Chemistry： Reconstructing Knowledge and Methods

　　The educational function of chemistry course is mainly reflected in four aspects: first, to impart basic concepts and key abilities and to discriminate scientific facts; The second is to enlighten scientific thinking and methods and solve real problems; Third, cultivate scientific spirit and quality, and understand the value of disciplines; Fourth, carry forward the patriotic spirit and establish a sense of responsibility and mission to serve the motherland. As a key link in education, the college entrance examination must also implement the fundamental task of cultivating people by virtue, give play to the correct educational orientation of the examination, and give play to the core functions of cultivating people by virtue, selecting materials for service and guiding teaching.

　　Change ideas and jump out of the cycle

　　Looking back over the years, the real questions of the national chemistry college entrance examination are mostly around the major themes of the times and the frontier achievements of chemistry in social life, carefully selecting situational materials such as daily life, production and environmental protection, academic exploration and experimental exploration, focusing on the main contents of the subject, innovating the presentation methods of test questions and information, and highlighting the examination of information sorting ability, critical thinking ability, dialectical thinking ability and language expression ability, which not only examines students’ academic accomplishment and key ability, but also gives play to the educational value and role of chemical science.

　　The common problems in the review process of senior three in general schools are "four stresses and four despises": attaching importance to teaching AIDS and neglecting teaching materials; Pay more attention to knowledge than thinking; Emphasis on answers, light process; Re-explain, light experience. Especially in the last month before the exam, many teachers often adopt the mode of "practice+comment" and "exam+comment", which leads to the boring and ineffective state of students desperately brushing questions and teachers correcting and explaining, leading to physical and mental fatigue and anxiety of teachers and students.

　　In the final review stage, chemistry teachers should change their ideas and jump out of the cycle of "practice+lecture+examination". Through in-depth research on the real questions of college entrance examination, tracing back to the source, and linking the key topics, hot knowledge topics and innovative functional test questions through "theme", the textbook knowledge and problem-solving methods are reconstructed, so that students can build their own knowledge topics and find the focus and breakthrough points of review.

　　Grasp the main content

　　The main contents of high school chemistry include basic concepts and research methods, material structure and properties, chemical reaction principle, preparation and application of inorganic substances, experimental basis and scientific inquiry, organic synthesis and application. Linking textbook topics through themes is to consciously combine the knowledge of each major section to make them interrelated and mutually confirmed. The teaching theme is constructed by creating situations, which makes the original knowledge in students’ minds modular and functional, and promotes the synchronous improvement of students’ knowledge and ability. For example, when reviewing the related contents of salt hydrolysis and weak electrolyte ionization, the following teaching flow can be designed:

　　Summarize the learned hydrolysis reaction → the basic form of salt hydrolysis reaction → understand that it is weak to hydrolyze from the perspective of double decomposition reaction → take CH_3COONa as an example to analyze the relationship between the hydrolysis equilibrium constant of CH_3COOH and the ionization equilibrium constant of CH_3COOH → the weaker it is, the more hydrolyzed it is → analyze the acidity and alkalinity of the mixed solution with the same concentration of ch _ 3cooh and CH_3COONa by combining the equilibrium constant. The acidity and alkalinity of the mixed solution of HCN and NaCN with the same concentration → the comparison of ion concentrations in the two groups of solutions → the analysis of the acidity and alkalinity of the solutions of NaHCO_3, NaHSO_3 and KHC_2O_4 and the concentration of related particles combined with equilibrium constants.

　　When reviewing elemental compounds, students should be guided to understand the properties of elements, their simple substances and compounds with their structures and principles. For example, it emphasizes the influence of chemical bonds and intermolecular forces on the properties of matter, and establishes a channel between micro and macro through the forces; Design a teaching theme with change view under the guidance of balance thought, and deeply understand elements and their compounds, electrochemistry, energy, equilibrium movement and other issues; This paper analyzes chemical phenomena and problems from macro and micro levels as well as qualitative and quantitative perspectives.

　　Generally, the test questions of chemical reaction principle take continuous reaction or parallel reaction (competitive reaction) in industrial production as situational material, and mainly examine enthalpy change (material accounting, energy accounting and economic accounting), chemical equilibrium constant (the problem of material equilibrium transformation), chemical reaction rate and industrial production safety, and mainly analyze it from two angles of balance and rate. The chemical equilibrium is calculated with the equilibrium constant as the core, and the chemical rate mainly analyzes its influencing factors, and finally returns to the temperature for adjustment. For example, in electrochemical review, students should focus on the ionic behavior in electrolyte solution.

　　In the review of experimental chemistry, it is best to choose the preparation of substances to design thematic teaching, because this is the most complete process. Let students fully understand the purpose, method, result and conclusion of the experiment. The core is separation and purification, the focus is on the operation specification, and the difficulty is the principle behind the operation. This requires students to learn from and use the basic experimental methods in middle school chemistry according to the basic principles of the experiment, give priority to the analysis of the material system as the first element of the experiment, and fully consider the restrictive conditions such as experimental equipment and drugs, experimental requirements, experimental safety, tail gas treatment, method selection and other issues to complete the design, analysis or evaluation of the chemical experiment.

　　Cause analysis of wrong questions

　　In the review teaching, in addition to the above topics, we can also carry out the theme teaching of students’ wrong questions and cause analysis. From the perspective of problem solving, subject core literacy is the comprehensive quality and key ability of students in the process of solving real, meaningful, complex and even unpredictable situational problems by using the knowledge and skills obtained from subject courses. In teaching activities, guiding students to carry out comprehensive analysis, practice model cognition and evidence reasoning according to the knowledge of material structure and nature, basic concepts and basic principles in real problem situations can promote the development of students’ understanding of chemical problems, and then realize the development from chemical subject knowledge to chemical core literacy. The selected related questions should be more exploratory, active, practical, open and hierarchical, so as to fully reflect its function of improving students’ comprehensive ability to use chemical knowledge to solve practical problems. In the process of analyzing test questions, we should analyze students’ answers, especially the language expression, thinking and standardization of answering questions, refine students’ feedback, make full use of feedback information, sort out difficult questions, find deep-seated reasons, check for missing items in time, and construct theme teaching through model analysis of test questions to improve review efficiency. (Zhou Xuegong, a researcher and senior teacher of Haining Teacher Training School, Zhejiang Province)