|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
ENTERTAINING EXPERIENCES AT HOME
Experiments with carbohydrates. Chemical experiments
Entertaining experiences at home / Chemistry experiments for children Carbohydrates are one of the "three pillars" of our diet (the other two are proteins and fats). Glucose and fructose, starch and fiber, dozens of other carbohydrates are continuously formed and "burned" (oxidized) in plant and animal cells, serving as the body's most important energy material. For all the dissimilarity of individual representatives of carbohydrates, they, of course, have common properties that are mandatory for all. This makes it possible to detect carbohydrates even in very small quantities. A true and also beautiful way to recognize them is the Molisch color reaction. Pour about 1 ml of water into a test tube and throw in a few grains of granulated sugar (sucrose), part of a glucose tablet, or a piece of filter paper (fiber). Now add 2-3 drops of an alcohol solution of resorcinol or thymol (these substances are sold in pharmacies). Tilt the tube and carefully pour 1-2 ml of concentrated sulfuric acid down the wall. Be careful with acid, make sure that it does not get on the skin! Fix the test tube in a vertical position. Heavy acid will sink to the bottom, and a bright beautiful ring will appear on its border with water - red, pink or purple. If a substance whose composition is unknown gives such a ring during the Molisch reaction, you can be sure that a carbohydrate is present. Just remember that this reaction is so sensitive that even a speck of dust and a fiber on the walls of the test tube can cause it. Therefore, the dishes in which the reaction is carried out must be washed very carefully, and it is better to rinse with distilled water. Now, having learned to recognize carbohydrates, let's move on to starch, one of the most famous carbohydrates. To begin with, we will learn how to properly prepare starch paste, a colloidal solution of starch in water. Pour some cold water into a saucepan and stir in the starch, at the rate of about two teaspoons per glass (including any water you add later). Stir the mixture well - you get the so-called starchy milk. While stirring, add boiling water to it and, continuing to stir, heat over a fire until until the solution becomes clear. Cool it down. This is the starch paste that sticks paper together so well; therefore it is often used, for example, for gluing wallpaper. You already know that starch turns blue in the presence of free iodine. This property of his is still useful to us; note only that the iodine solution must be very weak. By the way, using such a solution (and to prepare it, it is enough to dilute the pharmacy solution with water), you can examine various food products for starch content. Having prepared a test tube with a weak solution of iodine, we will observe the transformations of starch. Let's try to make glucose from starch paste. Huge molecules of starch under the action of water are hydrolyzed, split into smaller molecules. First, soluble starch is formed, then smaller "stumps" - dextrins, then a disaccharide, but not everyone is familiar with sucrose, and the other is maltose, or malt sugar. Finally, the breakdown of maltose produces glucose, grape sugar. The finished product of hydrolysis often contains all transitional substances; in this form it is known as molasses. To half a glass of starch paste, add 1-2 teaspoons of diluted, approximately 10% sulfuric acid. Do not forget: when diluting sulfuric acid, be sure to pour acid into water, and not vice versa! Set the mixture of paste and acid to boil in a saucepan, gradually adding water as it evaporates. From time to time take samples of the liquid with a spoon and, after cooling slightly, drip dilute iodine solution on them. Starch, as you remember, gives a blue color, but dextrins - red-brown. As for maltose and glucose, they don't color at all. Samples will change color as the hydrolysis progresses, and when the iodine stain disappears, heating can be stopped. However, for a more complete decomposition of maltose, it makes sense to boil the mixture for a few more minutes. After boiling, the liquid should be cooled slightly and gradually add about 10 g of chalk powder to it with stirring in order to completely neutralize sulfuric acid. At the same time, the mixture will foam, because during the reaction of acid with chalk, carbon dioxide is released. As soon as the foaming stops, put the resulting yellowish liquid on a low fire so that it evaporates by about two-thirds, then filter it still hot through several layers of gauze, then evaporate the liquid again, but now more carefully, not over an open fire, but in a water bath (the mixture burns easily). You will get a thick sweet molasses, the basis of which is glucose. In much the same way, molasses is obtained in large quantities at starch factories. Glucose is necessary for a person, it is one of the main suppliers of energy. But bread, potatoes, pasta contain mainly starch, and in the body it turns into glucose under the action of enzymes. In our experiment, sulfuric acid was not consumed during the reaction. She played the role of a catalyst, i.e., a substance that sharply accelerates the course of the reaction. The catalytic action of natural enzymes is much stronger, it is more targeted. There are a lot of enzymes, and each of them has its own, narrow area of \uXNUMXb\uXNUMXbwork. For example, the enzyme amylase contained in saliva can convert the polysaccharide starch into the disaccharide maltose. Let us follow experimentally the action of this enzyme. Rinse your mouth with distilled water (and if it is not available, then boiled) for a minute - you will get a solution of saliva. Filter this solution and mix with an equal amount of starch paste. Place the test tube with the mixture in a glass of warm (about 40 °C) water. Take samples with iodine from time to time - the color change will be exactly the same as hydrolysis with sulfuric acid, but the reaction will go faster. Not later than a quarter of an hour later, starch is hydrolyzed to maltose, and the color reaction with iodine will disappear. There is a very simple experience: try chewing a piece of white bread for a long time. You will notice that its taste becomes sweetish. This is the enzyme amylase that converts the starch in bread into maltose. Author: Olgin O.M.
▪ blowgun
▪ Starch loses its color under the action of sodium sulfite and soda ▪ Semi-permeable partition traps sugar and allows water to pass through
Artificial leather for touch emulation
15.04.2024 Petgugu Global cat litter
15.04.2024 The attractiveness of caring men
14.04.2024
▪ All the chemical ingredients of life found on Enceladus ▪ A hungry microbe will not touch ▪ XTR305 - industrial analog signal driver with diagnostics ▪ Thunder Power electric car with a range of up to 600 km
▪ section of the Electrician website. PTE. Article selection ▪ article Features of labor activity of women and teenagers. Basics of safe life ▪ article How many crocuses do you need to collect to get a kilogram of saffron? Detailed answer ▪ article Creeping wheatgrass. Legends, cultivation, methods of application ▪ article Power Amplifiers. Part two. Encyclopedia of radio electronics and electrical engineering ▪ article Frying pan (pan) for a pigeon. Focus Secret
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
We recommend interesting experiments in physics:
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page