Paper Keywords: high school chemistry inquiry experiment safety and environmental protection

The new curriculum reform requires us to let students experience the process of scientific research, stimulate their interest in learning chemistry, strengthen their awareness of scientific inquiry, promote the change of learning methods, and cultivate their innovative spirit and practical ability in practice. However, in the experimental exploration, there are many hidden dangers in the experiment, which are often easily overlooked. In this paper, the experimental safety cases and the cultivation of students' awareness of experimental environment in high school chemistry inquiry experiment teaching are effectively analyzed.

There are nearly 170 chemical experiments in middle school chemistry textbooks, most of which belong to the preparation and property experiments of toxic, flammable and explosive substances. At the same time, environmental education can penetrate many industrial production processes such as sulfuric acid, nitric acid, synthetic ammonia industry, ironmaking, steelmaking, electrolysis and electroplating. In the teaching of each chapter, it is necessary to strengthen the infiltration of environmental education, explain the generation and harm principle of pollution sources from the perspective of chemistry, so that students can know why, understand the causes of harm and protective measures in principle. For example, when it comes to water pollution, it should be emphasized that the pollution sources of water pollution are mainly the arbitrary discharge of industrial wastewater containing metal ions and the use of pesticides. Common heavy metal ions are barium ion, mercury ion, copper ion and chromium ion. These heavy metal ions can coagulate protein in organisms, and once the water containing these heavy metal ions is drunk by people, it will coagulate hemoglobin which transports blood in the human body, leading to hypoxia, suffocation and death.

First, the analysis of common experimental safety cases in high school chemistry inquiry experiment teaching

(a) in violation of operating procedures.

Case 1: The purity must be checked before igniting hydrogen. However, if you are in the demonstration experiment of hydrogen production by the reaction of zinc and hydrochloric acid, after the reaction of zinc particles, open the plug of the reactor and put zinc particles on it, the plug will ignite, leading to the explosion of the instrument. Why did the explosion happen? This is because you have violated the operating regulations that you must check the purity of hydrogen before ignition. During the experiment, the plug was opened and zinc particles were filled, which was the same as the zinc particles at the beginning of the experiment. Air enters the reactor, hydrogen and oxygen are mixed and ignited, and it will explode.

Case 2: When making ethylene, alcohol and concentrated sulfuric acid are poured into a large test tube, and when heated, the liquid will be ejected. In order to prevent such accidents, when heating liquid to make gas, tiles should be attached to prevent explosion and boiling. It should also be noted that if ethylene is made by heating alcohol and concentrated sulfuric acid with ceramic tiles, after the collection is completed by drainage and pumping, the alcohol lamp is first removed, and cold water flows into the flask filled with concentrated sulfuric acid along the conduit, causing the flask to burst. This is because you violated the experimental operation. Heat the gas and collect it by drainage. After the experiment, the catheter should be pulled out of the water first, and then the alcohol lamp should be removed. The above operation is just the opposite. The alcohol lamp was removed first. Before taking the catheter, water flowed into the reactor along the catheter, causing the instrument to burst and sulfuric acid to overflow.

(2) Accidents caused by overdose.

Although some experiments are strong, small doses are not dangerous, and small doses of drugs will be dangerous.

Case 3: Red phosphorus burns in oxygen, and the reaction is fierce, but there is no danger when the dosage is small. When doing grouping experiments, let students observe the burning phenomenon of red phosphorus in oxygen. The dosage must be moderate, and drugs should not be used at will, otherwise accidents will occur.

Case 4: When preparing silver ammonia solution, if excessive ammonia water is added, it will be reused after a long time, and explosive substances will be generated in the solution, which will lead to explosion accidents when used. In order to prevent excessive ammonia from being added in this experiment, silver ammonia solution must be used together and cannot be left for a long time.

Case 5: Copper reacts with hot concentrated sulfuric acid and copper reacts with nitric acid. Try to control the amount of reactants, as long as the correct and obvious results can be obtained, students can observe the existence of their substances and understand and master their properties.

(3) Drugs are mixed with impurities.

Case 6: When the mixture of potassium chlorate and manganese dioxide is heated to generate oxygen, charcoal powder is mistakenly added into the test tube as manganese dioxide and mixed with potassium chlorate, so that the medicine is mixed with impurities and an explosion accident is caused. Therefore, when using drugs, we should carefully identify the drugs and don't do it carelessly.

Case 7: When doing methane demonstration experiment, someone ignited methane gas without exhausting all the air, which led to an explosion accident. In this experiment, the properties of methane should be tested first, and then methane gas should be ignited to prevent air from mixing, ensure the purity of methane and avoid explosion accidents.

(four) the use of lost labels without identification of the reagent accident.

Case 8: When preparing the solution, sulfuric acid was mistaken for hydrochloric acid, causing injury accidents. Any reagent with missing label must be tested and determined before use to avoid injury accidents.

(5) The air in the laboratory is not circulating.

Case 9: When demonstrating toxic gases such as chlorine, hydrogen sulfide, nitrogen dioxide and carbon monoxide, or when students do experiments with combustible gases. Such as hydrogen, ethylene, acetylene, etc. If the air in the laboratory is not circulated, toxic and flammable gases will escape into the air and accumulate to a certain concentration, which will cause poisoning of teachers and students or other accidents. Therefore, the laboratory should be equipped with ventilation facilities such as fume hoods and ventilation fans, and air circulation must be realized in the laboratory.

Second, the cultivation of students' experimental safety and environmental awareness? Teachers are the main implementers of education for students. Teachers' thoughts, words and deeds have the most direct and effective influence on students. From the perspective of cultivating "safety awareness", teachers should do the following:

(1) Detailed demonstration experiments.

Teachers' every move in demonstration experiments directly affects students' attitudes and methods in hands-on experiments. Therefore, even the most commonly used instruments should not be used casually. For some experiments with hidden dangers, we should fully prepare lessons and guide students to think through unsafe factors.

(2) Rational use of counterexamples.

For the consequences of some wrong operations that can be simulated in the laboratory, teachers can design some wrong counterexamples to verify and deepen students' impression. If impure combustible gas ignites and explodes, water is poured into concentrated H? 2SO？ The consequences of dilution are 4; When heating, turn off the alcohol lamp first, which leads to the backflow of water and the explosion of the test tube. As long as conditions permit, the device design is reasonable, and it can be tried without causing accidents.

(3) Strict supervision to cultivate students' good experimental habits.

The students were most impressed when they entered the laboratory. The age characteristics of middle school students determine that they are curious about everything, and being active is their nature. Therefore, in students' experiments, in addition to clearly standardizing the operation and safety requirements, strengthening supervision is also an essential link.

(4) Enhance awareness of prevention and cultivate self-help ability.

For example, how to deal with strong acid and alkali splashing on you, and how to deal with and save yourself in an emergency.

(5) Using video experiment to assist teaching is authentic.

For some complex, dangerous, demanding and long-term experiments that are not suitable for classroom demonstration, shoot and play them in class. This not only ensures the authenticity and intuition of the experiment, but also facilitates the observation of experimental phenomena and improves the classroom density.

Case 10: Speaking of "carbon reducing carbon dioxide", many students can hardly imagine how this reaction experiment was done. After many experiments, I decided to use iron pipe as the reactor for reducing carbon dioxide with charcoal, and then made the experiment into a 2-minute video, bringing a complicated experiment with a long reaction time to class, which played a very good role. Secondly, in order to improve the experimental teaching, when making some toxic substances (gas and liquid), we should constantly improve the experimental device to avoid gas escape or liquid leakage. For harmful tail gas, absorption or conversion devices should be added, and it is not allowed to be discharged into the atmosphere at will. Such as sulfur dioxide, hydrogen sulfide, nitrogen dioxide, chlorine and other toxic gases, tail gas can be absorbed by alkali solution (such as sodium hydroxide solution).

Third, harvest and reflection

To sum up, as long as we know the causes of all kinds of chemical experiment accidents, follow the operating rules and operate carefully, we can avoid all kinds of accidents and make the experiment safe. In the experimental operation, students should also be educated to strictly abide by the operating rules to prevent students from playing around for fun. Students are required to use a small amount of reactants to make a small amount of toxic substances when making toxic gases, so as to minimize pollution. The key of safety experiment is to carry out the experiment according to the operating rules, and the danger can also become safe. On the contrary, security becomes unsafe. But don't be afraid, and don't be afraid to experiment with fear; Be familiar with the operation rules, understand the reaction rules, ask questions if you don't understand, and don't be reckless. Otherwise, once an accident happens during the experiment, it will endanger the safety of teachers and students, even cause serious disability and lifelong misfortune, and affect students' interest in learning chemistry, which is of great significance and must be highly vigilant.

refer to

[1] On the safety problems in chemical experiment teaching

[2] Xia. Senior high school chemistry curriculum standard teacher reader [M]. Wuhan: Huazhong Normal University Press, 2003: 44-46.

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