The concepts of acid and alkali in acid-base theoretical chemistry are constantly updated in the process of scientific development. Under the influence of ostwald at the end of 19, according to the theory of electrolyte dissociation, the concept of hydrogen ion is the embodiment of acidity, and the strength of acid is directly proportional to its concentration. Hydroxyl ion is the embodiment of alkalinity, and the strength of alkali is directly proportional to its concentration. Therefore, acid-base neutralization is a reaction in which hydrogen ions and hydroxyl ions interact to generate water. At that time, the concept was proved to be true by measuring the neutralization heat of different acids and bases. At the same time, it is found in experiments that the conductivity of pure water after impurity removal is very weak. So there are hydrogen ions and hydroxyl ions in the water, and people at that time have determined that the concentration product of ions in the water is 10- 14. At that time, it was generally believed that the dissociation of water might be expressed by the following equation: 2H2O=H3O++OH- its product is hydroxyl ion. At the same time, the conductivity of pure water was measured at 25℃, and the concentrations of H+ and OH- particles were both10-7mol/L. In 1909, Sorensen, a chemist in Copenhagen, proposed that the negative logarithmic PH of hydrogen ion concentration should be used to express hydrogen ion concentration. Although according to the principle of electrolyte dissociation theory, it seems that the concepts of acid and alkali are very clear, at the beginning of the 20th century, due to the discovery of many new experimental facts, the exact definitions of acid and alkali were put forward. Among many new discoveries at that time, the most representative fact is that when sodium acetate titrates hydrochloric acid by coulometry, the titration curve obtained is quite similar to that obtained when hydrochloric acid is titrated by alkali. As early as 1908, rapps, a scientist from Manchester, England, proposed that acid is the donor of hydrogen ions (that is, the donor of protons) and alkali is the acceptor of hydrogen ions based on the determination of the influence of water in alcohol solution. 1923, Lori, a professor at Cambridge University in England, Bronsted in Denmark, and Bjorum, both Danes, expanded these concepts simultaneously and independently. Among these three people, Bronsted has the most complete development of acid-base theory. According to Brinell's theory, acids should be various molecules or ions that can give protons (that is, protons to receptors). According to Bronsted, ammonium ion should be regarded as acid because it can give protons and generate NH3. . So ammonia is an alkali because it can accept protons. By extension, anions in acids can be regarded as bases. So the salt produced by acid should be alkaline. Bronsted's theory further demonstrates the necessary conditions for hydrogen radicals (or ions) to become proton donors. In 1923, Louis put forward a more general acid-base theory, which was further developed in 1928. Here, Louis took valence electron theory as the basis of his new theory. Accordingly, he thinks that alkali is any molecule containing lone electron pairs; An acid is a group or molecule that can bind to this lone electron pair. Lewis's acid-base theory holds that O, SO3, H+ and NH4+ are all acids. And CN- and OH- are both bases. Lewis's theory can explain many problems, such as why the color of indicator changes when titrating a solution containing no hydrogen ions. Following Lewis and others, the Soviet chemist Usanovic put forward a new viewpoint on acid-base reaction in 1939. Most substances without protons can be regarded as acids or bases. In fact, Usanovic's theory is greatly expanded on the basis of Bronsted's theory, and the result is all-encompassing. He thinks that cation or anion or electron acceptor is acid; Any substance that can accept any cation or anion and electron is a base. In this way, he regarded the salt-forming reaction, even the redox reaction, as an acid-base reaction process. So the concept of acid-base itself is becoming more and more vague. Bronsted, Lewis and Usanovic have their own advantages and disadvantages, and the concepts and theories of acid and alkali need to be further improved. Several acid-base problems in life Eating alkaline food can prevent cardiovascular sclerosis. Studies have found that eating more alkaline foods can keep blood weakly alkaline, reduce acid substances such as lactic acid and urea in blood, and prevent them from depositing on blood vessel walls, thus softening blood vessels. Therefore, some people call alkaline food "a cleaner for blood and blood vessels". The pH mentioned here is not the nature of the food itself, but the nature of the elements left in the body after digestion and absorption. Common acidic elements are nitrogen, carbon and sulfur. Common alkaline elements are potassium, sodium, calcium, magnesium and so on. Some foods, such as tomatoes and oranges, taste very sour, but they are all strongly alkaline foods because the last element after their metabolism in the body is potassium. Generally speaking, rice, noodles, meat, fish and eggs are almost all acidic foods, while vegetables, fruits, milk, sweet potatoes, potatoes, bean products and aquatic products are all alkaline foods. Pay attention to scientific diet, improve diet structure, strengthen physical exercise and form good habits. Angiosclerosis is expected to be delayed and reversed. In recent years, medical research has found that the pH of human body fluids is closely related to IQ. Within the allowable range of body fluid pH, people with high acidity have lower IQ, while people with high alkalinity have higher IQ. Scientists tested dozens of boys aged 6 to 13. The results show that the IQ of children whose body fluid PH is greater than 7.0 is higher than that of children whose body fluid pH is less than 7.0 1 times. It is known that the body fluids (mainly blood) of healthy people should be slightly alkaline (PH value is about 7.3 to 7.5), which is beneficial to the absorption and utilization of nutrients such as protein, keeping the blood circulation and immune system in a good state and making people more energetic. However, some children are grumpy, hyperactive, inattentive when studying, often feel tired and weak, and are prone to colds, dental caries, periodontitis and other diseases, which may be related to the high pH value of body fluids. The pH value of human body is mainly determined by the levels of acidic inorganic salts and alkaline inorganic salts in the body, which plays a decisive role not only in the self-regulation function in the body, but also in the food ingredients in the daily diet. According to the number of elements contained in food itself, it can be divided into alkaline food, acidic food and neutral food. Foods containing more elements such as potassium, calcium, magnesium and sodium, such as vegetables, fruits, milk, soybeans and fungus foods, are generally alkaline; Foods containing more phosphorus, chlorine, sulfur and other elements, such as meat, eggs, fish and other animal foods and flour, rice, peanuts, etc., are generally acidic; Some refined oil, sugar and starch are classified as neutral foods. In real life, children eat acid and alkaline food is not very balanced. Some children with poor academic performance and low intellectual development level are often acidic, so parents should pay attention to let them eat more alkaline food, which is very helpful to improve their IQ and academic performance. However, it must be pointed out that the child's body is still in the growth and development period, and it is in great need of all kinds of protein, fat, vitamins and minerals, and a considerable part of these essential nutrients exist in animal foods. Therefore, parents should reasonably arrange their children's three meals a day, try to match meat and vegetables, match the thickness, and eat acid and alkaline foods in a balanced way. If there is a deviation between the two, it is not good for the healthy growth of children. Are you drinking alkaline water? "Water is water, as long as it can quench your thirst, it is useless ..." Ten years ago, even five years ago, some people might say this. Now, the importance of drinking water to human body has been recognized by more and more people in China. However, in the current disturbing drinking water market with endless brands, how to choose a safe and healthy drinking water has become a real urgent matter. Do you know the nature of water? With the improvement of modern people's requirements for quality of life, more and more people have joined the fixed consumption groups of packaged drinking water. Indeed, bottled water and bottled water in the market, large and small, often give people a sense of trust: people put so much effort into bottles and sell water hundreds of times more expensive than tap water, which should always be a good thing. Besides, the water looks crystal clear without any impurities. You may be a little proud to say: all I drink at home is packaged water. But if you are asked to drink acidic water or alkaline water, do you know the answer? In fact, what you take for granted in life may be what you know the least. Two bottles of water that look exactly the same may be thousands of miles apart. Before choosing to buy packaged drinking water, it is best to know the nature of water: anyone with a little knowledge of chemistry knows the concept of PH value. PH value is commonly known as PH value. From 1 to 14, it is divided into 14, 1-7 is acidic, 7- 14 is alkaline and 7 is neutral. A fundamental factor that determines the "nature" of water is its PH value. According to the PH value, drinking water on the market can be divided into weakly acidic water and weakly alkaline water. The PH value of the former is generally between 5.0 and 7.0, while the latter is generally between 7.0 and 8.0. Fatigue may be related to drinking water. In the long-term life evolution, the human body has formed a relatively stable and slightly alkaline internal environment. Under normal conditions, the PH value of human body fluids is 7.04, that is to say, when the human body is in a slightly alkaline state, it is the most balanced and healthy. However, due to the large intake of high-protein and high-fat acidic foods by modern people, it is easy to cause acidification of human body constitution, resulting in weakened body function, slow metabolism, difficult discharge of various metabolic wastes and increased burden on internal organs. The most common manifestations are fatigue, constipation, colds, and serious chronic diseases such as high blood pressure. On the contrary, when the human body is in a normal slightly alkaline state, the metabolism is more active, the waste in the body is easy to be discharged, the body's immunity is stronger, and it is not easy to get sick. To maintain the acid-base balance in the body, food and drinking water are the most critical. Usually eat more alkaline foods rich in minerals and vitamins, such as milk, oranges, bananas, potatoes, cucumbers, mushrooms, kelp, onions and radishes. It is not advisable to eat too much meat because it is acidic. Similarly, when choosing daily drinking water, we should also choose weakly alkaline water. For water, whether it contains minerals and trace elements is the key to determine its acidity and alkalinity. Water in nature, such as spring water and lake water, is generally weakly alkaline water, because nature endows it with rich minerals and trace elements. Pure water, as its name implies, contains nothing but water molecules, and its aqueous nature is acidic. Reasonable collocation of acidic and alkaline foods Recently, people have been mentioning acidic and alkaline foods, so how can a reasonable collocation be regarded as alkaline food? This should be discussed from the environment in the human body. The internal environment of human body is basically neutral and slightly alkaline. A large number of acidic substances produced in the process of metabolism are neutralized by buffering substances in the blood, which will not make the internal environment of the human body acidic, but sometimes it will cause disorder. For example, when people have diarrhea, it is alkaline, and the acid in the body will increase relatively and become acidic; When vomiting a lot, the stomach acid loses too much, and the body can be alkaline. Moreover, every meal, food has a certain pH value, which will also affect the acid-base balance of the human body. The so-called acidity and alkalinity of food refers to whether the inorganic salts in food are acidic or alkaline. General metal elements such as sodium, calcium, magnesium, etc. They are all alkaline in the human body, and foods containing more of these elements are alkaline foods, such as soybeans, tofu, spinach, lettuce, radish, potatoes, lotus roots, onions, kelp, watermelons, bananas, pears, apples and milk. Some foods contain more nonmetallic elements, such as phosphorus, sulfur and chlorine. After oxidation in human body, acidic free radicals with anions are generated, which belongs to acidic food. Such as pork, beef, chicken, duck, eggs, carp, oysters and shrimp, as well as flour, rice, peanuts, barley and beer. Therefore, home cooking must pay attention to the reasonable collocation of acid-base food, otherwise eating too much acidic food will cause blood acidity. In order to neutralize these acidic substances, it will inevitably consume a lot of basic elements such as calcium and magnesium in the body, thus causing a series of symptoms such as calcium deficiency, such as skin diseases and neuropathy. Especially on holidays, if there is a lot of meat, we should pay more attention to matching some fresh vegetables, fruits and other alkaline foods, so as not to cause acid-base imbalance in the body. The knowledge of putting monosodium glutamate is sauerkraut. Never put monosodium glutamate, such as sweet and sour fish and sweet and sour ribs. Because monosodium glutamate is alkaline, if alkaline monosodium glutamate is added to acidic dishes, it will be chemically neutralized, that is, salt and water will be generated, and good dishes will have no taste. So can it be added to alkaline food? Practice has proved that monosodium glutamate in alkaline food will also lose its flavor. Therefore, monosodium glutamate should be placed in foods that are not obviously acidic or alkaline. Pay attention to the salinity of the dish when putting monosodium glutamate. If it is too salty, the sodium ions in the salt cover up the sodium, so you can't taste it; If it is too weak, the taste of monosodium glutamate will not "hang". Finally, pay attention to the temperature. The solubility of monosodium glutamate is 85 degrees Celsius. Below this temperature, the structure of monosodium glutamate has not been decomposed. Above this temperature, it is not appropriate to put monosodium glutamate, otherwise there will be no umami flavor. Avoid lining ancient books with foreign paper. Many rubbings, copybooks and paper-ink rubbings of the Republic of China are excellent, but the yellow spots on the layout are more embarrassing. This is because some calligraphers' workshops in the Republic of China, eager to save material costs, adopted a kind of paper called "glossy paper" (a cheap western-style industrial paper popular at that time) as the base paper of copybooks. Due to the improper pH of western-style paper, it has a certain corrosive force, which leads to many old posts in the Republic of China suffering from "yellow spots". This regret has also taught today's ancient book collectors a lesson, that is, China's ancient books must stay away from all western-style papers, and the best policy is to isolate them. References:
Sweet and sour