An important place in experimental chemistry is demonstration attempts. The observational perception of chemicals and phenomena allows students to master the basic theoretical concepts of chemistry, developing logical thinking, identifying the practical application of chemistry, helping to consolidate knowledge.
The following experiments are available at the School Chemistry Laboratory: beautiful and safe. It describes the process of experimentation and explains what is happening.
In a flat glass bowl (suitable for Petri’s bowl), fill the flour with triethyl ether or freon, add aluminum foam, mix and get the hangover. Take powder as much water as possible to get enough dense waves, but do not overload the dust. Aluminum powder on the surface should be carefully removed with filter paper. Cover the flask with a glass tray (can also be used in a watch glass) and so that the solvent does not rinse, cover the glass cover with an epoxy adhesive.
Put the wrap in the refrigerator for a few minutes, then remove and put on the table. If the tip of the finger touches any side of the tape, almost immediately from that part to the center of the vessel will “run” the silver waves. This phenomenon can be watched for a few seconds until the part of the glass that finger has frozen.
How to explain that phenomenon?
Fiber flow decreases the thickness of the thin layer of the solution adjacent to the vessel wall. The heated fluid rises above and cools rapidly, with the force of gravity replacing the layer with more dense layers of the surrounding solution.
By heating the vessel in different ways, you can create different fluid motion pictures. For example, if we put the pot on the thick books weighing 5 cm from each other and touch the center of its floor, the flow of fluid will remind you of a small splashing source.
While doing this exciting experiment, you must observe some security rules.
You should not heat the pot strongly, as the liquid will begin to vapor quickly and the vapor pressure will be violated. Experience is needed in a room away from the fire and in a ventilated room.
If the vessel is hermetic, it can be kept for a long time and it is always possible to surprise those present with a magnificent view of silver waves.
Reactions to mortality. It is known that some solid substances interact when interfering with the color of the mixture, and occasionally turning off water or gas.
P.M. Isakov, by studying such processes, suggested to heal the reactionary materials and call the reactions “tearing reactions.” Later these reactions were called mechanical chemistry.
Typically, the dry matter has badly interacted, but the powder is absorbed in the air by some or all of the moisture that is complete enough to react.
Mechanic-chemical reactions are very sensitive, resulting in the fact that their materials are concentrated, that is, they are not diluted with a solvent. Only the mortar and the mortar are needed for their implementation. Present the following experiments in which mechanical-chemical reactions are taking place.
1. Add 0.3 g of anhydrous copper sulfate and 0.4 g of yellow blood and cast into the mortar. As a result of the formation of copper diphtheria, the mixture obtains a reddish color.
2CuSO 4 + K 4 [Fe (CN) 6 ] = Cu 2 [Fe (CN) 6 ] + 2K 2 SO 4 :
2. Apply 0.1 g of AgNO 3 in the mortar (can also be a mixture of AgNO 3 (Liquid Pencil) and 0.1 g KJ, which is sold in pharmacies The mixture is yellow, as the yellow silver iodide emerges.
AgNO 3 + KJ = AgJ + KNO 3 :
3. Apply 0.3 g of barley hydroxide and 0.1 g of chromium anhydride. During irrigation, at the expense of water, the dry mixture is gradually cooled and converted into liquid mass.
Ba (OH) 2 + CrO 3 = BaC 2 O 4 + H 2 O:
4. Separate 1.1 g of potassium di-chlorate and 1.5 g of oxalic acid in a mortar, then fill with a glass jar (for good visibility) and mixed with a glass stick, and then a fever reaction will start.
K 2 Cr 2 O 7 + H 2 C 2 O 4 = K [Cr (C 2 O 4 ) 2 ] + H 2 O + CO 2 :
The reaction mixture blends heat up and finally coalesced into a purple mass. The formation of foam is explained by the separated CO 2 gas. The important place in Experimental Chemistry
What’s the odor of the material?
No matter how clear it is, it is not so simple. In general, the smell is due to the presence of many volatile substances in the composition of the substance, one of which forms the smell. For example, garlic odor is due to the alliin in its composition, C 6 H 11 NO 3 S (sulfoxide). such a substance was found in “head” onion.
Now let’s find out what the herring smell of saliva is formed on the basis of the material. To do this, you need to explore the fish salt.
Add a small amount of fish salt to the test, add a dense solution of the same amount of NaOH or Na 2 CO 3 (the environment should be strong).
Close the probe mouth with a tape with a glass tube and heat it up to the boiling point of the alcohol. If we draw the red light make paper near the edge of the glass tube, it will tie. You probably guess why. Now, if we approach the end of the pipe with a damped glass rod, a cloud of white smoke will come and, finally, if it is burned out of the pipe, it will burn with a flammable flame.
If we replace the cork with a pipe cylinder and continue to heat, lower the gas pipe into a solution containing iron (III) chloride solution, then the grayish-reddish sedimentation of Fe (OH) 3 will arise.
After all, one can answer the question: what is the smell of fish stored in salty water?
Due to the fact that there is a problem with protein hydrolysis products with amines, the most commonly contained in diphtheria – and trimethylamines. True, the ammonia will come in the same way, but it will not burn in the air.
The same experience can be done with herring.
Take a small piece of fish separated from the bark instead of a hard, with a mortar with a dead lump to damp wound, and then paste it into the test and perform the experiment in the above manner. We will have the same result.
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A little alchemy
Let’s try to get “gold” from the usual canned box or metal tin without magic.
Tin is one of the oldest known metals (gold, mercury, iron, silver, lead and copper) from ancient times.
Currently, 40% of tin production is used in the production of canned food, so it is called “canned metal”.
You will probably guess that the resulting “gold” will be tin sulfide, SnS 2 , that is, the foil “gold“, that is, the inverted “gold” and is used as a coloring agent.
To perform the experiment is required sulfur, ammonium chloride, and heater, an oven furnace or a closed electric tile.
At first, weigh the 1 box S and 4 scales at the crusher sandwich NH4 Cl, prepare the mixture and move in a fur boat. Put the boat on a tin foil (two split).
To prepare the foil we can melt a few tins and carefully fill it with a cold crusty tile.
Put the boat in the heated oven at 200-220 0 C or on a hot electric tile.
You only have to make an experiment in a trailer. Important place in Experimental Chemistry
Stop an hour later, cool the boat and remove the foil coated with the brown peel. There is little to do with such a “gold”.
Fill the foil with water so that the untreated tin sits on the bottom of the glass, and the yellow solution (finally golden) is transported to another cup, warm up (soak separately), refine and drain. And here we got “gold“, golden yellow SnS2 .
The equation of the reaction is:
2Sn + 2S + 6NH 4 Cl = SnS 2 + (NH 4 ) 2 SnCl 6 + 4NH 3 + 2H 2
If we calculate the ratio of starting materials, then the sulfur and chloride of ammonia are taken with excess, which is deliberate as they can be removed from the reaction medium during heating. This is why the experiment is underway.
1. Скоболев, Чем пахнет селедка, Чимия и жизнь, №5, 1976.
2. N. Paravyan, Reaction in the Stomach, Chemistry, and Life, № 3, 1986.
R. Adamyan, Yerevan State University, “Let’s Amaze”, Naturalist, N2, 2012, pp. 87-89.