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ENTERTAINING EXPERIENCES AT HOME
Protein experiments. Chemical experiments
Entertaining experiences at home / Chemistry experiments for children The first experience is a qualitative reaction to a protein, that is, such a reaction that will allow us to confidently judge whether the protein is in front of us or not. There are several such reactions. The one we'll spend is called biuret. For it, we need solutions of washing soda (or caustic soda) and copper sulfate. Prepare several solutions that as can be expected to contain protein. Let it be meat or fish broth (preferably strained through gauze), a decoction of some vegetables or mushrooms, etc. Pour the solutions into test tubes about halfway. Then add a little alkali solution - caustic soda or washing soda (it is advisable to boil the soda solution and cool it). Finally, add the blue copper sulfate solution. If there is indeed protein in the test broth, then the color will immediately turn purple. Such reactions are said to be characteristic. They go only if there really is protein in the solution. For control, put an experiment with lemonade or mineral water. Everyone knows that when heated, the protein coagulates and passes into an insoluble form - a raw egg becomes steep. This phenomenon is called protein denaturation. Every housewife knows: to prepare a delicious broth, you need to put chopped meat in cold water. And when they want to cook boiled meat, then large pieces are dipped in boiling water. Does it have a chemical meaning? Let's try to figure it out. Pour a test tube of cold water into it, dip some raw minced meat into it and heat it up. As it heats up, gray flakes form (and in large quantities). This is a curdled protein, foam, which is removed with a slotted spoon so as not to spoil the look and taste of the broth. With further heating, water-soluble substances gradually pass from the meat into solution. These substances are called extractives because they are extracted from the meat when it is extracted with boiling water (in other words, when boiling the broth). First of all, they give the broth a characteristic taste. And meat, having lost these substances, becomes less tasty. Boil water in another test tube in advance and put the raw meat in boiling water already. As soon as the meat comes into contact with water, it will instantly turn gray, but very few flakes form. The protein that was on the surface, under the influence of high temperature, immediately curled up and clogged the numerous pores that permeate the meat. Extractive substances, including proteins, can no longer go into solution. This means that they remain inside the meat, giving it a good taste and aroma. And the broth, of course, turns out a little worse. Protein denatures, coagulates not only when heated. Pour a little fresh milk into a test tube and add one or two drops of vinegar or citric acid solution. Milk immediately turns sour, forming white flakes. It coagulates milk protein. By the way, without such a reaction, you cannot cook cottage cheese, and it is no coincidence that cottage cheese is so useful - almost all milk protein passes into it. When milk is left in a warm place, its protein also coagulates, but for a different reason - lactic acid bacteria work. There are a lot of them, and they all produce lactic acid, even if they do not eat milk, but, say, cabbage juice. Filter some sour milk and add a few drops of some homemade indicator to the whey. The color of the indicator will show that there is acid in the solution. This acid is lactic, it can also be found in cabbage and cucumber pickles. The composition of some protein molecules includes, in addition to carbon, hydrogen, oxygen and nitrogen, also sulfur. This can be verified by experience. Place a little egg white in a test tube with a solution of caustic soda or washing soda and, heating the test tube, add a little solution of basic lead acetate Pb (CH3SOO)2*3H2O-lead lotion, which is sold in pharmacies. If the contents of the test tube turn black, then there is sulfur: this is lead sulfide PbS, a black substance. And in conclusion, let's prepare a real protein glue - casein, which is still used today, despite the abundance of synthetic glues. Casein is the basis of cottage cheese, and if so, then we will make glue from milk, more precisely, from its protein substances. Filter the curd from the whey. What remains on the filter, rinse several times with water to remove soluble impurities, and dry. Then rinse the resulting mass with gasoline and dry again; this is necessary in order to get rid of milk fat (it dissolves in gasoline). When the mass becomes completely dry, grind it in a mortar and mortar - you will get casein powder. Making glue out of it is quite simple - mix the powder with ammonia and water in a ratio of 1: 1: 3. Of course, you will want to test the glue. Try gluing some wooden or ceramic objects with it, because casein glue is especially good for these materials. Author: Olgin O.M.
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