Filter paper, scissors, matches and pieces of paper. Experimental principle Raw salt contains insoluble impurities such as sediment and soluble impurities such as:. Insoluble impurities can be dissolved and filtered.
Taking out, and then evaporating water to obtain pure refined salt. Fourth, the experimental operation 1. Weigh 5g of raw salt (accurate to 0. 1g) with a tray balance and dissolve it. Measure 10ml of water with a measuring cylinder and pour it into a beaker. Add a spoonful of crude salt to the water with a medicine spoon and observe the phenomenon. Stir with a glass rod and observe the phenomenon (glass rod). Then add the original salt and stir with a glass rod until the original salt is no longer dissolved. Observe whether the solution is turbid. Weigh the remaining raw salt on the balance and calculate how many grams of raw salt are dissolved in 10 ml of water.
2. Filter according to the method described in basic operation 6 of chemical experiment. 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, check the experimental device and analyze the reasons. For example, if the filter paper is damaged, the liquid level in the funnel is higher than the edge of the filter paper when filtering, and the instrument does not.
Cleaning, etc. After finding out the reason, re-operate. 3. Evaporation: pour the clarified filtrate into an evaporating dish. Place the evaporating dish on the iron ring of the iron frame and heat it with alcohol lamp (Figure 20). At the same time, the filtrate was continuously stirred with a glass rod.
When a large number of solids appear in the evaporating dish, stop heating. Evaporating the filtrate by using the waste heat of the evaporating dish.
4. Transfer the solid to the paper with a glass rod, weigh it and recycle it to the container designated by the teacher. Compare the salt state before and after purification, and calculate the refined salt output.
Experimental summary of verb (abbreviation of verb)
Analysis of Problems in Filtering Operation
Filtration is the most commonly used experimental operation to separate liquid from solid. The current junior high school chemistry textbook only briefly introduces the main points of filtration, but in the actual operation process, many details are often encountered. The author talks about his own solutions to the problems often encountered in filtering operation for reference only. (1) How to choose a funnel and filter paper? The size of the funnel mainly depends on the amount of precipitate or precipitated solid to be filtered, rather than the volume of liquid. If there are many sediments or solids, the funnel is large, and vice versa. The cone angle of the funnel should be 60. Proper pipe diameter, too thick to retain water column and too long filtration time. The end of the pipe diameter should be slightly inclined. The choice of filter paper depends on the experiment done. Qualitative filter paper and quantitative filter paper. Quantitative filter paper is mainly used for quantitative analysis of substances. In middle school experiments, qualitative experiments often use filtration operation, so qualitative filter paper is often used. After the selected filter paper is put into the funnel, the edge of the paper is about 5 mm lower than that of the funnel. (2) How to assemble the filter? First, fold the selected filter paper twice, and the second folding should not completely coincide with the folding seam of the first folding. When such a filter paper is put into a funnel (the vertex angle is 60), there is a certain gap between its sharp corner and the funnel wall, but its upper part can be perfectly attached to the funnel wall. The filter installed in this way is faster than the filter with all surfaces stuck to the funnel. When folding, don't press the folding seam at the top corner of the filter paper too flat. So as not to weaken the strength of the tip. Then cut off the small corners of the two layers on the other side of the three-layer paper, so that the upper part of the filter paper can be closely attached to the funnel wall after wetting. Secondly, put the folded filter paper into a suitable funnel, wet the filter paper with bottle washing water, and gently press the upper part of the filter paper on the funnel wall with your fingers. When filling the funnel with water, the funnel neck should be filled with water, or the end of the funnel neck should be blocked with fingers. When filtering, the glass rod faces the mouth of the beaker containing filtrate; The end of the glass rod is close to the three layers of filter paper in the funnel, but it cannot touch the filter paper; Keep it vertical (I think the glass rod inclines and the filtrate overflows); The tip of the funnel neck is close to the inner wall of the beaker mouth for receiving filtrate. The liquid transferred each time should not exceed two-thirds of the height of the filter paper, so as to avoid the filtrate flowing out of the pipe wall without passing through the filter paper. For the liquid and solid substances remaining in the beaker, they should be moistened with solvent or distilled water according to the principle of several times, and all the washing liquid should be transferred to the funnel for filtration. (4) How to clean the sediment correctly? If the sediment needs to be washed, it should be washed immediately, otherwise the sediment will crack or agglomerate if it is placed on the filter paper for too long, and it is not easy to get wet. It can be wetted with original solvent, distilled water or other suitable cleaning agents. Replace the beaker that originally received the filtrate with a clean empty beaker to avoid re-filtering a large amount of liquid because the sediment penetrated the filter paper. The amount of washing liquid should be appropriate, and the collected sediment should be submerged every time. When washing, carefully wash the surrounding sediments from top to bottom with a small amount of lotion and wash them to the bottom of the funnel. Don't make the liquid flow too fast, otherwise the sediment will be washed out of the filter. Don't stir the material in the funnel with a glass rod, so as not to cut the filter paper. All previous efforts are in vain. Generally, you can wash it for about 2 to 3 times, and you can basically wash it (5). How to check whether the sediment has been washed? According to the types of impurities that may be detected on the sediment, appropriate reagents can be added to the last eluate to check the washing degree. For example, when the mixture of Na2SO4 and BaCl2 is filtered after the complete reaction, in order to check whether the precipitate is washed, AgNO3 solution should be selected. If AgCl is not generated by adding AgNO3 solution to the last eluent, it means that the precipitate has been cleaned. (6) When filtering, there is too much filtrate. Funnel and filter paper can be washed with a small amount of original solvent for 2 ~ 3 times, and the original filtrate and washing liquid can be filtered again. (7) Is it necessary to use filtration operation to separate precipitate from liquid? No, when the amount of separated sediment is small, it can be put into a centrifugal test tube and separated by a centrifuge at room temperature. The supernatant of the sediment can be sucked through a straw. If necessary, it can be washed and then centrifuged. Only when the amount of precipitation is large, it is suitable for separation by filtration. (8) Are there any other filtering methods? Yes In order to make the filtration fast and convenient for washing, the Buchner funnel can be used for vacuum filtration, which makes the filtration and washing less time-consuming and convenient for washing. When the filtration needs to be carried out at a certain temperature, the insulation funnel should be used for filtration.