Take a small glass, put it into the washed broken egg shell, add some vinegar (mainly acetic acid), and immediately cover it with a glass sheet soaked in clarified lime water. Observe carefully what happened. According to the experimental phenomenon, there may be something in the eggshell.

Experiments show that: ① families can make clear limewater. The main component of some food desiccants is quicklime, such as "strong desiccants" in laver. Take a glass, add about half a glass of water, add a pack of "strong desiccant", stir with chopsticks and let stand. Pay attention to the exothermic phenomenon of quicklime reacting with water. (2) When there is no glass at home, you can use a small mirror instead. ③ Experiments can also be done to clarify the blowing in limewater.

2, homemade soda

Add 2 spoonfuls of sugar and appropriate amount of fruit juice to a 500 mL beverage bottle, add about 1.5 g baking soda (sodium bicarbonate), inject cold water, then add about 1.5 g citric acid, immediately tighten the bottle cap, shake well and put it in the refrigerator. After half an hour, you can drink cool and sweet soda.

3. Write a secret letter with onion juice

Experimental supplies: onions (two), writing brush, white paper, candles.

experimental procedure

Take two onions, cut off their leaves, make them white, squeeze out onion juice, and then dip the onion juice with a brush and write on a piece of white paper. After a while, the onion juice dried up and the handwriting on the white paper disappeared. If this piece of white paper is baked by candlelight, the brown words will appear immediately. Onion juice can make paper undergo chemical changes, forming a substance similar to a transparent film with a lower ignition point than paper. It will burn when baked on the fire, so it will show brown handwriting. Lemon juice, garlic juice, onion juice and vinegar all have this property, so they can also be used to write secret letters.

Answer time: 23: 32 on February 4, 2008.

Chemistry in the kitchen

As we all know, people absorb nutrients by digesting food. The digestion process of food is a series of complex chemical reactions, and the speed of chemical reactions is closely related to the surface area of reactants, humidity and catalyst during the reaction. Protein, fat and starch in food are insoluble in water, which brings difficulties to people's digestion and absorption. After food is cooked, it absorbs water, expands and splits when heated, and some of it becomes water-soluble substances, which are easily catalyzed by enzymes in the gastrointestinal tract and absorbed by the human body. For example, starch particles are insoluble in cold water, but they will be absorbed, swollen, broken and turned into paste in warm water, and then react with water to turn very large starch molecules into many small molecules-oligosaccharides and monosaccharides. Rice, noodles and other staple foods contain a lot of starch, which is easily absorbed by the digestive system of the human body after cooking.

Cooking is not only a science, but also an art. A pile of lettuce, after being boiled, fried, boiled and stuffy, has become a dish with all colors and flavors, which is inseparable from the chef's skills and contains a lot of chemical knowledge. For example, in cooking, the order of adding condiments is sequential, not based on the operator's interest, otherwise the color, aroma and taste will be affected. The order of adding condiments depends on the penetration strength. Strong permeability is strong after. When cooking, put sugar first, then add salt, vinegar, soy sauce and monosodium glutamate. If the order is reversed, put salt first, which will hinder the diffusion of sugar. Because salt has dehydration effect, it will promote protein solidification, make the surface of food hard and tough, and the sweetness of sugar is difficult to penetrate. There are also individual principles, that is, odorless spices (such as salt and sugar) can be heated for a long time when cooking, while scented spices can't, so as to avoid the fragrance escaping. The main component of monosodium glutamate is sodium glutamate, which can't stand the high temperature of cooking and can only be added at the end.

When cooking food, the time of adding seasoning is also related to the chemical changes in food. Protein in food itself has the nature of colloid, which will condense when it meets strong electrolytes such as sodium chloride. For example, soy milk with salt will condense into tofu brain. If salt is added too early when cooking beans and burning meat, there is salt in the noodle soup, so it is difficult for water to penetrate into beans or meat; On the other hand, salt can make protein in beans or meat coagulate and harden. These two aspects make it difficult to cook beans or meat, and of course it is not conducive to human digestion and absorption.

The cooking temperature of food, that is, temperature, has a great influence on food. Generally speaking, increasing the temperature can speed up the reaction. For example, the temperature of stewing food is about 100 degrees (boiling point of water), and the temperature of frying is about 200 to 300 degrees (boiling point of oil is higher than water). The frying temperature is slightly lower than that of frying, but much higher than that of stewing. Therefore, it takes several times more time to cook and simmer the meat than to fry it, and the temperature in the pot is also related to mixing and frying. Stir-frying can make food heated evenly, but excessive stir-frying will reduce the temperature in the pot, increase the chance of food contacting with oxygen in the air, and make vitamin C in food easy to be destroyed by oxidation. Therefore, the pot cover must be added after cooking. First, it can prevent the pot temperature from decreasing. Second, it can prevent vitamin oxidation and reduce nutritional value.

Many families like to add some wine when cooking fish. What do you think this is? There is more trimethylamine in dead fish, so the longer the fish dies, the stronger the smell. Trimethylamine is insoluble in water and soluble in alcohol, so adding wine when cooking fish can remove the fishy smell and make the fish taste better. Wine can remove the fishy smell of fish and meat; The role of wine is not limited to this. When cooking, the fat in food will be partially hydrolyzed to produce acid and alcohol. When wine (containing ethanol), vinegar (containing acetic acid) and other seasoning accessories are added, acid and alcohol undergo esterification reaction to form aromatic esters.

Chemistry is everywhere in the kitchen. For example, liquefied gas is a mixture of some lower hydrocarbons, and the small molecules of hydrocarbons-oligosaccharides and monosaccharides. Rice, noodles and other staple foods contain a lot of starch, which is easily absorbed by the digestive system of the human body after cooking.

Explore chemistry in the kitchen

The kitchen is a housewife's little world. Every family has a kitchen, but the chemical knowledge involved in the kitchen can be seen everywhere. For example, what if the oil pan catches fire? How to deal with gas leakage? How to treat domestic sewage?

Most of our kitchens have: wine, vinegar, running water, salt, eggs and so on.

The main component of vinegar is acetic acid (CH3COOH), and its chemical name is acetic acid. Acetic acid can only ionize hydrogen ions (H+) and acetate ions (CH3COOO—-) in water, and can also be replaced by active metals to reflect the generation of hydrogen, so household aluminum products should not be used for vinegar to avoid corrosion. Have you noticed? When cooking bone soup, parents will add a small amount of vinegar to the soup. Why? Because bone contains calcium phosphate, which is insoluble in water, calcium phosphate reacts with acetic acid to produce water-soluble calcium dihydrogen phosphate, which can increase the calcium content in soup and is beneficial to the growth of students.

In the kitchen, the daily necessary procedures include washing vegetables, so the daily water consumption is very large, and the daily sewage discharge is countless.

Count. However, many countries and regions are short of fresh water resources, and how to solve the water problem is the focus of discussion today. Since we can't dig out new sources of fresh water, can we start with saving water? How can we reuse domestic sewage? How to remove the residue and odor in broken vegetable leaves, sediment and sodium chloride?

To remove the broken vegetable leaves and sludge in sewage, relatively pure water can be obtained by filtration. Dissolution and filtration are carried out in two steps, and then the odor of sewage can be removed by adsorption of activated carbon. The water obtained after a round of treatment can be used as toilet cleaning water or watering flowers and grass. In this resource-poor environment, sewage reuse can reduce sewage discharge, reduce water pollution, save water resources and reduce the cost of domestic water. Turn waste into treasure. We can also do some interesting laboratory tests through kitchen supplies, such as making "eggshells". When an egg is placed in a glass tube filled with vinegar, it will sink to the bottom of the tube, and bubbles will be generated on its surface, which will rise slowly. Because the eggshell is CaCO3, CaCO3 +2HCl=CaCl2+CO2↑, the eggshell is born! Moreover, the application of eggs is not limited to these. We often use limewater to insure eggs, because limewater has bactericidal effect.

Life is like a kaleidoscope. The chemical reaction in the kitchen alone can dazzle you. Grasp your curiosity about the things around you and you will get unexpected gains.