, while constantly stirring, slowly reduce the temperature to crystallize the substances in the mixture. If there is less crystallization, it can be left to promote crystallization for a period of time, or a small amount of solvent can be added to the solution to induce crystallization.

4. Filtration, filter out the crystals with a funnel and filter paper, wash several times with cold solvent to remove impurities, and then dry or blow dry.

2. Experimental materials and precautions

1. Experimental materials, the main materials required for recrystallization experiments include solvents, substances to be separated, filter paper, funnels, beakers, showers, etc.

2. Precautions, choose the appropriate solvent, and the solubility should be high enough; When adding the sample, it is necessary to avoid adding too much, so as not to affect the purity and yield of crystallization; During the crystallization process, it is necessary to stir evenly so that the crystals are not too small to be captured.

3. The filter paper should be of appropriate size and quality, so as to quickly and evenly adsorb crystalline substances; The drying process should avoid direct sunlight of the ear stall to avoid contamination of the crystals.

Expanding knowledge – recrystallization

Recrystallization is a commonly used chemical experimental operation, which is widely used in organic chemistry, medicinal chemistry and other fields. The principle is to separate the target substances in the mixture by controlling factors such as temperature and solubility to obtain high purity and yield. At the same time, recrystallization is also one of the commonly used experimental methods in scientific research.

The steps are as follows:

1. Prepare the crystals and choose the appropriate solvent.

2. To choose experimental equipment, the first must have a stirring rod, the second is to choose a suitable Ronghe chopstick, and the third is to choose a heater to serve the defense equipment.

3. Put the crystals into the container and then add the slow solution, and stop when the crystals are about to dissolve.

4. Start to heat up the solvent and evaporate part of the solvent. When the solvent evaporates moderately, remove the old and missing crystals of the cooling junction, and the heavy crystals can be obtained.