After BC, China and Europe entered the period of alchemy and alchemy. China has been researching medicine for refining elixirs. The earliest pharmaceutical monograph completed in the Qin and Han dynasties, Shennong's Materia Medica, contains 365 kinds of animal, plant and mineral medicines. In the 16th century, Li Shizhen's "Compendium of Materia Medica" summarized the achievements of previous medicines, which had a high academic level. In addition, in the 7th~9th century, there were records of the mixing method of the three components, and gunpowder was used for military purposes in the early Song Dynasty. Europe has been superstitious about alchemy since the 3rd century, and it was not until the 15th century that alchemy gradually turned to medicine, and the history is called the 15th ~ 17th century as the pharmaceutical period. In pharmaceutical research, chemicals such as sulfuric acid, nitric acid, hydrochloric acid and organic acids are prepared in the laboratory for the preparation of drugs. Although it did not form an industry, it led to the development of chemical preparation methods, which prepared the conditions for the establishment of the chemical industry in the mid-18th century.

The early chemical industry was in its infancy from the mid-18th century to the early 20th century. At this stage, the inorganic chemical industry has begun to take shape, the organic chemical industry is taking shape, and the polymer chemical industry is in the embryonic stage.

The first typical chemical plant of inorganic chemical industry was the lead chamber sulfuric acid plant established in England in the 40s of the 18th century. First sulfur was used as raw material, and then pyrite was used as raw material, and the products were mainly used to make nitric acid, hydrochloric acid and drugs, and the output was not large at that time. During the Industrial Revolution, the textile industry developed rapidly. It and glass, soap and other industries use a large amount of alkali, while plant alkali and trona are in short supply. In 1791, under the reward of the French Academy of Sciences, N. Lüblin obtained a patent to build a factory with salt as raw material to produce soda ash, and promote the development of sulfuric acid (one of the raw materials) industry; Filling devices for absorbing hydrogen chloride, rotary furnaces for calcining raw materials and semi-finished products, and equipment for concentration, crystallization, filtration, etc., are gradually used in other chemical enterprises, laying the foundation for the operation of chemical units. The Lübran method was gradually replaced by the Solvay method (see soda ash) at the beginning of the 20th century. At the end of the 19th century, the chlor-alkali industry of electrolytic table salt appeared. In this way, the production of acids and alkalis, the basis of the entire chemical industry, has begun to take shape.

After the development of the organic chemical textile industry, natural dyes can not meet the needs; With the development of the steel industry and coking industry, the by-product coal tar needs to be utilized. Chemists have used the achievements of organic chemistry to separate coal tar into benzene, toluene, xylene, naphthalene, anthracene, phenanthrene and other aromatic hydrocarbons. In 1856, the Englishman W.H. Perkin synthesized aniline violet dye from aniline, and then determined that the structure of natural alizarin was dihydroxyanthraquinone, and then used anthracene in coal tar as raw material, and imitated the same product as natural alizarin after oxidation, substitution, hydrolysis, rearrangement and other reactions. Similarly, the pharmaceutical industry and the fragrance industry have also synthesized chemicals that are the same as natural products, and the varieties are increasing day by day. In 1867, the Swede A.B. Nobel invented the dynamet explosives (see Industrial Explosives), which were widely used in mining and military industry.

At that time, there was another pillar of organic chemical production, acetylene chemicals. In 1895, the first factory was established to produce calcium carbide (i.e., calcium carbide) by electrothermal method using coal and limestone as raw materials, and calcium carbide was then hydrolyzed to produce acetylene, which was used as a starting point to produce a series of basic organic raw materials such as acetaldehyde and acetic acid. After the development of petrochemical industry in the middle of the 20th century, the energy consumption of calcium carbide was too high, and most of the original acetylene series products were produced by ethylene as raw material.

Polymer material: Natural rubber sticks when heated, and hardens when cold. In 1839, C. Goodyear of the United States used sulfur and rubber additives to heat natural rubber to cross-link it into elastomer, which was widely used in tires and other rubber products, which was the embryonic period of polymer chemical industry. In 1869, J.W. Hayt of the United States used camphor plasticized nitrocellulose to make celluloid plastic, which is very valuable. In 1891, H.B. Chardonnet built the first nitrocellulose rayon factory in Besançon, France. In 1909, L.H. Beckland of the United States made phenolic resin, commonly known as bakelite powder, which was the first thermosetting resin, which was widely used in electrical insulation materials.

These budding products are far from meeting the requirements of society in terms of variety, output, and quality. Therefore, the production of the above-mentioned basic organic chemicals and the production of polymer materials have been greatly developed after the establishment of petrochemical industry.

Purification of substances

The purification of a substance refers to the process of removing other impurities from a substance to obtain a purer substance. When answering such questions, it is necessary to take into account the state of existence of the substance, the differences and connections in physical and chemical properties between the purified substance and the impurities, and then decide which reagent to use and which method to use. The common solutions to the problem of material purification are summarized as follows:

1. Take advantage of the differences in the physical properties of matter

Example 1: Remove a small amount of HCl gas mixed with Cl2.

Analysis: (Solubility Difference Method) The mixed gas is removed by passing it through saturated saline and dissolving HCl gas in saturated saline solution.

Example 2: Remove a small amount of NaCl impurities mixed with solid KNO3.

Analysis: (crystallization method) The mixture is first made into a saturated solution at high temperature, and then gradually cooled to make KNO3 crystals precipitate, and then filtered to obtain KNO3 crystals.

Example 3: Remove a small amount of bromine from hydrobromic acid.

Analysis: (Extraction and separating method) hydrobromic acid mixed with bromine is added to the separating funnel, and then the extractant CCl4 is added, and the lower liquid is separated after full shaking, and the obtained upper liquid is hydrobromic acid.

Example 4: Removal of sediment mixed with iodine.

Analysis: (sublimation method) heating sublimates iodine, and then collects iodine to remove sediment.

Example 5: Remove a small amount of salt impurities mixed in a liquid-sol.

Analysis: (dialysis method) put the colloid mixed with salt impurities into a semi-permeable membrane bag, tie the mouth of the bag, tie the bag to the glass rod, and then hang it in the flowing distilled water, after a period of time, the colloidal will be dissolved into the water through the semi-permeable membrane, so that the colloid can be purified.

Example 6: How to obtain the pure substance of A and B when the boiling point of A and B is known to be 35 °C and the boiling point of B is 200 °C?

Analysis: (distillation method) The mixture of A and B is distilled, and then the fraction at 35 °C is collected to obtain substance A, and substance B is left in the flask.

2. Take advantage of the differences in the chemical properties of substances

The key to chemical purification is the correct selection of chemical reagents, and attention should be paid to when selecting reagents:

(1) The selected reagents can generally only react with impurities;

(2) Impurities cannot be introduced in the process of purifying substances;

(3) The products generated by the reaction between impurities and reagents should be easily separated from the purified substances;

(4) The purification process should be simple, the phenomenon should be obvious, easy to separate, and the purity of the obtained product should be high;

(5) Convert impurities into the desired substances as much as possible.

The commonly used methods are: thermal decomposition method, redox method, precipitation method, etc.

Example 7.Remove a small amount of NaHCO3 mixed in the Na2CO3 solid.

Analysis: (Thermal decomposition method) The mixture of the two is heated to make the decomposition become.

Example 8: Remove a small amount of toluene mixed with benzene.

Analysis: (redox method) add acidic potassium permanganate solution to the mixture to oxidize toluene to benzoic acid, and then neutralize it with NaOH solution to convert it into sodium benzoate into water and stratify with benzene, and then separate it with a separating funnel to remove it.

Example 9: Removal of H2S gas mixed with CO2 gas.

Analysis: (precipitation method) the mixed gas can be removed by passing the mixed gas through a washing cylinder containing CuSO4 solution.

Example 10: Remove a small amount of mixture.

Analysis: (dissolution method) using the amphoterides, adding excess NaOH solution to the mixture, filtering after complete reaction, can remove impurities.

Example 11: Remove a small amount of SO2 gas mixed with the gas.

Analysis: (washing method) The mixed gas is passed through the NaOH solution, and the SO2 gas can be removed:

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The English word for chemistry is Chemistry, the French word Chimie, and the German word Chemie, which are all derived from an ancient word, namely the Latin word chemia, the Greek word Xηwa (Chamia), the Hebrew word Chaman or Haman, the Arabic word Chema or Kema, and the Egyptian word Chemi. Its earliest sources are difficult to trace. According to the extant sources, it first appeared in the records of Egypt in the fourth century. Therefore, some people think that it can be assumed to come from the ancient Egyptian word Chemi, but the meaning of the name is very obscure, and it has the meaning of Egypt, Egyptian art, religion, bewilderment, concealment, secret, or darkness. This is probably because Egypt is the place where chemical records were born in the West, and it is also a place where ancient chemistry was extremely developed, especially in practical chemistry. For example, Egypt already had an engraving in the Eleventh Dynasty showing some workers making glass, suggesting that Egypt knew how to make glass at least until 2500 B.C. From the mummies unearthed in Egypt, it can be seen that in the first and second millennium BC, they were proficient in the use of preservatives and cloth dyeing techniques. So the ancients named "chemistry" after Egypt or Egyptian art. As for the other meanings, it may be because the ancients believed that chemistry was a miraculous and secret enterprise, as well as religious overtones. Topic: The historical origin of chemistry is very ancient, and it can be said that the earliest chemical practice began when humans learned to use fire. Our ancestors drilled wood to make fire, used fire to bake food, kept warm on cold nights, drove away wild beasts, and made full use of the glow and heat phenomenon when burning. At the time, it was just an accumulation of experience. The formation of chemical knowledge and the development of chemistry have gone through a long and tortuous road. It develops along with the progress of human society and is the inevitable result of social development. And its development promotes the development of productive forces and the progress of history. The development of chemistry mainly goes through the following periods: (1) The embryonic period of chemistry: from ancient times to 1500 B.C., human beings learned to make pottery from clay in the blazing fire, burned metals from ores, learned to brew wine from grains, and dyed silk and linen and other fabrics. (2) The period of alchemy and medicinal chemistry: From about 1500 BC to 1650 AD, chemistry was controlled by alchemy and alchemy. In order to obtain the elixir of immortality or gold, a symbol of wealth, alchemists and alchemists began the first chemical experiments, and then books recording and summarizing alchemy also appeared. Although the alchemists and alchemists all ended in failure, in the process of refining the elixir of life, they realized the mutual transformation of substances by artificial methods in exploring the method of "turning stones into gold", accumulated many conditions and phenomena for chemical changes in substances, and accumulated rich practical experience for the development of chemistry. At that time, the word "chemistry" came up and its meaning was "alchemy". However, with the decline of alchemy and alchemy, people saw more of its absurd side, and chemical methods were turned to medicine and metallurgy, and the development of Chinese and foreign pharmacology and metallurgy prepared rich materials for chemistry to become a science. (3) Phlogiston chemistry period: This period from 1650 to 1775 is the gestation period of modern chemistry. With the accumulation of metallurgical industry and laboratory experience, people summarize perceptual knowledge and carry out theoretical research on chemical changes, making chemistry a branch of natural science. The beginning of this phase was marked by the British chemist Boyle pointing out the scientific concepts of chemical elements. Subsequently, chemistry was liberated from alchemy through phlogiston. Although the phlogiston theory holds that combustibles can be burned because it contains phlogiston, and the combustion process is the process by which phlogiston is released from combustibles, although this theory is wrong, it unifies a large number of chemical facts under one concept and explains many chemical phenomena. In the more than 100 years since phlogiston theory became popular, chemists have done a lot of experiments to explain various phenomena, discovered the existence of a variety of gases, and accumulated more new knowledge about the transformation of matter. In particular, the phlogiston theory, which believes that a chemical reaction is a process by which a substance is transferred to another and that a substance is conserved in a chemical reaction, laid the foundation for modern chemical thinking. During this period, not only from the scientific practice, but also from the ideological point of view, the development of modern chemistry was prepared, and this period became the gestation period of modern chemistry. (4) Quantitative Chemistry Period: This period from 1775 to 1900 was the period of modern chemistry development. Around 1775, Lavoisier expounded the oxidation theory of combustion with quantitative chemical experiments, which ushered in the period of quantitative chemistry and brought chemistry on the right track. At the beginning of the 19th century, the British chemist Dalton proposed the modern atomic theory, and then the Italian scientist Avogadro proposed the concept of molecules. It was only since the atomic-molecular theory was used to study chemistry that chemistry was truly established as a science. During this period, many fundamental laws of chemistry were established. The discovery of the periodic law by the Russian chemist Mendeleev and the development of the organic structure theory by the German chemists Liebig and Weiler all made chemistry a systematic science and laid the foundation for the development of modern chemistry.