Purification of crude salt. Experimental purpose 1. Master the operation skills of dissolution, filtration, evaporation and other experiments. 2. Understand the chemical principle of separating mixtures by filtration. 3. The application of experiential filtering principle in social practice such as life and production. 2. Experimental instruments and medicines: crude salt, BaCl2, NaOH, Na2CO3, water equipment: beaker, glass rod and medicine spoon. Rubber tip dropper, filter paper, match three. Experimental principle The raw salt contains insoluble impurities such as sediment and soluble impurities such as sulfate, MgCl2 and CaCl2. Insoluble impurities can be removed by dissolution and filtration, and soluble impurities can be converted into precipitate or gas by adding appropriate drugs. Four. Experimental operation 1) Remove insoluble impurities 1. Dissolve a proper amount of distilled water and pour it into a beaker. Use drugs. 2. Filter and take a piece of filter paper, fold it in half twice, open it into a cone shape, put it into a glass funnel, moisten it with distilled water, flatten it with a glass rod, and make the filter paper cling to the funnel wall without bubbles in the middle. Place the funnel on the iron ring of the armored platform so that the nozzle at the lower end of the funnel is close to the inner wall of the beaker. Gently lean the glass rod on the three layers of filter paper in the funnel, and the mouth of the beaker is close to the glass rod, so that the liquid can flow down the river. After filtration, wash the filter residue with a small amount of distilled water for two or three times. Carefully observe the residue on the filter paper and the color of the filtrate. When the filtrate is still turbid, it should be filtered again. If the filtrate is still turbid after two times of filtration, the experimental device should be checked and the reasons should be analyzed, such as the damaged filter paper, the liquid level in the funnel is higher than the edge of the filter paper during filtration, and the instrument is unclean. After finding out the reason, the operation should be repeated. 3. Evaporate the obtained clear filtrate into an evaporating dish along the glass rod. Put the evaporating dish on the iron ring of the iron frame. Heat with an alcohol lamp. The filtrate was continuously stirred with a glass rod during heating. When a large number of solids appear in the evaporating dish, stop heating, and use the waste heat of the evaporating dish to evaporate the filtrate. 2) remove soluble impurities 1. Put the evaporated crystal into a test tube with a dissolving spoon, add distilled water, and shake well to completely dissolve it. (Impurities at this time: sulfate ion, magnesium ion, calcium ion) 2. Remove sulfate, add excessive BaCl2 solution into the test tube with rubber dropper, shake well, and a large amount of white precipitate is generated, and filter. (Impurities at this time: barium ion, magnesium ion, calcium ion) 3. Remove barium ions and calcium ions, pour the filtered filtrate into a test tube, add excessive Na2CO3 solution into the test tube with a rubber dropper, shake well to produce a large amount of white precipitate, and filter. (Impurities at this time: magnesium ions, carbonate ions) 4. Remove magnesium ions, pour the filtered filtrate into a test tube, add excessive NaOH solution into the test tube with a rubber dropper, oscillate to produce a large number of white precipitates, and filter. (Impurities at this time: hydroxide ions and carbonate ions) 5. Removing hydroxide ions and carbonate ions, pouring the filtered filtrate into a test tube, adding excessive dilute hydrochloric acid into the test tube with a rubber dropper, and oscillating to generate gas. (Impurity at this time: dilute hydrochloric acid) 6. Evaporation v. experimental summary