Cup of tea. Fun chemistry experience at home

ENTERTAINING EXPERIENCES AT HOME
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A cup of tea. Chemical experiments

Entertaining experiments in chemistry

Entertaining experiences at home / Chemistry experiments for children

After sugar syrup, jam and honey, which we did in previous chaptersnaturally will go to tea. Let's single out a substance from tea that raises vitality and invigorates. We are talking about caffeine (this substance was first found in coffee beans, there is even more of it than in tea leaves).

Strictly speaking, tea contains several tonic substances - vitamins, essential oils, etc. But the leading role belongs to caffeine, from the class of alkaloids (this is an extensive class of nitrogen-containing organic compounds; it also includes nicotine from tobacco, papaverine from poppy, etc.). d.).

For the experiment, you will need a porcelain or metal crucible (you can use any suitable metal vessel, preferably not flat, but tall, like a glass). Put black tea crushed in a mortar - about a teaspoon - and about 2 g of magnesium oxide into it. This substance is sold in pharmacies, usually under the names "burnt magnesia", "magnesium oxide". Mix both substances and put the crucible on fire. Heating should be moderate, not too vigorous. Place a porcelain cup or other similar vessel, such as a jam socket, on top of the crucible or glass, and pour cold water into it. In the presence of magnesium oxide, caffeine will sublimate, i.e., turn into vapor, bypassing the liquid stage. Once on a cold surface, caffeine will return to a solid state and settle at the bottom of a cup or outlet in the form of colorless crystals. Stop heating, carefully remove the cup from the crucible and scrape the crystals into a clean bottle.

But how to make sure that you really have caffeine in front of you? There is a beautiful qualitative reaction for this. Put a few crystals on a porcelain or ceramic plate (a piece of tile will do) and drop one or two drops of concentrated nitric acid. (Concentrated acids must be handled with extreme care!) Heat the plate until the mixture on it is dry. The caffeine will then oxidize and turn into a prominent, orange-colored amino acid.

But that's not all. Let's try to neutralize the acid by adding ten drops of a concentrated ammonia solution to it (not a pharmacy one, but one that is sold in hardware stores). When neutralized, a salt of a very beautiful, red, turning into purple color is formed. Such a salt is called murexide, and the reaction is called murexide.

Further experiments with tea are best done in a chemical cup: they require both good skills and substances that are usually not found at home. We will isolate tannins from tea, and from them we will get tannin, a mixture of substances used for tanning leather (hence the name - tannins), etching fabrics before dyeing, in medicine - as an astringent; remember the astringent taste of strong tea. (Note that for industrial purposes there are other, inedible sources of tannin - ink nuts, or galls, sumac, etc.).

So, we will try to extract tannin from green tea. In the absence of green tea, you can also take black tea, but there are significantly fewer tannins in it.

Pour a small pack of green tea (50 g) in a saucepan with half a glass (100 g) of boiling water and boil over low heat for about an hour to extract the soluble substances as completely as possible. Filter the solution through several layers of gauze or through a cotton cloth folded in half; rinse the sediment on the filter with additional hot water (half a glass). You will receive about a glass of a yellow-green solution.

Add 15-20 g of lead acetate or an appropriate amount of lead lotion to the liquid. Keep in mind that lead acetate should not be ingested: it can cause poisoning. Carefully drain the liquid, add a glass of hot water to the sediment, stir, let stand and drain again. Repeat this operation 3-4 times to remove lead ions. Check if they are really removed by taking a sample of the liquid and adding a few drops of dilute sulfuric acid to it in a test tube. If lead remains, the solution will become cloudy; in this case it is necessary to repeat washing. When the sample is negative, filter the precipitate (this is lead tannate) through glass wool and wash the filter with 50 ml of approximately 1% sulfuric acid solution. After collecting the solution, neutralize the acid by adding dropwise a 0,5% barium hydroxide solution, then filter the precipitated barium sulfate.

The remaining clear solution contains tea tannin. Evaporate it to dryness in a water bath. Scrape off the remaining tannin at the bottom and grind into powder.

Here are some beautiful reactions with tannin (since we don't have much of it, about three grams, we'll spend it prudently).

Dissolve approximately 0,5 g of tannin in 40 ml of water. As soon as you add a solution of iron (III) chloride or another ferric salt, the liquid will immediately turn black. This is ancient ink, only tannin for them was extracted from oak (ink) nuts, growths on leaves and young shoots of oak.

Another striking experience: put about 0,3 g of tannin in a small test tube and drip three drops of concentrated hydrochloric acid. Flobafen is formed - a red substance.

Next, add some tannin to a solution of silver nitrate AgNO₃ (lapis); a lapis pencil from a pharmacy is also suitable. This time, silver tannate will precipitate. He has a brown color.

And the last experience with tannin. In a 2% hydrochloric acid solution, dissolve about 0,3 g of vanillin (or the corresponding amount of vanilla sugar) and add three times less tannin. Raspberry coloring will not be slow to appear. This is a characteristic reaction not only to tannin, but also to substances from the class of catechins in general, to which many tannins belong.

Author: Olgin O.M.

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