Chemistry in life

Chemistry is closely related to people's lives, and a lot of chemical knowledge can be accumulated from daily life. In this way, we can deepen our understanding of what we have learned and thus improve our interest in learning chemistry.

Salt is salty and is often used for seasoning or pickling fish, eggs and vegetables. It is the most widely used condiment and is known as the "king of all flavors". People should eat a certain amount of salt every day (6 grams to 15 grams of salt is enough for adults every day). One reason is to increase the taste, and the other is the need of human function. Na+ mainly exists in extracellular fluid and is an important component to maintain osmotic pressure and volume of extracellular fluid. The salt concentration in animal blood is constant. Excessive loss or insufficient supply of salt will increase excitability, which will lead to weakness and trembling, and finally lead to paralysis of animals' hind legs until death. American scientist Taylor personally experienced the process of eating salt-free food. At first, sweating increased and appetite disappeared. Five days later, he felt very tired. On day 8-9, he felt muscle pain and stiffness, and then he suffered from insomnia and muscle twitching. Later, because the situation was more serious, he was forced to terminate the experiment. Of course, eating too much salt will absorb the water in cells back into body fluids, making the body have a fever due to lack of water.

The process of transforming nitrogen in the air into nitrogen-containing compounds that can be absorbed by plants is called nitrogen fixation. There are usually two kinds of nitrogen fixation in nature: one is that nitrogen oxides in the air produce nitric oxide when lightning strikes, and nitric oxide further combines with oxygen to produce nitrogen dioxide, which is absorbed by water to become nitric acid and falls to the ground when it rains. Another way to fix nitrogen is to use rhizobia of plants. Rhizobia is a kind of bacteria that can form nodules in the roots of leguminous plants. Under natural conditions, it can transform nitrogen in the air into nitrogen-containing compounds for plants to use. This is the truth that "growing beans is not fat, but growing them for a few years is fatter".

Preserved eggs are the traditional food of our people. Because of its unique flavor, excellent taste and long shelf life, it is deeply loved by people. Do the students know? In fact, the process of processing fresh eggs into preserved eggs is a complex chemical process. Strong alkali (sodium hydroxide and potassium hydroxide) in the ash material permeates into the egg yolk and egg white from outside the eggshell, and reacts with protein in the egg yolk and egg white, so that protein decomposes, solidifies and releases a small amount of hydrogen sulfide gas. At the same time, the infiltrated alkali further reacts with the amino acids decomposed by protein, and the crystals of the generated salt condense into beautiful shapes in the egg white, like blossoming "pine flowers". Hydrogen sulfide gas reacts with minerals in egg yolk and egg white to generate various sulfides, so the colors of egg yolk and egg white change. Egg yolk is dark green and egg white is special tea green. Salt can shrink preserved eggs from eggshells, increase flavor and prevent corrosion. The added lead can accelerate the ripening of preserved eggs and promote the shrinkage and shelling of preserved eggs. Tannin and aromatic oil in tea can solidify and color protein, and increase the flavor of preserved eggs.

Attachment: Key points of chemical knowledge in life

First of all, about the burning of matter.

1. Light two candles with different heights and cover them with a beaker. The tall candle goes out first, because the generated carbon dioxide gas has a high temperature, rises and then fills the whole bottle from top to bottom. Therefore, when there is an indoor fire, cover your nose and mouth with a wet towel and bend down to escape from the fire. The way to escape from forest fire is to block your nose and mouth with a wet towel and escape against the wind.

In order to ensure safety, helium can be used to inflate the balloon during the celebration, but hydrogen can't be used.

Gas poisoning is caused by carbon monoxide. The effective way to prevent gas poisoning is to pay attention to ventilation. In order to prevent gas leakage, we often add mercaptan (C2H5SH) with special smell to the gas to understand the gas leakage. When gas leakage is found, open the doors and windows in time and close the gas valve. No lights, no phone calls, no electric fans, etc. Because of these behaviors, there will be sparks and gas explosions. When someone is found to be poisoned by gas, attention should be paid to moving the patient to a ventilated place for manual labor.

4. The candle goes out as soon as it is blown, because the cold air lowers the temperature of the candle below the ignition point, while the fan fire is more and more popular because it provides enough oxygen and increases the contact area between coal and oxygen.

5. The gas for the west-to-east gas transmission is natural gas, and its main component is methane. The main gas of coal mine gas explosion is methane. The reason is the poor ventilation in the mine, which makes the mixture of methane and air reach the explosion limit and explode after being ignited. Therefore, in order to prevent coal mine explosion, it is necessary to keep ventilation and prohibit fireworks.

6. There is often a small amount of red phosphorus in the light bulb, mainly to remove the oxygen in the lamp.

7. In case of fire, block your nose and mouth with a wet towel to prevent inhalation of toxic gas. In case toxic gases (including chlorine, hydrochloric acid, hydrogen sulfide and ammonia) leak, cover your nose and mouth with a wet towel, and then flee to higher ground.

Second, about food.

1. Fresh eggs can be kept fresh in limewater, because the carbon dioxide exhaled by eggs reacts with limewater to generate calcium carbonate, which blocks the micropores on the surface of eggs and prevents oxidative deterioration.

2. In order to prevent food from getting wet, deteriorating or deforming, food bags are often filled with carbon dioxide or nitrogen; Or put desiccant in the bag: quicklime and calcium chloride mainly absorb water, and iron mainly absorbs oxygen and water; Or vacuum package.

3. The main gases in swim bladder are carbon dioxide and oxygen.

4. Adding some soda ash when making steamed bread is mainly to neutralize the acid generated during flour fermentation, and the generated carbon dioxide can make bread loose and porous.

5. The residual pesticides in vegetables can be soaked in alkaline substances, which can reduce the medicinal properties of pesticides.

6. Adding vinegar can remove the astringency of preserved eggs.

7. The odor of refrigerator can be removed by activated carbon, that is, the adsorption of activated carbon is utilized.

8. The scale on aluminum pot (mainly composed of calcium carbonate and magnesium hydroxide) can be removed by hydrochloric acid or vinegar.

Third, environmental issues.

1. Acid rain is caused by a large number of nitrogen oxides and sulfur oxides (such as SO2 and NO2). The hazards of acid rain include: corroding buildings, affecting crop growth, polluting rivers, affecting human health and land acidification. Measures to reduce acid rain: open up new energy sources, use less coal as fuel, and develop coal-fired desulfurization technology.

2. Automobile exhaust contains carbon monoxide, nitric oxide, sulfur dioxide, etc. The treatment methods are: changing the engine structure to make the fuel burn fully; A catalytic converter is installed on the exhaust pipe to convert CO and NO into nontoxic N2 and CO2. The methods to control the air pollution caused by automobile exhaust in cities are: (1) developing new energy sources, (2) using electric vehicles.

3. Methods to prevent water pollution:

Strengthen the monitoring of water quality

(2) The industrial three wastes should be treated and discharged.

(3) rational use of pesticides and fertilizers

(4) It is forbidden to use phosphorus-containing washing powder.

(5) Strengthen soil and water conservation and plant trees.

Water-saving methods: the secondary utilization of water (washing rice and watering flowers), turning off the tap at will, low irrigation technology, and the secondary utilization of industrial water.

4. Greenhouse effect

Due to the use of coal and petroleum fuels, the content of carbon dioxide in the air is increasing. The adverse effects are: global warming, land desertification and melting of polar glaciers; The measures that can be taken are: planting trees and prohibiting deforestation; Reduce the burning of fossil fuels and make more use of solar energy, wind energy, geothermal energy, nuclear energy and hydropower (we can save paper, save energy, plant more trees and turn off the lights at will)

(B) How to learn chemistry well

Middle school chemistry is very basic, and the reactions between substances should be clarified. There are not many chemical equations involved in junior high school, but they are all very important and should be kept in mind. There is also more practice. Without practice, it is difficult to learn science courses well. Practice makes perfect. If you do more, you will feel better. In fact, self-confidence is still very important. You can believe what others can do well!

The clear purpose of learning chemistry

Goals are the driving force of action. With a clear learning goal, it is possible for you to overcome all difficulties, go forward bravely, and finally reach the set learning goal. Therefore, to learn chemistry well, the first task is to make clear why you want to learn chemistry.

Chemistry is a natural science and a compulsory course in middle school. Including some basic chemical concepts, basic theories, knowledge of elemental compounds, basic types of chemical reactions, classification of inorganic substances and their relationships. It is full of the principles and contents of materialist dialectics, and introduces the excellent qualities of many scientists, the scientific attitude of seeking truth from facts and the rigorous style of study.

By studying chemistry and understanding the principle of chemical change, we can understand some phenomena in life and production, control chemical change and make it develop in a direction beneficial to human beings; Learning chemistry can not only extract substances that originally existed in nature, but also make substances that originally did not exist in nature, enriching and optimizing our production and life; Learning chemistry can help people develop new materials, study new energy sources, study life phenomena, make rational use of resources, prevent pollution and protect the environment, promote agricultural production and promote human health. Studying chemistry can also help people to study and further study natural sciences such as physics, biology and earth science.

Therefore, through the study of junior high school chemistry class, junior high school students can not only learn the systematic basic knowledge of junior high school chemistry, but also be educated by dialectical materialism, patriotic thoughts and behaviors of Chinese and foreign chemists, scientific attitude of continuous exploration and innovation, and rigorous study style. They can also improve their observation ability, thinking ability, experimental ability and self-study ability, and lay a good foundation for studying senior high school chemistry and other technologies in the future.

Second, grasp the three links of learning.

Chemistry is an additional course after grade three, with independent content and not influenced by other disciplines. There is no difference for every student who has just entered the third grade. As long as we can grasp the three learning links of preview, listening and review, we will certainly achieve excellent academic results.

1. Preview before class

Preview before class has many advantages: (1) it can strengthen the pertinence of listening, help to find problems, grasp key points and difficulties, and improve listening efficiency; (2) It can improve the level of taking class notes, knowing what to remember, what not to remember, what to remember in detail and what to remember slightly; (3) It can save time for reviewing and doing homework after class. Shorten the time of reviewing and doing homework after class through independent thinking in preview and deep impression left in class; (4) Self-study ability can be cultivated. The process of preview is a process of conscious or independent thinking. If you persist for a long time, your self-study ability will improve.

The method of preview is: (1) Read through the text. By reading the text, you can understand the basic content and key points of the new lesson. You should write down the questions you don't understand or make some marks on the book with a pencil to remind yourself to pay attention in class, listen to the teacher's questions you don't understand consciously and purposefully, and compare them with your own ideas in detail, so as to achieve good learning results. (2) Remove obstacles. On the basis of reading the text and understanding the main content, contact the basic knowledge related to it that has been learned. If there is any forgotten place, review it in time to make up for it, so as to connect the old and new knowledge and bring the new with the old to review the old and learn the new; (3) Determine the key points, difficulties and doubts. After reading through the text and clearing the relevant obstacles, on the basis of understanding the new knowledge, think about the exercises after the text, try to answer them, and find out the key points, difficulties and doubts of the new lesson in the process. If you have the potential, you can also take some preview notes.

Step 2 listen in class

Listening to lectures is the core link in the learning process and the main way to learn and master knowledge. Whether you can master what you have learned in class is the key to determine the learning effect. The merit lies in the classroom and the benefit lies in the classroom. If you can basically master the basic knowledge and skills learned in class, there will be no difficulty in reviewing and doing homework after class. If you don't pay attention in class and don't understand in class, problems that can be solved in a few minutes may take several times to make up after class. Therefore, it is the key to let students concentrate on listening to each lesson in class.

When listening to the class, you must concentrate on it, not only listen carefully to the teacher's explanation, but also pay special attention to the ideas that the teacher has said and the key points and difficulties that have been repeatedly emphasized. While listening to the class, take notes, mark or write down what you don't understand, and ask the teacher or classmates in time after class. At the same time, in class, we should also pay attention to students' answers to teachers' questions and teachers' evaluation of students' answers: which are correct and which are incomplete, inaccurate and wrong, so as to deepen our understanding of knowledge and judge right and wrong. Classroom teaching is a two-way activity of teaching and learning. Students are the main body and teachers play a leading role. Students should actively participate in classroom teaching. In class, we must eliminate all distractions and distractions, keep our eyes on the teacher, follow the teacher's lectures and demonstrations, think positively, observe carefully, speak enthusiastically, remember in time, seize the time given by the teacher in class, do a good job in class exercises and try to digest what we have learned in class.

While listening carefully, you should also take notes carefully. Taking notes is also an important part of learning chemistry well. Taking notes can not only concentrate and improve the efficiency of class, but also help you review after class. So learn to take notes and form a good habit of taking notes. Therefore, while listening carefully, we should also take notes. Make supplementary notes in the new class. The content of the teacher's lecture is to reorganize the content of the textbook according to the students' reality and highlight the key points. Taking notes means reading and listening, marking the book, marking the key points that the teacher said, and copying the outline and key points that the teacher wrote on the blackboard while talking. It is also necessary to briefly record the key, regular, substantive content and inspiring places, and write down the examples that the teacher said but not in the book.

The current textbook of People's Education Edition has a blank space beside each page, which is designed for students to take notes while learning. Students can write notes next to the corresponding content of the text according to the content to be recorded, which is helpful to contact knowledge and enhance understanding and memory in future review.

3. Review in time after class

Review can deepen understanding and consolidate knowledge. The content of a class can be reviewed in more than ten minutes, and sometimes it can be repeated like a movie.

The review should be timely, not delayed. Ask the teacher if you don't understand the questions in the review, so as not to leave obstacles and doubts in the study and lay a good foundation for the smooth study in the future. When reviewing, you should pay attention to the textbook, read the handout, read it repeatedly, recall the teacher's explanation while reading, and understand the contents in the book.

Third, careful observation and hands-on experiments.

Chemistry is a natural subject based on experiments. There are demonstration experiments, students' experiments and students' selected experiments in the textbook, as well as small family experiments. Through these demonstrations and students' experiments, it is the basis of learning chemistry well to learn to observe the operation and phenomena of teachers' demonstration experiments, to learn to do students' experiments independently and to have a good experiment class.

First of all, we should carefully observe the operation and experimental phenomena of every demonstration experiment done by the teacher in class. Chemistry experiment is very vivid and intuitive, and the ever-changing phenomena in the experiment can stimulate students' interest best. However, if students only watch the excitement and don't think about the phenomenon, they won't know what is going on after reading it, which will not help improve their study. Therefore, observation should have a clear purpose. What should be observed clearly before observing the experiment? What is the scope? Solve what problem? This is the purpose of so-called clear observation. Only with a clear purpose can we grasp the key points of observation and observe. Careful and comprehensive observation. For example, the demonstration experiment of hydrogen reduction of copper oxide aims to verify the redox reaction, and copper oxide is reduced to copper by hydrogen. When observing, it is clear that the reactants are colorless hydrogen and black copper oxide powder, the reaction conditions are heating, and the products are water and bright red copper.

Secondly, in order to give students a good experimental class, we must preview before class and make clear the purpose, principle and operation steps of the experiment. When conducting an experiment, do it yourself, don't be a bystander, carefully do every experiment arranged in the experimental content, pay attention to it during the experiment, operate in strict accordance with the experimental requirements, practice the basic operation repeatedly, patiently and carefully observe various phenomena during the experiment, think carefully, and record accurately and truly.

Fourth, expand knowledge.

1. Read chemistry extracurricular books

To learn chemistry well, we should pay attention to reading extracurricular books, such as Chemistry Teaching Reference for Middle School Students, Mathematical Physics for Middle School Students, Inside and Outside the Classroom and other popular science books. Their contents are closely related to the chemistry syllabus and textbooks, and they have strong pertinence and applicability. It is necessary to cooperate with the teaching progress, guide the analysis of problems, pay attention to intellectual development, and pay attention to ability training. They have a wide range of novel themes, rich and colorful contents, short and pithy articles, easy to understand, lively forms and illustrations. It can help students broaden their horizons, expand their knowledge, stimulate their interest in learning, master learning methods, thoroughly understand teaching materials, flexibly use knowledge and cultivate the spirit of exploration. They are good friends of the students.

2. Participate in chemistry extracurricular activities

In my spare time, I actively sign up for extracurricular chemistry interest group activities, do some interesting chemistry experiments, watch some movies and videos about chemistry teaching and popular science, visit factories, participate in the preparation and performance of chemistry evenings, collect and sort out chemistry riddles, and publish chemistry wall newspapers. These activities will make students feel that chemistry knowledge is so rich and colorful, make students have a strong interest and desire in chemistry learning, and urge them to study chemistry hard.

Verb (abbreviation for verb) uses network resources.

Nowadays, with the popularization of computers, many schools and students' families are equipped with computers, and there is a lot of knowledge about chemistry learning on the Internet. Students can use network resources to search for more study materials. At the same time, many websites on the Internet have online learning courses. These courses made by front-line teachers with professional knowledge and teaching experience are all equipped with multimedia teaching courseware. By browsing these courses, students can easily solve the key and difficult problems in their studies.

In short, there is no fixed method for learning, and everyone can make his own learning method according to his own actual situation.