First of all, talk about textbooks.

This lesson is the first lesson of the fifth unit project 1 "law of conservation of quality" in the ninth grade of compulsory education curriculum standard, including the meaning, reason and application of the law of conservation of quality.

1, the position and function of teaching materials

The law of conservation of mass is an important chemical law in junior middle school chemistry, and it is the theoretical basis for analyzing the relationship between matter and mass in chemical reactions. Its application runs through the whole middle school chemistry. This textbook plays a connecting role in junior middle school chemistry. Before that, students learned the basic knowledge of element symbols, chemical formulas, molecules and atoms, and had a certain understanding of the qualitative change of substances in chemical reactions. The teaching of this course will guide the students' understanding of chemical reaction from "quality" to "quantity", and also lay a theoretical foundation for the teaching of writing and calculation of chemical equations, so the content of this course is not only a key point of this unit, but also one of the key points of chemistry teaching in the whole middle school.

2. Teaching objectives

According to the spirit of the new curriculum standard, the intention of compiling teaching materials, the characteristics of this section, the cognitive level and psychological characteristics of junior three students, the teaching objectives of this section are determined as follows:

(1) knowledge and skills:

Make students understand the law of conservation of mass and the reasons for conservation, and learn to explain and solve some chemical phenomena and problems with the law of conservation of mass.

(2) Process and method:

Through experiments and analysis, cultivate students' ability to discover and explore problems through experiments.

Through the analysis of the nature of chemical reaction and the reason of mass conservation, students' logical reasoning ability is cultivated, so that students can understand the basic ideas of studying chemical problems.

(3) Emotion, attitude and values:

L through inquiry learning, cultivate students' scientific attitude of being good at cooperation, being brave in exploration and being rigorous and realistic. Educate students with dialectical materialism to understand the essence of things through phenomena.

3. Teaching emphases and difficulties

Teaching emphasis: understanding the meaning of the law of conservation of mass

Teaching difficulties: how to guide students to draw conclusions through experimental exploration, how to make students understand the reasons of mass conservation, and thus understand chemical reactions from a quantitative perspective.

4. Improvement of teaching materials

The first scheme of P88 activity and exploration in the textbook requires high operation: after the glass tube is heated, it should be inserted into the conical bottle quickly and just contact with the white phosphorus in the bottle, which is easy for students to have such questions: Is there any exchange of gas inside and outside the bottle during the insertion? For this reason, I made the following adjustments: instead of igniting the white phosphorus with a glass tube, I put a balloon around the bottle mouth, and then heated the conical bottle on the asbestos net until the white phosphorus completely spontaneously ignited.

The operation of the second textbook scheme is easy to cause students' questions, such as whether water will evaporate, whether air will dissolve in liquid and so on. In this regard, I changed the small beaker into a conical bottle and put a balloon on the bottle mouth, so that students can clearly see that there is no material exchange inside and outside the bottle before and after the reaction, which makes the experimental operation process more rigorous and scientific and draws convincing experimental conclusions.

Second, oral teaching methods

Dostoevsky, a great German educator, said, "Scientific knowledge should not be taught to students, but should guide students to discover them and master them independently." Before learning the content of this lesson, students' chemical knowledge and understanding of chemical inquiry learning methods belong to the enlightenment stage. If the inquiry process does not conform to students' existing cognitive level and psychological characteristics, it will not only fail to achieve the ideal inquiry effect, but also dampen students' enthusiasm for participating in inquiry learning. Therefore, in this class, I use the method of students' independent inquiry and discussion under the guidance of teachers.

Third, theoretical study.

1. Analysis of learning situation

(1) Students' knowledge status: They have learned the essence of element symbols, chemical formulas and chemical reactions, and have mastered some simple chemical reactions.

(2) Students' ability: They have mastered the basic operation skills of simple chemical experiments, but their understanding of chemistry inquiry learning methods is still in the enlightenment stage.

(3) Students' psychological state: Students are just beginning to learn chemistry and are in a state of excitement and curiosity. I firmly grasp this.

2. Guidance on learning methods

(1) experimental inquiry method: learn how to find problems, analyze problems, solve problems, acquire knowledge and cultivate abilities in scientific inquiry.

(2) Cooperative learning method: through cooperative inquiry, cultivate students' awareness of cooperation and mutual assistance.

As Dostoevsky, a great German educator, said, "A poor teacher can only contribute, while a good teacher teaches students to discover the truth".

Fourth, talk about the teaching process

1. The teaching process is designed as follows:

2. Teaching process

(1) Create situations and cause problems.

1. The burning of candles raises the question "What will happen to the quality of substances in chemical reactions?" Then it introduces the research of three chemists, focusing on lavoisier's research and experimental principles. Then put forward the second question, "Is the total mass of all chemical reaction reactants equal to the total mass of products?" Two exploratory experiments are put forward: ① measuring the mass change of candles before and after burning; ② Explore the quality change of magnesium rod before and after burning in air. Under the guidance of teachers, students are divided into groups to carry out exploratory experiments.

Design intention: Let students experience the experiment in the problem situation created by teachers and feel the relationship between quality changes, which is exactly what the new curriculum advocates.

Question 3: "What conclusion do you draw about the relationship between the mass changes of substances in chemical reactions?" Students may have three conjectures: ① the total mass becomes smaller after chemical reaction; ② The total mass becomes larger after chemical reaction; ③ The total mass remains unchanged after chemical reaction. "Is it true?" Enter the second process.

(2) experimental inquiry and guiding discovery

(1) Determine the content of the inquiry.

In order to reduce the blindness of inquiry, students should be guided to determine the contents of inquiry first.

Exploratory experiment 1: mass change of white phosphorus before and after combustion in air.

Exploratory experiment 2: Quality changes of nails and copper sulfate solution before and after reaction.

② Design the experimental scheme

Because students don't understand the chemical reaction principle of these two inquiry experiments, so explain the principle first. Then provide students with the following experimental instruments and drugs, let students choose independently, and design and explore experimental schemes in groups.

③ Experiment, analysis and discussion in groups.

Experimental instruments and drugs:

Inquiry experiment 1: balance, 250mL conical flask, 250mL beaker, alcohol lamp, tweezers, tripod, asbestos net, balloon, sand and cut white phosphorus;

There may be two kinds of schemes designed by students for inquiry experiment 1: the main difference is whether the reaction container is open or closed. After the students conducted experiments on the two schemes respectively, it was found that the product quality of the first scheme became greater. The product quality of the second scheme remains unchanged. "Which scheme has the correct conclusion?" Ask the students to evaluate the plan.

Design intention: By stimulating students' thinking conflicts and their strong desire to explore, not only can students' design interest be enhanced, but also their active thinking can be mobilized.

After discussion, it is concluded that the first scheme is flawed, because the air quality of white phosphorus re-entering the open container after combustion is not considered, so the conclusion that the product quality becomes larger is inaccurate; The second scheme is carried out under closed conditions, and there is no material exchange inside and outside the container during the whole operation. The experimental process is rigorous and scientific, and the conclusion is convincing.

Exploratory experiment 2: balance, conical flask, balloon, nail, copper sulfate solution.

For the design of inquiry experiment 2, students may also have two main types of schemes: the main difference is whether the reaction container is open or closed. The result of both schemes is that the product quality remains unchanged. Through discussion, it is concluded that the quality error caused by evaporation of reaction water at room temperature can be ignored.

The common result of the two inquiry experiments just now is that the quality remains unchanged before and after the reaction. "Why?" This is the difficulty that students understand, so I use animation simulation to break through the difficulty, that is, to enter the third process.

(3) Animation simulation and difficulty breakthrough

The microscopic process of white phosphorus burning in air is simulated by animation, which directly shows that the species, quantity and quality of atoms in chemical reaction must remain unchanged. So it is concluded that all chemical reactions follow the law of conservation of mass.

Design Intention: Students design and successfully try experiments, draw conclusions, experience the fun of learning, understand that scientific experiments need to be rigorous, and actively construct their own cognitive system.

Then he asked, "Why does the mass of candles become smaller after burning in the air and the mass of magnesium rods become larger after burning in the air?" Through discussion, students realize that when analyzing chemical reactions with the law of conservation of mass, remember not to ignore the implicit substances such as gas entering or leaving in the reaction.

(4) Combine with practice and apply what you have learned.

(1) 100 g water and100g alcohol are mixed, and the mass is equal to 200 g. Does this conform to the law of conservation of mass? Why?

② After potassium permanganate is heated in air, the solid mass decreases. Some people say that this fact does not conform to the law of conservation of mass. Are you right? Why?

(3) It is known that 12 g charcoal and 32 g oxygen have just completely reacted, and the mass of carbon dioxide is _ _ _ _ _ g; If 6g carbon is completely burned in 18 g oxygen, carbon dioxide _ _ _ _ g is generated, and the remaining _ _ _ _ _: _ _ _ _ _ g, why?

The question 1 is intended to emphasize that the law of conservation of mass only applies to chemical reactions; The second problem once again highlights the conservation of the total mass of reactants and products; Question 3 aims to help students discover the meaning of the word "participation" in the law of conservation of mass.

Design intention: Through interlocking and progressive problems, strengthen the key knowledge of this lesson and exercise students' ability to solve practical problems and language expression.

(5) class summary

What knowledge have you gained through the study of this topic? What kind of chemistry learning methods have you learned?

Verb (abbreviation of verb) Reflections on Teaching Design

The teaching design of this lesson mainly adopts the teaching form of teacher's guidance, student-centered, teacher-student cooperation, experiment-based and thinking-oriented, focusing on two forms of expression and four highlights.

1.

(1) embodies the teaching concept of quality education in the new curriculum reform;

(2) The learning style that reflects students' independent inquiry.

2. Four highlights

(1) Guide scientific discovery based on experiments;

(2) Taking thinking as the core, carrying out problem inquiry;

(3) Take students as the main body and promote the internalization of knowledge;

(4) Create a research atmosphere in groups.

Six. Blackboard design:

Unit 5 Subject 1 Law of Conservation of Mass

1. Law of Conservation of Mass: In a chemical reaction, the total mass of substances participating in the reaction is equal to the total mass of substances generated after the reaction.

Second, the microscopic essence of the law of conservation of mass-three invariants

The types of atoms remain unchanged; The number of atoms remains unchanged before and after the chemical reaction; The mass of the atom remains the same.

Third, application

After burning, the ash content of paper is less than that of base paper. Why?

Why is the mass of white product greater than that of magnesium belt after combustion?

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