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CUP OF TEA

 

After the sugar syrup, jam and honey, which we studied in the previous lesson, will naturally go to tea. Select from the tea substance that raises vitality and invigorates. It comes to caffeine (this substance was first found in coffee beans, it is even more than in tea leaves).

Strictly speaking, in the case there are several restorative materials - vitamins, essential oils, etc. But the leading role belongs to the caffeine from the class of alkaloids (a wide class of nitrogen-containing organic compounds; it also includes nicotine from tobacco, papaverine from poppy, and so on).

For an experience you will need a porcelain or metal crucible (you can use any suitable metal container, preferably flat and high, like a Cup). It lay crushed in a mortar black tea - about a teaspoon - and about 2 g of magnesium oxide. This substance is sold in pharmacies, usually under the names of "burnt magnesia, magnesium oxide". Mix both substances and place the crucible on the fire. The heat should be moderate, not too energetic. On the top of the crucible or Cup, put a porcelain Cup or similar receptacle, such as receptacle for boiling, and pour cold water. In the presence of magnesium oxide caffeine will waggonette, i.e., to turn into vapor, bypassing the stage of the liquid. Getting on the cold surface, the caffeine will once again return to the solid state and will settle on the bottom of the Cup or socket in the form of colorless crystals. Stop heating, carefully remove the Cup from the pot and scrape the crystals in a clean flask.

And how do you make sure that you are really the caffeine? This is a beautiful quality response. A few crystals put on a porcelain or ceramic plate (will fit a piece of tile) and drip one or two drops of concentrated nitric acid. (With concentrated acid must be handled with extreme caution!) Heat the plate up until the mixture it will not become dry. Caffeine will oxidize and turn into noticeable, orange, Malinovo acid.

But this is not all. Let's try to neutralize the acid, add ten drops of concentrated ammonia solution (not drugstore, but the one that is sold in hardware stores). When neutralization is formed salt is very beautiful, red, rolling in purple color. This salt is called murexide, and the reaction - murexide.

Further experiments with tea it is better to put in chemical circle: they require good skills, and such substances, which the house usually does not happen. We will select from the tea tannins are tanida, and one of them will get tannin, mixture of substances, used for tanning leather (hence the name - tanning agents), treatment of fabrics before dyeing, in medicine as an astringent; remember astringent taste of strong tea. (Note that for industrial purposes there are other, non-edible sources of tannin - ink nuts, or galls, sumach, and so on).

So, we will try to extract tannin from green tea. If no green you can take and black tea, but it tandav significantly less.

A small bundle of green tea (50 g) pour into a saucepan with one-half Cup (100 g) of boiling water and boil on low heat for about an hour to as much as possible to extraction of soluble substances. The solution, filter through several layers of cheesecloth or through a cotton cloth, folded in half; the precipitate on the filter additionally rinse with hot water (half a Cup). You will get about a glass of yellow-green solution.

Add the liquid 15-20 g of lead acetate or the corresponding quantity of lead lotions. Keep in mind that the lead acetate should not get in the mouth: it can cause poisoning. Carefully pour off the liquid, to the precipitate, add a glass of hot water, stir, let sit and drain in Nov. Repeat this 3-4 times to remove lead ions. Check whether they are removed by taking a fluid sample and adding to it in the test tube a few drops of diluted sulphuric acid. If the lead remained, the solution is turbid; in this case, you need to repeat the washing. When the sample is negative, filter the precipitate (this is tannat lead) through glass wool and filter rinse with 50 ml of approximately 1%-aqueous solution of sulfuric acid. Collecting the solution, neutralize the acid by adding dropwise a 0.5%solution of barium hydroxide, and then filter the precipitation of barium sulfate.

The remaining clear solution contains tea tannin. ApARTe him to dryness on a water bath. Remaining at the bottom of tannin scrape and grind into powder.

Here are some beautiful reaction with tannin (since we have it a bit, gram three, we will spend it prudently).

Approximately 0.5 g of tannin dissolved in 40 ml of water. As soon as you add a solution of ferric chloride (III) or other salts of trivalent iron, the liquid will immediately turn black. This is an old ink, only tannin for them was obtained from oak (ink) nuts (Gauls), growths on the leaves and young shoots of oak.

Another good experience: about 0.3 g of tannin put in a small test tube and drip three drops of concentrated hydrochloric acid. Develops phlobaphene - red substance.

Next, add a bit of tannin to a solution of silver nitrate AgNO3 (silver nitrate); good and lyapisny pencil from the pharmacy. This time will drop precipitate tannate silver. He has a brown color.

And last experience with tannin. A 2%solution of hydrochloric acid dissolve about 0.3 g of vanillin (or a corresponding amount of vanilla sugar) and add three times less tannin. Crimson staining will not be slow to appear. This is a typical reaction not only in tannin, but generally the substances from the class of catechins belong to many tannins.

O. Holguín. "Experiments without explosions"
M., "Chemistry", 1986

 

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2011-12-04 08:52:12
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