The experimental method Shanghai Hengyuan brought to friends today is recrystallization and filtration. The purpose of this experiment is to learn the principles and methods of purifying solid organic compounds by recrystallization, as well as to grasp the methods of suction filtration and thermal filtration operations.
The solubility of solid organics in solvents generally increases with increasing temperature. If the solid is dissolved in a hot solvent to reach saturation, the solution becomes supersaturated and crystals are precipitated due to the reduced solubility during cooling. The difference in solubility of the purified substances and impurities using solvents can cause the purified substances to precipitate out of the saturated solution while leaving all or most of the impurities in the solution to achieve the purpose of purification.
The general process of recrystallization:
1. Dissolve the substance to be recrystallized in a suitable solvent at a higher temperature;
2. Filter while hot to remove insoluble materials and colored impurities;
3. The filtrate is cooled so that the crystals are precipitated from the supersaturated solution, while the soluble impurities remain in the solution, and then filtered under reduced pressure to separate the crystals from the mother liquor;
4. Wash the crystals to remove the attached mother liquor;
5. Dry crystallization.
Experimental steps:
1. Weigh 3.0g of crude acetanilide into a 250mL Erlenmeyer flask;
2. Add 100mL of water, install a reflux condenser, heat to boiling, keep boiling for 2-3min;
3. Take off slightly cold, add 0.2g activated carbon, and then heat for 5-10min;
4. Use the hot funnel to filter while hot, and the filtrate is received with a clean 200mL beaker;
5. Static and natural cooling. After full crystallization of acetanilide, perform cold decompression filtration to compact the filter cake.
6. Drain the water thoroughly, dry and weigh.
You need to pay attention to during the experiment:
1. When adding 20% ​​water, add activated carbon together.
2. During hot filtration, the water in the insulation funnel must be as hot as possible and move quickly.
3. The pressure-reducing filter paper must be wetted in advance, and the pressure-reducing filter paper cannot be decompressed too much after laying. Before pouring the filtrate, the filter paper should be close to the bottom of the funnel to prevent the filter paper from being pressed through.
4. If the filtrate has been cooled to room temperature, there is still no crystallization after a long time of rest, you can stir it with a glass rod.
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