Version 1
First, review the test questions
Classification of substances in high school chemistry
Try to talk about this topic.
1. Title: Classification of substances
2. Contents:
A system obtained by dispersing one (or more) substances in another (or more) substances is called a dispersion system. The former belongs to dispersed substance and is called dispersoid; The latter plays the role of containing dispersoids and is called dispersant. According to the state of dispersoid or dispersant (gas, liquid and solid), there can be nine combinations between them (as shown in Figure 2-4).
When the dispersant is water or other liquid, the dispersion system can be divided into solution, colloid and suspension according to the size of dispersoid particles. Solute particles in solution are usually smaller than 1nm, and particles in suspension are usually larger than 100nm. The colloidal particle size between them is between 1 ~ 100nm.
If we investigate the stability of three dispersion systems: solution, colloid and suspension, we will find that the solution is the most stable. No matter how long it is stored, the solute will not automatically separate from the solvent under normal circumstances; The turbid liquid is very unstable, and the dispersoid will settle under the action of gravity, for example, the sediment entrained in the river will gradually settle; Colloid is between the two and can exist stably under certain conditions, belonging to metastable system.
Some liquid colloids are also transparent, and it is difficult to distinguish them from the solution with the naked eye. So, in what way can we distinguish them?
3. Basic requirements:
(1) needs appropriate situation creation.
(2) There should be classroom interaction in the teaching process.
(3) Please complete the trial lecture in ten minutes.
Defense topic
1. Are all metal oxides basic oxides?
2. Talk about the role of experiment in teaching.
Second, the analysis of test questions
teaching process
Link 1: Introducing a new lesson
The teacher asked junior high school students to learn the classification of substances, so according to the types of substances, how can substances be classified?
Students' answers are divided into pure objects and mixtures.
Can the teacher's questions be further classified?
Students answer that pure substances can be divided into simple substances and compounds.
Before the teacher's guidance, I mainly studied the further classification of pure substances. Today, I will study the further classification of mixtures.
Link 2: New Curriculum Teaching
The teacher's questioning mixture is usually formed by dispersing one substance or several substances into another substance or several substances. We call such a system a decentralized system. Look at the textbook to find the concept of decentralized departments.
Students answer that the system formed by dispersing one substance or several substances into another substance or several substances is called dispersion system.
Put forward questions and combine the concepts of dispersion system, dispersion and dispersant. What are the dispersions and dispersants of copper sulfate solution and muddy water?
Students answer that in the dispersion system, the dispersed substance is dispersoid, and the substance that disperses other substances is called dispersant. Solute dispersion in the solution is copper sulfate solid, and dispersant is water; The dispersoid in the suspension is mud and the dispersant is water.
According to the state of dispersant and dispersoid (gas, liquid and solid), there are several combinations of dispersant and dispersoid, and specific examples are given.
Students answer Qi Qi (air); Liquid gas (cloud); Solid gas (dust); Gas and liquid (foam); Liquid (wine); Solid liquid (muddy water); Gas-solid (sponge); Liquid solids (pearls); Solidify (an alloy). Dispersed outside the bracket, dispersant inside the bracket.
Question: Can dispersion systems be classified according to the size of dispersoid particles?
Students answer that the dispersion system is divided into solution, colloid and suspension according to the size of dispersion particles.
Ask questions and filter Fe(OH)3 and muddy water respectively. Observe and record what you see. What does this mean?
The students answered that the dispersion of colloid can pass through the pores of filter paper, but the dispersion of suspension can't, indicating that the dispersion particles of suspension are larger than those of colloid.
Put forward questions, and consider the relationship between the Dindar effect of colloid and the size of colloid particles, and whether colloid can emit light, combining the experiment just done and the content of the textbook History of Science.
Students answered that the wavelength of visible light is between 400~700nm, and the diameter of colloidal particles is between 1 ~ 65438+400 ~ 700nm, which is less than the wavelength of visible light and can scatter light waves. When the light beam passes through the colloid, the light beam is scattered by the colloid particles, not by the colloid particles themselves.
Ask questions and think about why there is no bright "path" for light to pass through solutions and turbid liquids.
The students answered that light scattering also occurs in the solution, but the scattering is very weak because the diameter of the particles in the solution is less than 1nm. Therefore, the Tindal effect can be observed when the beam passes through the colloid, but not when it passes through the solution.
Link 3: Expand and upgrade.
What is the essential characteristic of colloid that distinguishes it from other dispersoids?
Analysis: It is the diameter of dispersoid particles, and the Dindar effect of colloid is related to this feature.
Step 4: Summarize the homework.
Ask the students to answer what they have gained in this class, what they have learned and how they feel about learning.
Homework: What are the other properties of colloid? Preview after class.
Special analysis of national defense
1. Are all metal oxides basic oxides?
Reference answer
No, Na2O2 is a metal oxide, but it is not a basic oxide.
2. Talk about the role of experiment in teaching.
Reference answer
Experiments help to stimulate students' interest in learning chemistry, create lively teaching situations, help students understand and master chemical knowledge and skills, enlighten students' scientific thinking, train students' scientific methods and cultivate students' scientific attitudes and values.
Version 2
First, review the test questions
High school chemistry "extraction"
Try to talk about this topic.
1. Subject: Extracting
2. Contents:
Using the different solubility of substances in immiscible solvents, one solvent is used to extract substances from the solution composed of it and another solvent. This method is called extraction. The operation of separating two immiscible liquids after extraction is called liquid separation. Separating funnel is often used for liquid separation.
(1) Measure 10mL of saturated aqueous solution of iodine with a measuring cylinder, pour it into a separatory funnel, then inject 4mL of carbon tetrachloride, and cover it with a glass stopper.
(2) Hold the mouth of the separatory funnel with the right hand, hold the piston part with the left hand, invert the separatory funnel and oscillate it to make the two liquids fully contact (as shown in Figure1-7); After shaking, open the piston to release the gas in the funnel.
(3) Put the separating funnel on the iron frame and let it stand (as shown in figure 1-8).
(4) After the liquid is stratified, open the glass stopper on the neck of the separatory funnel, or align the groove (or small hole) on the stopper with the small hole on the funnel, and then unscrew the piston below the separatory funnel to make the lower liquid slowly flow down the beaker wall (as shown in figure 1-9).
Figure 1-7 Close the glass stopper and piston when reversing the separating funnel Figure 1-8 Extraction Figure 1-9 Separation.
3. Basic requirements:
(1) There should be appropriate questions in the teaching process, and attention should be paid to the interaction between teachers and students.
(2) The teaching process requires experiments or simulated demonstrations with relevant teaching AIDS.
(3) The blackboard design should match the teaching content.
Defense topic
What is the principle of 1. extraction?
2. What should a teacher guide students when conducting independent extraction experiments?
Second, the analysis of test questions
teaching process
Link 1: physical import
Physical display shows spherical and pear-shaped separatory funnels.
We often use a spherical separatory funnel in junior high school, which is also called a separatory funnel. What's the difference between it and a spherical separatory funnel?
Students answer that the neck is short and the bucket is big.
The teacher guided this funnel to be called pear-shaped separatory funnel, and we will use it to do an experiment today.
Link 2: Explore new knowledge
The teacher instructed that the pear-shaped separatory funnel should be leak-checked before participating in the experiment to determine whether it can be used.
Leak detection and operation of pear-shaped separatory funnel in demonstration experiment.
(Close the cock at the neck of the separatory funnel, inject a proper amount of distilled water into the separatory funnel, and observe whether there is any leakage at both ends of the cock and the lower mouth of the funnel. If not, close the upper grinding plug, hold the cock with your left hand, press the upper grinding plug with your right index finger, and stand upside down to check whether there is air leakage; If there is no water leakage, stand upright, rotate the upper grinding plug by 180 degrees, and stand upside down to check whether there is water leakage. If there is no water leakage, a separatory funnel can be used. )
Leak detection operation of pear-shaped separatory funnel in students' experiment.
The teacher guided a pear-shaped separating funnel to do a new liquid-liquid separation experiment to separate iodine from iodine water.
Ask questions and think about the principle of extraction.
Students answer that the solubility of substances in immiscible solvents is different, and use one solvent to extract substances from the solution composed of it and another solvent.
Why choose carbon tetrachloride as extractant to extract iodine from iodine water?
Because iodine is soluble in carbon tetrachloride, but carbon tetrachloride is insoluble in water and does not react, it can be used as an extractant.
Ask questions and summarize the operation steps of the extraction experiment with the demonstration experiment in the video.
Students answer (1) Measure 10mL of saturated aqueous solution of iodine with a measuring cylinder, pour it into a separating funnel, then inject 4mL of carbon tetrachloride and cover it with a glass stopper.
(2) Hold down the opening of the separating funnel with the right hand, hold the piston part with the left hand, and invert the separating funnel to oscillate, so that the two liquids can fully contact; After shaking, open the piston to release the gas in the funnel.
(3) Put the separating funnel on the iron frame and let it stand.
Question: How does the color of the separating funnel change before and after extraction? What do the upper and lower solutions contain after extraction?
The students answered that before the extraction, the iodine water in the funnel was yellow-brown, and after the extraction, the liquid was divided into two layers, the upper layer became shallow and the lower layer was purple-red, which was a carbon tetrachloride solution of iodine.
Ask questions and think about how to separate the upper and lower layers of the solution after extraction. What is the reason?
Students answer that the lower solution flows out from the lower mouth and the upper liquid pours out from the upper mouth; The purpose is to make the target product more pure. You can make mistakes and the teacher will correct them. )
Demonstrate the liquid separation experiment.
After the liquid is stratified, open the glass stopper at the neck of the separating funnel, or align the groove (or small hole) on the glass stopper with the small hole on the funnel, and then unscrew the piston below the separating funnel, so that the lower liquid can slowly flow down the beaker wall. The upper liquid should be poured out from the upper mouth of the separatory funnel.
The teacher summed up, filling liquid → shaking well → standing → separating liquid.
Link 3: Expansion and Promotion
Students experiment to extract iodine from iodine water, and teachers patrol and guide.
Step 4: Summarize the homework.
Summary: Teachers and students * * * summarize the content of this lesson.
Homework: Students are required to summarize the methods and scope of application of substance separation and purification after class.
Special analysis of national defense
What is the principle of 1. extraction?
Reference answer
Extraction is a unit operation, which uses the different solubility of each component in the system in the solvent to separate the mixture. That is, the method of transferring solute substances from one solvent to another by using the solubility difference of substances in two insoluble (or slightly soluble) solvents.
2. What should a teacher guide students when conducting independent extraction experiments?
Reference answer
In the process of students' independent experimental operation, teachers patrol to guide and help solve potential safety hazards, irregular operation, instrument problems (such as pear-shaped funnel leakage) in the experimental process, and also guide students to observe and record experimental phenomena in the experimental process.
Version 3
First, review the test questions
High School Chemistry "Nitrogen Cycle in Nature"
Try to talk about this topic.
1. Subject: Nitrogen Cycle in Nature
2. Contents:
Nitrogen is an important component of animals, plants and protozoa (such as fungi and bacteria), and it is also an essential element to maintain the activities of higher animals and plants, so the cycle of nitrogen involves all aspects of the earth's biosphere.
In nature, rhizobia in the roots of leguminous plants such as soybeans and broad beans transform nitrogen in the air into nitrogen-containing compounds such as nitrates. Ammonium ion (NH4+) and nitrate absorbed by plant roots from soil undergo complex biotransformation to form various amino acids, which are finally transformed into protein. Animals get plant protein from plants and convert it into animal protein. Protein in animal and plant residues is decomposed into NH4+, NO3- and NH3 by microorganisms, and then returns to soil and water, and is absorbed and utilized by plants again. In addition, under the discharge condition, a small amount of nitrogen in the air combines with oxygen to generate nitrogen oxides, which enter the soil and water body with water.
Another aspect that affects the nitrogen cycle in nature is human activities. People convert nitrogen in the air into ammonia by chemical methods, and then convert ammonia into various nitrogen-containing compounds (such as nitrogen fertilizer and nitric acid) according to needs. Some nitrogen-containing compounds are converted into soil, atmosphere and water. Nitrogen oxides produced by the burning of fossil fuels and the burning of forest and crop branches and leaves enter the land and ocean through the atmosphere and participate in the nitrogen cycle.
3. Basic requirements:
(1) needs a simple blackboard design to match the teaching content.
(2) There should be classroom interaction in the teaching process.
(3) Please complete the trial lecture in ten minutes.
Defense topic
1. What are the important substances in the nitrogen cycle?
2. What teaching methods have you adopted in this course?
Second, the analysis of test questions
teaching process
Link 1: Introduction
Play the video The teacher played a video of lightning before class.
It is a natural phenomenon for teachers to guide lightning. As the saying goes, "a thunderstorm brings a fertilizer." After the thunderstorm, people found that the crops were growing well and the leaves were green, just like nitrogen fertilizer had just been applied. So what fertilizer does the thunderstorm produce? How did it come about? This lesson is the same as learning the nitrogen cycle.
Link 2: New Curriculum Teaching
The reading guide guides students to read the materials in the textbook about "nitrogen cycle involves all aspects of the earth's biosphere"
Please carefully observe the textbook Figure 3-2-2 to ask questions and tell me how nitrogen circulates in nature.
Students' answers presuppose that students analyze animals and plants, thunderstorms and human activities.
The teacher asked three ways of nitrogen cycle. Please find out several nitrogen-containing substances in the process of nitrogen cycle, write their chemical formulas, mark the valence of nitrogen and point out their substance categories.
Students answer to find nitrogen-containing substances in combination with nitrogen cycle, write down the chemical formula, standardize the valence, point out the category, and then report to the group representatives.
The teacher guides and perfects the imperfections.
The teacher asked: What effect will human activities have on the nitrogen cycle in nature?
Students answer that people convert nitrogen in the air into ammonia by chemical methods, and then convert ammonia into various nitrogen-containing compounds (such as nitrogen fertilizer and nitric acid) according to needs. Some nitrogen-containing compounds are converted into soil, atmosphere and water. Nitrogen oxides produced by the burning of fossil fuels and the burning of forest and crop branches and leaves enter the land and ocean through the atmosphere and participate in the nitrogen cycle.
Link 3: Consolidate and improve
The teacher asked to show the nitrogen cycle in the biosphere in a graphic way.
group discussion
Special analysis of national defense
1. What are the important substances in the nitrogen cycle?
Reference answer
The important substances in the nitrogen cycle are mainly nitrogen, nitric oxide, nitrogen dioxide, ammonia and nitric acid.
2. What teaching methods have you adopted in this course?
Reference answer
The teaching methods I use in this course are dialogue, discussion and reading guidance. First of all, conversational approach runs through the whole teaching process. In teaching, I put forward some guiding questions, such as "what are the ways of nitrogen circulation in nature, and what effects will human activities have on nitrogen circulation in nature?" And so on, guide students to learn. Secondly, because the content of this course is relatively simple, students are allowed to read the relevant contents in the textbook independently and draw the flow chart of nitrogen cycle in the biosphere in groups, which stimulates students' initiative and enthusiasm in learning.