Why does adding green alum to tea turn black

The green alum has a chemical reaction with the tannic acid in the tea to form ferrous tannin, and the tea turns black.

Alum is a natural mineral and is a traditional Chinese medicine. Green alum, also known as ferrous sulfate heptahydrate, iron alum, its refined products are light blue green sandy crystals. The chemical name is ferrous sulfate.

Alum is a chemical substance, is ferrous sulfate crystals, English name: ferrous sulfate, is a columnar or granular aggregate, irregular block. Blue-green, green with streaks white.

The molecular weight is , the pH is 3, and the melting point is 64 degrees Celsius.

Strong thermal decomposition dissolves in water and glycerol.

Insoluble in ethanol.

Alum is a natural mineral and is a traditional Chinese medicine. Its chemical name is ferrous sulfate, ferrous sulfate and tannic acid in the tea have a chemical reaction to produce ferrous tannic acid, and the tea becomes black; Oxalic acid is extracted from rhubarb and other plants, the chemical name is adipic acid, soluble in water, has strong reducing properties, after putting oxalic acid into the cup, the tea that has changed color is restored back to its original color. Because these two substances are small in size and easy to hide, they are used for different purposes.

There is nothing wrong with these two substances, and the gods and men use them to deceive people and deceive people with money; Magicians use it to perform magic tricks, enriching people's spiritual and cultural life. Just as there is nothing wrong with science, some people use it for the benefit of mankind, and some people use it to wage war.

Tea contains a lot of tea polyphenols.

When tea polyphenols encounter divalent ferrous ions, they will react quickly, its properties are very unstable, and they are quickly oxidized to form green-black compounds, so that the tea becomes black.

Tea polyphenols are the general name of polyphenols in tea, which is a white amorphous powder, soluble in water and soluble in ethanol.

Methanol, acetone.

Ethyl acetate, insoluble in chloroform. It has good heat resistance, hygroscopicity, stability at pH 2 7, and easy oxidation polymerization under light or pH 8. It can be combined with iron ions to form greenish-black compounds.

Application of tea polyphenols.

1. Used as an antioxidant.

Tea polyphenols are used as antioxidants because tea polyphenols mostly contain more than 2 ortho-hydroxyl polyphenols and have a strong hydrogen supply capacity, so they are an ideal antioxidant. 4 main catechins.

, the antioxidant capacity was manifested as EGC> EGC>ECG>EC.

2. Used as a food preservative.

Tea polyphenols have inhibitory activity against nearly 100 kinds of bacteria in nature, showing a broad spectrum of antibacterial, and are good food preservatives. As a preservative, tea polyphenols can slow down the biochemical activities of fruits and vegetables after harvest, and delay their later ripening period.

3. It is used as a food color preservation agent.

The oxidation of homopigments can change the color of food, and tea envy polyphenols have strong reducing properties and can prevent natural pigments such as carotene.

Chlorophyll, safflower yellow, carmine, etc.) fade by photooxidation, which has a certain effect on the stability of pigment.

4. Used as food deodorant.

Halitosis. It is mainly caused by volatile sulfur-containing compounds and nitrogen-containing compounds, among which hydrogen sulfide.

Sulfides such as methyl mercaptan have the strongest odor. Chewing gum containing tea polyphenols has 10 times more deodorizing power than ordinary chewing gum.

The role of tannins. Tea contains a lot of tannic spring acid, and the divalent iron is oxidized by the air into 3-valent iron, which forms black iron tannin with tannic acid. Ferric tannins are also the main ingredient of blue-black ink, and blue-black ink changes from blue to black in the air.

The tea leaves are alkaline, and the hydroxide meets the 2-valent history of iron infiltration to produce hydrogen and oxygen to starve and return iron, and the ferrous hydroxide meets oxygen to form iron hydroxide. Iron hydroxide itself is reddish-brown, but in large quantities, it is easy to see that it is black.

There is a weak acid in tea, tannic acid, which is oxidizing. The ferric ions, on the other hand, are reducible, so they react to form ferric tannins (black precipitate).

It's a very interesting chemistry. It turned out that one end of the glass rod was dipped in green alum (chemical name is ferrous sulfate) powder in advance, and the other end was dipped in oxalic acid crystal powder. Because the tea contains a large amount of tannins, when the tannic acid encounters the ferrous ions in the alum, it immediately generates ferrous tannin, its properties are unstable, and it is quickly oxidized to form a complex of iron tannin acid and is blue-black, so that the tea becomes "ink".

Oxalic acid is reducible, reducing trivalent iron ions to bivalent ferrous ions, so that the blue-black color of the solution disappears again, and the color of tea is reappeared. This phenomenon is also often encountered in people's lives, when you use a knife to cut the fruit that is not yet ripe, you often see the blue color of the fruit knife, some people think that the knife is not clean. In fact, this situation is the same as the above-mentioned tea to ink, which is the result of the chemical reaction between the iron on the knife and the tannic acid on the fruit.

The tea we often drink can be turned into black ink, and what is even more amazing is that "ink" can also be turned into tea, do you believe it?

We often drink tea in our daily life, there are Longjing, Tieguanyin, jasmine, etc., all kinds of tea colors, but none of the tea is black, but some magicians can turn two cups of mixed tea black.

It turned out that the magician had made his hands and feet in the water and put one of the cups in the alum. The tannic acid (tannic acid) contained in the tea can react with green alum to form a blue-black substance, iron tannin. It is used as a coagulant for the treatment of industrial clarification of turbid water, can treat wastewater containing chromium and cadmium, and is also used as a reducing agent and catalyst.

It can be used as a blood tonic and local astringent in medicine.

Another method is to apply some ferric chloride solution to the inside of the teacup lid beforehand, and the clean brush should be soaked with saturated oxalic acid solution. Place a little tea leaves in a transparent teacup and pour boiling water. Then cover and shake, and the tea will also turn into "ink".

When a brush soaked in oxalic acid was dipped in this cup of "ink" and ready to write, a miracle occurred, and the "ink" became "tea" again.

The reason is that tea contains tannic acid (tannin), which reacts with ferric chloride to form a black iron tannin precipitate, so the tea becomes "ink". Oxalic acid can react with ferric tannin to form colorless solubles, so "ink" becomes "tea" again.

Tea contains a large amount of tannic acid, which can turn water black when exposed to ferrous sulfate, and lemon extract can make water white.

Diacetic acid should be added to restore the original color of the tea, but it should not be drunk.

Because the tea contains a kind of tea polyphenols, well water contains iron, when the iron is oxidized to Fe3+, the tea polyphenols and Fe3+ have a chemical reaction and appear blue-purple, which not only increases the color of the purple buds and leaves, but also tastes more bitter.

It is oxidized to ferric iron.

Adding some iron powder or dripping some oil droplets in the water in advance can effectively prevent the oxidation of ferrous ions.

Prepare a glass bottle, put 3 grams of tannic acid in a cup, pour 3 liters of water, then put 4 grams of ferrous sulfate in the same way as tannins, pour in and stir until it turns black, then put 30 grams of oxalic acid in the same way as tannins, pour in and stir again, and it is done.

Alum bai is also known as: ferrous sulfate crystals. It can be used as a water purification agent

** Blood diseases and other DAOs.

Medicinal Value of Alum: Edition 1 Weak and swollen spleen. Use two catties to pan for power.

Atractylodes atractylodes soaked in rice water for two nights, four taels of yellow wine koji fried into red, add a pound of green alum, block vinegar, dry, calcine, grind finely, and then add vinegar and paste to make balls, which are used together with flat stomach and treat liver bloating.

2 The larynx is swollen and closed. Use green, mix in vinegar, dry, and blow the throat at the end of grinding. After the phlegm and saliva flow out, use a little minced ginger and rinse it in the tea to swallow.

3 The eyes are red and rotten. Use red dates to remove the core and add green alum, simmer, add two bowls of water and seven peach willow hearts, and fry them together. Apply to the eyes.

4 Malaria vomiting. Use green alum, soaked dried ginger, co-study for the end, and send down the vinegar soup.

5 Constipation. Use one penny of green alum, two pieces of bashuang, grind finely, put it in the egg and stir well, simmer it, and eat it with wine.

6 White bald sores. Use alum and neem seeds to refine and coat.

7 Rotten sores in the ears. Remove the core with dates, add green alum, grind finely after calcining, and adjust with sesame oil.

8 Burns. Rinse the alum powder with cool water and pour the wound.

Green alum is a chemical substance, is ferrous sulfate crystals, also known as ferrous sulfate heptahydrate, iron alum, its refined products are light blue green sandy crystals.

Answer: It is a columnar or granular aggregate with irregular blocks. Blue-green, green with streaks white. The molecular weight is 3, the pH value is 3, the melting point is 64 degrees Celsius, and the strong thermal decomposition is soluble in water, glycerol, and insoluble in ethanol.

It is widely distributed in arid areas, and is a weathering zone of iron-containing sulfide minerals (pyrite, pyrrhotite, etc.). In addition to the ancient production areas of Shanxi, Gansu, Anhui, Hubei and Sichuan, Shaanxi, Xinjiang, Shandong, Zhejiang, Henan, Hunan and other places have output.

Heptahydrate sulfate.

Bai iron is a columnar or granular DU aggregate, which is irregular in the form of zhi blocks. blue-green, DAO green; Streaks white.

Echo color. Transparent to slightly transparent. The surface is uneven, rough, and turns pale yellow after a long time in the air.

The texture is hard and brittle, and it can be scratched with a fingernail, easy to smash, and the mask is glassy. It is odorless, and the taste is first astringent and then sweet. It is better to have green, brittle quality and no impurities.

Feso4·7H2O, which can be used as traditional Chinese medicine, is mainly used to treat dampness and insecticide; replenish blood and eliminate accumulation; Detoxify sores. The main blood is deficient and chlorosorous; Accumulation of chancre; bloating and full; intestinal wind and blood in the stool; ulcering sores; laryngeal paralysis and aphthous ulcers; Rotten String Eye of the Wind; Scabies itching.