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ENTERTAINING EXPERIENCES AT HOME
Man-made fibre. Chemical experiments
Entertaining experiences at home / Chemistry experiments for children In recent decades, chemical fibers have literally conquered the world. And although cotton and flax are still sown, sheep and goats are bred, even artificial and synthetic fibers are added to traditional natural fibers to give strength, elegance, crease resistance and other useful properties. Finally, to conserve natural fibers... To prepare on your own the most common now chemical fibers - polyamide (such as nylon) and polyester (such as lavsan) will, perhaps, be difficult. Let's stop the choice on a copper-ammonia fiber. This is one of the very first artificial fibers, the raw material for it is cellulose, for example, from sawdust and other waste from the forestry industry. Copper-ammonia fiber is also used now - in carpet weaving, at knitting factories, but much less often than before, because more durable and cheaper fibers have appeared. However, for an independent experiment, it is probably not possible to find a more convenient object.
Artificial fibers are formed from viscous spinning solutions, forcing them through narrow holes - spinnerets. In this case, the dissolved fiber is released in the form of threads. In our case, the basis of the solution is a compound of copper with ammonia, which has the general formula [Сu(NH3)n)(HE)2. To prepare such a solution, first of all, stock up on basic copper carbonate Cu (OH)2CO3. If there is no ready-made salt, prepare it in the simplest way - drain the aqueous solutions of copper sulfate and soda ash, filter the precipitate and dry it. In a bottle with a narrow neck, pour 20 ml of a 25% ammonia solution (it is better to do this under draft or in fresh air) and add 2 g of basic copper carbonate. After closing the bottle with a rubber stopper, shake the mixture to get a dark blue homogeneous liquid. This is a copper ammonia solution. It has a very important property: it is able to dissolve cellulose (fiber). Pick up rubber stoppers to two small flasks and pour a dark blue solution into these flasks. Throw small pieces of pharmacy cotton wool into one; throwing another portion of cotton wool, close the bottle with a cork and shake the contents. In the second flask, in the same way, in small pieces, dissolve white blotting or filter paper. In both cases, viscous solutions should be obtained, resembling syrup in density. Of these, fiber can be distinguished, which is the basis of the fiber. To make sure of this, pour diluted vinegar into a glass and add any of the spinning solutions drop by drop. Fiber flakes will precipitate. However, yarn cannot be made from flakes. How to get a thread from a solution? Just like at a factory - by forcing the solution through a narrow hole, and into a solution of sulfuric acid - the shape of the thread is fixed in it. To see how this happens, put the following experiment: into a glass with a 10% solution of sulfuric acid, drop a copper-ammonia solution of cotton wool or blotting paper from a pipette. Part of the solution will sink to the bottom, leaving behind a shiny thread. Try to grab this thread with tweezers and carefully pull it out of the glass. This is the real copper-ammonia fiber. True, the thread turned out to be not very even. But we'll fix it. Only two people need to set up the experiment: one will mold the thread, and the other will extract it from the solution. Insert the needle from the medical syringe as tightly as possible into the thick-walled rubber tube. Pour the spinning solution into the tube, close it with a cork and immerse the needle in a bath or cuvette with a solution of sulfuric acid. Your friend should stand with tweezers at the ready: you will gradually squeeze the tube, and he will pick up the formed thread with tweezers and stretch it through the solution poured into the bath. Such an experience after a little training usually works out well. For convenience, try winding the resulting thread onto a spool. Instead of a rubber tube, you can take a large syringe or an old bicycle pump. Both viscose and acetate fibers are obtained in much the same way, only other solvents for fiber are taken. In all cases, its molecules are arranged in such a way that an oriented thread is formed. From the thread you received, it is probably not possible to weave a handkerchief. But we did not strive for this. You saw with your own eyes how a beautiful silk thread turned out from nondescript paper dissolved in a dark blue liquid. Author: Olgin O.M.
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