Teaching objectives
Knowledge target
On the basis of understanding chemical equations, students can master the calculation of the mass of reactants and products;
Through the calculation of chemical reaction, let students understand chemical reaction from a quantitative point of view and master the problem-solving format.
capability goal
Through the calculation of chemical equations, cultivate students' ability to examine questions, analyze problems and solve problems.
Affective goal
Through the calculation of relevant chemical equations, students are trained to apply what they have learned and integrate with practice, and at the same time, students are trained to realize that qualitative and quantitative research on substances and their changing laws are complementary, and quality and quantity are dialectical unity.
Teaching suggestion
Textbook analysis
According to the chemical equation, beginners should strictly follow the five-step method and writing format in the textbook. That is, ① set an unknown number; ② Write the equilibrium chemical equation according to the meaning of the question; (3) Write the molecular formula quantity, known quantity and unknown quantity of the substance; (4) column ratio, solving; 5 answer the question. Doing so can form good study habits.
To solve this problem, we need to have a clear understanding of chemical knowledge in chemical calculation problems, that is, chemical equations can be written correctly according to the meaning of the problem. If the chemical formula of a substance in the chemical equation is wrong or unbalanced, even if the mathematical calculation is accurate, the correct result will not be obtained. It can be seen that correctly writing and balancing chemical equations is the key factor to successfully solve the calculation problem of chemical equations.
Chemical calculation problem is a comprehensive application of multidisciplinary knowledge based on chemical knowledge and using mathematics as a tool. It is necessary to have a chemical thinking method and a solid mathematical foundation.
To solve the calculation problem of chemical equations, we must first carefully examine the questions, make clear the requirements, and set unknown quantities to avoid blindness. The second is to express the chemical changes given in the title with chemical equations. Find out the known quantity according to the meaning of the question. Then follow the steps to solve the problem. At the same time, we should overcome psychological negative factors, don't be afraid of chemical calculation, and believe in ourselves. Students with poor foundation should first do some simple calculation problems about chemical equations and gradually realize the process of organic combination of mathematical calculation methods and chemical knowledge. Then do more difficult questions. Students with a good foundation should have the ability to solve difficult problems. In junior high school, it is easy to solve a linear equation with mathematical column proportion formula, that is, to set an unknown number and an equality relationship. For moderately difficult problems, knowledge of solving binary linear equations and ternary linear equations is often needed. The difficulty of the calculation process has not increased much, but there are many steps and it is a little more troublesome. The difficulty mainly lies in how to set a number of unknowns and find out the "quantity" relationship between these unknowns. In a word, we should strengthen the training of chemical calculation according to our own chemical knowledge and mathematical knowledge level, so as to master the ideas and methods of solving problems in chemical calculation skillfully.
Teaching suggestion
This section only requires students to learn the calculation of pure matter, and does not involve unit conversion. The calculation is based on students' understanding of the meaning of chemical equations, including how many products can be obtained at most by a certain amount of reactants; And the significance, how many reactants are needed to make a certain amount of products. Therefore, the meaning of chemical equations should be combined with calculation in teaching.
Chemical calculation includes chemistry and mathematics, in which chemical knowledge is the basis of chemical calculation and mathematics is the tool of chemical calculation. Students are required to master relevant chemical equations, such as the correct writing and balancing of chemical equations. In teaching, teachers should demonstrate the problem-solving format for students, deepen the understanding of the meaning of chemical equations through the calculation of chemical equations, cultivate students' good habit of thinking according to chemical characteristics, further cultivate students' ability of examining questions, analyzing and calculating, and at the same time make students realize that quantitative and qualitative research on substances and changing laws are complementary, and quality and quantity are unified dialectical views. In this class, we can combine lectures with practice, mobilize students' enthusiasm, broaden their thinking, improve their problem-solving skills, cultivate their thinking ability and deepen their knowledge and understanding of chemistry through exercises from easy to difficult and training with multiple solutions to one problem.
Teaching design scheme
Emphasis and difficulty: Find the quality of product (or reactant) from the quality of a reactant (or product).
Teaching process:
Introduction: Chemical equation can be expressed as the change of the relationship between substance and mass before and after chemical reaction. Then, in chemical industry, agricultural production and real life, how to calculate the quality of products and raw materials through the quality relationship, make full use of it and save energy? In this lesson, we will learn to calculate according to chemical equations, which is a method to study the change of matter quantitatively.
Projection: for example 1, write the chemical equation _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _. Write _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _. 32g sulfur can be completely burned in sufficient oxygen to generate _ _ _ _ _ _ _ grams of sulfur dioxide. 1.6 grams of sulfur can be completely burned in sufficient oxygen to generate _ _ _ _ _ _ _ _ grams of sulfur dioxide, and at the same time, the consumed oxygen quality is _ _ _ _ _ _ _ _ _.
Discussion completed:
S+O2 ignites SO2
32 32 64
For every 32 parts of sulfur and 32 parts of oxygen, 64 parts of sulfur dioxide will be produced.
32 grams 64 grams
1.6 g 3.2 g
Student exercise 1: Write the chemical equation of complete phosphorus combustion _ _ _ _ _ _ _ _ _ _ _ _ _ _ _. Calculate the mass relationship between substances _ _ _ _ _ _ _ _. At present, 3 1g white phosphorus is completely burned, and it takes _ _ _ _ _ _ _ grams of oxygen to generate _ _ _ _ _ _ _ _ grams of phosphorus pentoxide.
Summary: According to the chemical equation, the mass ratio of each substance can be obtained; According to the mass ratio between substances, the mass of unknown substances can be calculated from the mass of known substances. This process is the calculation of chemical equations.
Writing on the blackboard: the third section is calculated according to the chemical equation
Projection: Example 2 1 1.6 grams of potassium chlorate can be decomposed by heating. How many grams of oxygen can be obtained?
Write on the blackboard: Solution: (1) Set the unknown number according to the meaning of the question; Let the available oxygen mass be x.
(2) Write chemical equations; 2 kclo 3δ2 KCl+3 O2↑
(3) List the molecular formula quantities and known quantities of related substances; Unknown quantity 245 96
1 1.6 g x
(4) Column proportion formula, and find the unknown quantity 245/11.6g = 96/x.
x = 96× 1 1.6g/245 = 4.6g。
(5) A: A: You can get 4.6 grams of oxygen.
Students practice and a classmate performs on the blackboard.
Projection:
Student Exercise 2: How many grams of potassium permanganate does the laboratory need to get 3.2 grams of oxygen? How many grams of manganese dioxide are produced at the same time?
Exercise 3 How many grams of copper oxide does it take to reduce copper oxide with hydrogen to get 1.6 grams of copper?
Analysis, discussion and summary:
Discussion: 1. If the chemical equation is unbalanced, will it affect the calculation results?
2. In the calculation of chemical equations, can impure known quantities be brought into the calculation of chemical equations?
Projection: Example 3:12.25g of potassium chlorate and 3g of manganese dioxide are mixed, heated and completely reacted, and how many grams of oxygen are produced? How many grams of solids are left after the reaction?
Students' exercise: Ask each other questions at the same table, exchange answers, and the teacher will discuss and check.
Question type (1) calculates the quality of products by knowing the quality of reactants.
(2) By knowing the quality of products, we can find out the quality of reactants.
Summary: According to the calculation requirements of chemical equations
The chemical equation should be balanced.
It is necessary to replace equations with scalars.
Relationship with relational quantity
The unit of calculation cannot be forgotten.
The proportion between relational quantities
Remember to solve problems instead of answering them.
Blackboard design:
The third quarter according to the calculation of chemical equation
Example 2. How many grams of oxygen can be obtained by heating and decomposing 1 1.6 grams of potassium chlorate?
Solution: (1) Set the unknown quantity according to the meaning of the question; Let the available oxygen mass be x.
(2) Write chemical equations; 2 kclo 3δ2 KCl+3 O2↑
(3) List the molecular formula quantities and known quantities of related substances; Unknown quantity 245 96
1 1.6 g x
(4) Column proportion formula, and find the unknown quantity 245/11.6g = 96/x.
x = 96× 1 1.6g/245 = 4.6g。
(5) Answer: 4.6 grams of oxygen can be obtained.
Summary: According to the calculation requirements of chemical equations
The chemical equation should be balanced.
It is necessary to replace equations with scalars.
Relationship with relational quantity
The unit of calculation cannot be forgotten.
The proportion between relational quantities
Remember to solve problems instead of answering them.