Abstract: Experiment is an indispensable part of chemistry teaching. Demonstration experiment can not only improve teachers' teaching efficiency, but also promote the change of students' learning style and cultivate students' innovative spirit and practical ability.

Keywords: demonstration experiment; Classroom teaching; efficiency

Chemistry is a natural subject based on experiments. Throughout the history of chemical development, it is not difficult to find that the birth of many chemical theories and the discovery of chemical substances are inseparable from chemical experiments, which promote the development of chemistry and chemistry education.

In chemistry teaching, in order to cooperate with the development of teaching content, teachers sometimes need to design and implement experiments by themselves. Such an experiment is a demonstration experiment. Demonstration experiment is an indispensable part of teaching. Many concepts, principles and laws must be developed through experiments and finally demonstrated. It can be said that demonstration experiment is the basis of chemistry teaching, and it is one of the important means for teachers to show the teaching content and students to learn chemistry knowledge and skills.

First of all, think about the role of demonstration experiment.

From the perspective of knowledge and skills, students can easily acquire vivid perceptual knowledge and form accurate chemical concepts through demonstration experiments, so as to better understand chemical reactions and consolidate chemical knowledge. At the same time, demonstration experiments can also promote students' ability to observe, analyze and solve problems.

From the perspective of process and method, students can easily and intuitively understand and master the basic scientific research methods and skills such as the operation process, operation essentials and experimental phenomenon analysis of demonstration experiments by participating in the observation and analysis of the whole process.

Demonstration experiment shows not only the phenomenon of chemical reaction, but also the persistent pursuit of truth and scientific exploration of chemists through the ages from the perspective of emotion, attitude and values. These materials are fresh materials for teachers to educate students on values and outlook on life. Judging from the actual teaching situation, demonstration experiments have also played an important role in stimulating students' curiosity and greatly mobilizing their enthusiasm and initiative.

Second, the types of demonstration experiments

There are two kinds of demonstration experiments: one is verification and the other is inquiry.

1. Verification demonstration experiment

Verify that the teaching mode of demonstration experiment is organized according to the program of problem-conclusion-principle-experiment. Take the entity experiment of redox reaction as an example. First of all, ask the question: what is the essence of redox reaction? Then it is concluded that the essence of redox reaction is the transfer of electrons; Reanalysis principle: the transfer of electrons will inevitably lead to the change of atomic charge of elements, that is, the change of valence of elements, so the transfer of electrons is the essence of redox reaction, and the change of valence is the characteristic of redox reaction; Finally, the correctness of the conclusion is verified by experiments. Verification demonstration experiment is mainly used to confirm the correctness of chemical theory or chemical reaction principle. Experiments such as hydrolysis of high school chemical salts and inference of chemical properties of potassium from sodium metal all belong to this category.

2. Explore demonstration experiments

The teaching mode of inquiry demonstration experiment is organized according to the procedure of problem-experiment-principle-conclusion. Or take the substantial experiment of redox reaction as an example. Firstly, the question is raised, and then a specific redox reaction experiment (such as the reaction between zinc and copper sulfate solution) is designed and implemented, and the experimental phenomena are analyzed. On the basis of clarifying the principle, the conclusion is drawn. The process of exploring and demonstrating experiments is actually a scientific research process of cognitive law and logical thinking. This teaching mode plays an important role in improving students' thinking ability and cultivating students' scientific research literacy. There are many exploratory demonstration experiments in high school, such as the reaction of sodium metal with water and the reaction of ethylene with acidic potassium permanganate solution.

Third, improve demonstration experiments and optimize chemistry classroom teaching strategies

1. The experimental operation should be standardized.

As the organizer of classroom teaching, teachers' understanding, design and operation of experiments will exert a subtle influence on students. Therefore, teachers must pay attention to the influence of this demonstration effect when implementing experiments, which will provide reference for students to design and implement inquiry experiments independently. In addition, students are most sensitive to the teacher's experimental operation process and the phenomena produced during the experiment. In view of this, teachers' experimental operation must be absolutely accurate, which is the premise and guarantee to standardize students' experimental operation and obtain good experimental phenomena. For example, when dissolving solid substances, be sure to make the glass rod move circularly in a certain direction in the beaker, and be careful not to let the glass rod touch the beaker, let alone let the solution splash out of the beaker.

2. Face the experiment and fail

The demonstration experiment conducted by teachers is generally the demonstration experiment required in the textbook. In fact, the demonstration experiments given in the textbook are determined after thousands of choices in terms of operation difficulty, success rate and typicality. These experiments are easy to be successfully implemented for any teacher who has mastered the basic experimental operation skills. However, an experiment is bound to have accidents due to time, place, occasion, weather, drugs, instruments and the physical and mental condition of the experimenter. Once an accident happens, teachers should take remedial measures quickly: first, they should calmly analyze and find out the reasons, instead of making excuses for themselves. We should see that this is an opportunity to guide students to solve practical problems and mobilize students to find the reasons for the failure of the experiment. In the absence of reasons, teachers should frankly admit the failure of the experiment realistically, and can't simply prevaricate students with excuses such as drug failure and instrument failure, let alone fabricate phenomena and practice fraud. Serious and responsible spirit and rigorous scientific attitude can not only cultivate students' style of seeking truth from facts, but also show students the personality charm of teachers.

3. Demonstration experiments should play a demonstration role.

In the chemical demonstration experiment, students should observe the whole process of chemical change through experiments, reflect the authenticity and scientificity of the experimental process and convince them. Therefore, demonstration experiments must play a demonstration role. It is not advisable to act without showing traces or simply turn students' observation of experimental phenomena into teachers' description of experimental phenomena. To realize the function and effect of demonstration experiment, we should focus on the realization of teachers' classroom teaching objectives.

(1) Make full preparations for the experiment before class and make clear the teaching objectives of the experiment. Demonstration experiments are used to cooperate with teaching. Teachers should carefully design experiments according to the teaching content and objectives in the process of preparing lessons. During the experimental demonstration, it is forbidden to carry out experiments at will without purpose. If you experiment for the sake of experiment, it will only make students' understanding float on the surface of the experimental process and make them unable to explore in depth. We advocate the practice of practicing experiments before class, which helps teachers to control the experimental process and effectively prevent accidents such as omissions in experimental design and inconspicuous phenomena. For example, in the reaction experiment of sodium metal with water, in order to verify that alkali is generated in the product, phenolphthalein must be added dropwise before sodium metal is put into water. Although the same phenomenon can be produced by dropping phenolphthalein after the reaction, the experimental effect is greatly weakened.

(2) The operation process is clear and intuitive, which is convenient for students to observe. Demonstration experiment is ultimately for teaching. Teachers can't ignore students' feelings in the process of implementing experiments. In the process of demonstration experiment, measures should be taken to ensure that the experimental phenomenon is obvious, convincing and convenient for students to observe, so as to enhance the experimental effect of demonstration experiment. For example, the projector can be used to solve the problem that students in the back row can't see clearly or can't see clearly the experimental phenomenon, and white paper or colored paper can be used to set off the color change in the reaction process. If the teacher's demonstration experiment can't make students observe the experimental operation and reaction phenomenon conveniently and clearly, such an experiment can only bring thankless results.

(3) Students observe the experimental phenomena accurately and comprehensively. A chemical reaction often involves changes in sound, light, heat, color, state and taste. Teachers should not only pay attention to how they do it, but also pay attention to how they guide students to see it. Guiding students to observe experimental phenomena can be carried out by presupposing questions, which can narrow the scope of students' observation, eliminate the influence of interference factors and make students' observation more targeted. For example, the reaction experiment of sodium and water can ask the following questions to guide students to observe: Where is sodium in water? What is the state of sodium in water? Can you hear anything? Did the color of the solution change before and after the reaction? With these questions to observe the experiment, students' observation will be concrete and comprehensive. After the demonstration experiment is completed, students should also be required to express their reaction phenomena accurately, concisely, concisely and completely, which is an effective method to test and evaluate the phenomena observed by students.

(4) Guide students to analyze the essence of reaction through reaction phenomena and draw conclusions. It is not only a chemical demonstration experiment, but also a work that must be completed in any scientific experiment. Only when this step is completed can the chemical experiment be completed. Without this step, the teacher's demonstration experiment can only be a magic show for students. Of course, the analysis of experimental phenomena is the most complicated, difficult and critical link in chemical experiments. Teachers should play a leading role in this link, not draw conclusions for the sake of conclusions, and it is the most critical to improve students' ability to analyze and solve problems. For example, in the experiment of copper, zinc and dilute sulfuric acid primary battery, students will be surprised by the bubbles on the copper sheet after connecting it with zinc sheet and putting it into dilute sulfuric acid solution. The following teaching core should be that teachers guide students to analyze the composition of gas and its generation principle. After drawing the conclusion that gas is hydrogen and hydrogen ions gain electrons, students will naturally realize that the chemical reaction of the primary battery is only redox reaction, and it is not surprising that the pointer deflects after connecting a sensitive galvanometer.

4. Scientific research method permeates the experimental process and has certain openness.

Teachers should pay attention to demonstrating the scientificity and rationality of experiment implementation, such as the application of observation records, variable control and other scientific research methods during the experiment. In addition, the demonstration experiment should be open to a certain extent. For example, students can replace the teacher's demonstration experiment by role exchange, encourage students to evaluate the teacher's demonstration experiment and put forward reasonable improvement measures. Demonstration experiment is not only a teacher's business, but also a wonderful class with students' participation.

To sum up, to improve the teaching effect of demonstration experiments, the foothold should not only be to complete the experiments required by the teaching materials, but to integrate these experiments into the organic part of teachers' classroom teaching. Strengthening the cultivation of students' practical ability and thinking ability, realizing the improvement of thinking ability, and finally accumulating students' own scientific literacy is the fundamental purpose of demonstration experiment teaching.

References:

[1] summer. Senior high school chemistry curriculum standard teacher reader [M]. Wuhan: Huazhong Normal University Press, 2003.

[2] Yang. My opinion on the demonstration experiment of chemistry [J]. China Science and Education Innovation Guide, 2008(2 1).

Abstract: Experiment is an indispensable part of chemistry teaching. Demonstration experiments can not only improve the teaching effect of teachers, but also have far-reaching positive significance for changing students' learning methods and cultivating students' innovative spirit and practical ability.

Keywords: demonstration experiment; Classroom teaching; effective

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