The role of chemistry is 1. Ensure the survival of mankind and continuously improve the quality of human life. Such as: using chemistry to produce fertilizers and pesticides to increase grain output; Using the chemical synthesis of drugs to inhibit bacteria and viruses and protect human health; Using chemistry to develop new energy and new materials to improve human living conditions; Using chemistry to comprehensively utilize natural resources, protect the environment and make human life better. 2. Chemistry is a practical subject, which, together with mathematics and physics, has become the basis for the rapid development of natural science. The core knowledge of chemistry has been applied to all fields of natural science, and chemistry is an important pillar of the powerful force to create and transform nature. At present, chemists use the viewpoint of chemistry to observe and think about social problems, and use chemical knowledge to analyze and solve social problems, such as energy problems, food problems, environmental problems, health problems, resources and sustainable development. 3. The intersection and infiltration of chemistry and other disciplines have produced many marginal disciplines, such as biochemistry, geochemistry, cosmochemistry, marine chemistry, atmospheric chemistry and so on. It has promoted the rapid development of biology, electronics, aerospace, laser, geology, ocean and other technologies. Most importantly, this is also the role of all scientific disciplines. Cultivate the psychology of continuous progress, discovery, exploration and curiosity, stimulate people's desire to understand nature and enrich people's spiritual world. Nowadays, chemistry is increasingly permeating all aspects of life, especially important issues closely related to the development of human society. In a word, chemistry is closely related to human clothing, food, housing, transportation, energy, information, materials, national defense, environmental protection, medicine and health, and resource utilization. It is a practical subject urgently needed by society. How is the chemical bronzing turning black in life? How can I restore dark bronze? Bronze will rust if left in the air for a long time. Copper will be oxidized into black copper oxide in humid air, and the copper oxide on the surface of copper will continue to react with carbon dioxide in the air to generate a layer of green basic copper carbonate CuCO3 Cu(OH)2) 2. In addition, copper will react with hydrogen sulfide in the air to produce black copper sulfide. Scrubbing a dark bronzed surface with cotton dipped in concentrated ammonia water will immediately shine. Because the surface of bronzes is scrubbed with concentrated ammonia water, copper oxide, basic copper carbonate and copper sulfide will be transformed into soluble cuprammonia complexes and removed. Or scrub with acetic acid to convert the dirt on the surface into soluble copper acetate, but this effect is not as good as the former. After washing, wash the bronzes with clear water, and the bronzes will shine again. How is the silverware turning black? What should I do to restore dark silverware? The blackening principle of silverware is similar to that of bronzes, because silver reacts with hydrogen sulfide in the air to produce black silver sulfide (Ag2S). To brighten the silverware, it is necessary to wash off the oil stains on the surface with washing powder, put them together with aluminum sheets, put them in sodium carbonate solution, and cook them until the silverware returns to silvery white. After taking out the silverware and washing it with water, you can see that the silverware surface is as bright as new. The chemical equation of the reaction is as follows: 2Al+3Ag2S+6H2O = 6Ag+2Al (OH) 3+3H2S plastic and plexiglass adhesive plastic products often appear in daily life. What if the plastic product is damaged? There are two kinds of plastic products, one is PVC, which is hard and brittle, and the other is polyethylene, which is relatively soft. Plexiglass is polymerized from methyl methacrylate. The best solvent for PVC is tetrahydrofuran. The solvent of plexiglass can be chloroform, dichloroethane and acetone. When bonding, plastic or plexiglass can be directly bonded with these solvents, or a small amount of plastic or plexiglass can be dissolved in solvents to make an adhesive with better effect. When lime is applied to the wall, cold water becomes hot. After lime is coated on the wall, it is not easy to dry, but the lime wall becomes harder and whiter. Why? When slaking lime, quicklime meets aquatic slaked lime, which is an exothermic reaction, so cold water will become hot. It is difficult to dry walls with lime, because hydrated lime [calcium hydroxide] reacts with carbon dioxide in the air to produce calcium carbonate and water. There is little carbon dioxide in the air and the reaction is slow. In addition, the formation of water makes it more difficult for walls to dry. When painting walls, lime slurry is calcium hydroxide, which is soft, and calcium carbonate generated after reacting with carbon dioxide is hard and white, so when calcium hydroxide is completely changed into calcium carbonate, it is hard and white. Ink precipitation ink is a colloid. When the ink bottle cap is not covered, with the evaporation of water, the ink thickens and the pigment colloidal particles are easy to squeeze together. Because the water layer between them becomes thinner, colloidal particles will combine into large particles and precipitate (called colloidal aggregation). In addition, the mixed use of different brands of ink will also lead to ink precipitation. Because colloidal particles are charged in order to stabilize them, inks made by different methods may have the same or different charges. When the inks with different charges in the colloidal particles are mixed, the charges disappear due to neutralization, and the colloidal particles become unstable and precipitate. Knowing this, it is best to wash the pen with clean water when changing other brands of ink or even different batches of the same ink. In addition, supercooling and overheating will also destroy the colloidal solution in ink, leading to precipitation. Therefore, the ink should be placed by the window in winter, not at high temperature in normal times. Alum water purification Our ancestors used alum to purify water a long time ago. The water treated with alum can remove 70-90% of suspended solids and bacteria. There are many tiny colloidal particles in suspended solids in water, and clay particles can adsorb anions and be negatively charged. After adding alum to water, positive trivalent aluminum ions neutralize the negative charge of clay particles, which makes them unstable and precipitate, and the water becomes clear. The source of "scale" and the long-used kettle, there is a layer of gray-yellow sediment on the boiler wall. Where did it come from? As we know, there are many inorganic salts such as calcium bicarbonate, magnesium bicarbonate and a small amount of calcium magnesium salts such as calcium sulfate and calcium chloride dissolved in water. Bicarbonate is easily decomposed into carbon dioxide and carbonate when heated, and carbon dioxide escapes into the air, while calcium carbonate is insoluble in water and magnesium carbonate is slightly soluble in water, so it will precipitate out, and the kettle and boiler that have been used for a long time will have "scale". Scale has poor thermal conductivity. Boiling water with kettles and boilers containing "scale" will cause energy waste. For factory boilers, when the "scale" is thick, it will automatically peel off a part, and uneven heating of each part will also cause an explosion. To remove the "scale", you can brush it with very dilute hydrochloric acid and acetic acid, then immediately pour out the acid solution and rinse it with clear water. As we all know, pearl cream contains glycerin, and the function of glycerin is to absorb the moisture in the air and keep the skin moist. So can pure glycerin be directly applied to the skin to moisturize? No, because if pure glycerin is directly applied to the skin, it can not only absorb the moisture in the air, but also absorb the moisture in the skin tissue. Strong fruit will make the skin drier and even burn. So when you buy glycerin, you must first ask whether it is pure glycerin or water-based glycerin. If it is pure glycerin, be sure to add 20% water to moisturize the skin. The fruit blackened by iron knife will contain an organic compound tannic acid more or less. Tannic acid will react with iron or other heavy metals to produce black iron tannins or other water-insoluble tannins, so the place where the knife touches the fruit will turn black. A small amount of tannin is harmless to human body, so don't worry about it. But you can't wipe the knife with a handkerchief, because iron tannic acid is insoluble in water and the black in the handkerchief can't be washed away. If you want to remove the black stains on the handkerchief, you should first wipe it with diluted oxalic acid solution, and then rinse it with clear water to be clean. The knowledge of decocting medicine should use pottery or ceramic cans, not metal cans such as iron cans and aluminum cans. Why? First of all, the crock is slow in heat transfer, and the effective components can be boiled out before the liquid medicine is completely dried. In addition, it is also to prevent the ingredients in the medicine from reacting with the metal pot to produce toxins or reduce the efficacy, and it will also corrode the pot. There is also a knowledge of decocting medicine, that is, using clear water. Because if the water contains more salt and calcium-magnesium plasma, the salt in the water will react with the ingredients of traditional Chinese medicine to form water-insoluble salts, and the use of fresh water can reduce the losses caused by the two. The lard boiled in water is more fragrant and tender than the lard not boiled in water. This is because when lard is not boiled in water, the temperature rises rapidly, and the oil boils before lard is boiled. When cooking continues, lard will decompose and give off a pungent smell, which is the smell of lampblack. In addition, the outer shell of the fat hardens to prevent the lard inside from boiling. At high temperature, the aromatic substances with unique flavor of lard escape, and the flavor becomes worse after cooling. But before boiling lard, add some water, boil the water first, and keep the temperature of the pot around the boiling point, so there will be no such disadvantages. The secret soup of aspic will solidify into aspic overnight, and it will come out after being left for a long time or stirred with chopsticks. Cook it again, let it cool, and it will condense into aspic. Why? Fish soup and broth will coagulate because meat (especially skin) contains animal glue. As long as the solution contains 1-5% animal gum or 0.2% plant gum (such as Lysimachia christinae), it will become "frozen". This is because the glue molecules disperse at high temperature, and when the temperature is gradually cooled to room temperature, the glue molecules will connect with each other to form many irregular meshes. The frozen internal glue molecules are continuously condensed, and the meshes are more dense, so some water is squeezed out, which will destroy its mesh structure and produce water, but after boiling and cooling, it will freeze again. The older the wine, the better it smells. Why does an ordinary wine become a fine wine after being buried for several years? The main component of wine is ethanol. After liquor was buried underground for several years, ethanol reacted with acetic acid, and C2H5OH+CH3 COOH → CH3 CO2H5+H2O produced CH3 CO2H5 (ethyl acetate) with fruity flavor. Although the above reaction is reversible and the reaction speed is slow, the longer the time, the more ethyl acetate is produced, so the older the wine, the more fragrant it is. Label of Pencil The refill of a pencil is made of graphite and clay mixed in a certain proportion. "H" is the prefix of "Hard" in English, which stands for clay and is used to indicate the hardness of pencil lead. The larger the number before "h" (such as 6H), the harder the pencil lead, that is, the greater the proportion of clay mixed with graphite in the refill, the less obvious the written words, which is often used for copying. "B" is the prefix of "black" in English, which stands for graphite, and is used to express pencil lead's softness and the obvious degree of writing. With "6B" as the softest and blackest handwriting, it is often used in painting, while ordinary pencils are generally marked as "HB". The pencil label used to paint the answer sheet during the exam is generally "2B". (Now the darkest pencil used for drawing is 9B.) Good medicine tastes bitter. Many traditional Chinese medicines contain some bitter active ingredients, such as coptis chinensis containing coptisine and ephedra containing ephedrine, so there is a saying that "good medicine tastes bitter". I accidentally broke the thermometer, which is usually filled with mercury. If the thermometer breaks down carelessly, mercury will leak out, and the spilled mercury will be scattered on the ground and in the air, causing environmental pollution and endangering human health. Therefore, after the thermometer breaks down, the spilled mercury should be properly disposed of. First, the larger particles of mercury can be absorbed by a straw, and then some sulfur powder is sprinkled on the remaining fine particles of mercury. Mercury reacts with sulfur to produce less volatile mercury sulfide-2hg+s = hg2s, which reduces the harm. You can't take medicine with tea. Usually take medicine with warm water. Why can't we use tea? Tea contains tannic acid, which will react with various components in the medicine, thus reducing the efficacy and even failing. For example, iron taken by anemia patients will react with tannic acid to form iron tannic acid, which is difficult to be absorbed by the human body. Antibiotics should be taken after meals. Most antibiotics are amine compounds. After people take it on an empty stomach, drugs are easily decomposed by gastric acid in the stomach, which not only reduces the efficacy, but also stimulates the stomach wall. When taking medicine after meals, because gastric acid is diluted by food, the medicine will not be decomposed by gastric acid, so antibiotics are generally taken after meals. Gold powder and silver powder for decorative patterns are made of brass (copper-zinc alloy). Brass sheet and a small amount of lubricant are crushed and polished to make "gold powder", which is widely used in paint and ink. "Silver powder" is made of aluminum, which is cheap and has the same silver luster as silver. Aluminum powder is light in weight, stable in air and highly reflective. There are two ways to make aluminum powder: one is to mix pure aluminum flakes with a small amount of lubricant and crush them mechanically; The other is to melt pure aluminum into liquid and spray it into fine aluminum powder. Brown sugar will turn sour for a long time, and white sugar will turn yellow for a long time. After long-term storage, brown sugar will gradually absorb water vapor in the air, so that lactic acid bacteria in sugar will multiply in large numbers. With the increase of lactic acid bacteria, sucrose, the main component of brown sugar, will gradually be converted into glucose and lactose, and then lactic acid will be produced. After a long time, lactic acid will be more and more, and brown sugar will be sour. In order to increase the whiteness of white sugar in the production process, there is a sulfur bleaching process, that is, sulfur dioxide is introduced into the sugar paste to reduce and decolor the pigment in the sugar juice. Decolorization by this method is not stable enough. If white sugar is in contact with air for a long time, the decolorized pigment will be oxidized by oxygen in the air to reproduce the color, so the white sugar will turn yellow after being kept for a long time. Plastic barrels are not suitable for long-term storage of edible oil. The raw material of plastic is synthetic resin. Plasticizer and stabilizer are added in the production process. These additives are toxic and soluble in edible oil, which makes the edible oil discolored and deteriorated, which is not only unsuitable for eating, but also shortens the life of plastic products. Therefore, do not use plastic barrels to store cooking oil. Color-changing glasses The lenses of color-changing glasses are made of photochromic glass. In the manufacturing process, a small amount of photosensitive substances, such as silver chloride and silver bromide, were added. A very small amount of sensitizer, such as copper oxide, is added to make the glass more sensitive to light. In the glass of color-changing glasses, silver halide decomposes in the sun, producing many black silver particles, which are evenly dispersed in the lens, and the lens turns black. When we return to the weak light, under the catalysis of copper oxide, silver and halogen recombine to form silver halide, so the color becomes lighter again. The reason why tap water is not suitable to be directly put into goldfish pond is because tap water is generally disinfected by chlorine, and chlorine and other substances are not good for the growth of goldfish, so it is best to put tap water in a basin and dry it in the sun for a day or two before using it to raise fish. Some people use plant ash to clean some cupboard appliances. Reason: plant ash contains a small amount of potassium carbonate, so plant ash's aqueous solution is alkaline and has a certain decontamination effect. Soak some valuable medicinal materials in medicinal liquor for drinking. Reason: Wine can slowly dissolve some useful substances in medicinal materials. When people drink medicinal liquor, they can absorb the beneficial components in medicinal materials and play the role of medicine. However, it should be noted that some people are allergic to alcohol and should drink according to their abilities. Why do you advocate the use of unleaded gasoline now? In the past, in order to reduce the vibration caused by the violent combustion of gasoline, lead-containing substances were added to gasoline. However, lead is a heavy metal, which is toxic. After burning, it will be discharged together with tail gas, seriously polluting the environment. The newly-built house is not suitable for immediate occupancy. Reason: The slaked lime used to build a house reacts with carbon dioxide in the air during the curing process to generate water, so the newly built house is relatively humid, and it is best to stay for one or two months. In addition, the newly renovated room will emit some harmful gases because of various paints and chemical coatings, so it should be ventilated before moving in 15 -30 days. Another function of the rust remover Another function of the rust remover is to burn honeycomb coal in winter. Because coal is wet, black water will flow out of the chimney after ignition. This kind of water can't be washed off with washing powder and soap, but it can be washed off with a small amount of "rust remover" Liquor is always stained with oil stains after dinner, so it is difficult to clean it with a hot rag. If you pour a little white wine on the dining table and wipe it back and forth with a clean rag several times, the oil stain can be removed. Iron drums can't store acidic food. Iron drums are galvanized iron drums. Zinc is a white, soft and shiny metal, which is easily soluble in acidic solution. If acidic foods and drinks are prepared or stored in iron drums or other galvanized utensils, zinc will be dissolved in food in the form of toxic organic acid salts, which may cause poisoning after people eat it. Therefore, when using galvanized containers, do not use them to hold acidic dishes, soup, wine, juice, milk and other beverages. In addition to the newly infected juice, you can sprinkle some salt first, moisten it gently with water, and then soak it in soapy water for cleaning. For slight fruit stains, you can wash them with cold water. If you can't wash it clean once, wash it again until it is clean. If the pollution is serious, you can use dilute ammonia water (1 part ammonia water to 20 parts water) to neutralize the organic acids in the juice, and then wash it with soap. Woolen clothes can be washed with tartaric acid solution. Silk can be washed with citric acid or with soap and alcohol solution. Drop a few drops of vinegar on the juice stain, rub it with your hands a few times, and then wash it with water.