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Junior high school chemistry students who are required to participate in the teacher recruitment examination interview (simulation lecture)
First, the teaching objectives
Knowledge and skills
Understand the definition of solubility; Draw the solubility curve and make a preliminary analysis.
Process and method
By drawing the solubility curve, we can experience the process of data processing and learn the methods of data processing.
Emotional attitudes and values
Through the definition of solubility and the drawing of solubility curve, we can develop a rigorous scientific attitude.
Second, the difficulties in teaching
The meaning of solubility of key solid substances.
It is difficult to obtain relevant information using solubility curve.
Third, the teaching process
Link 1: Introducing a new lesson
In the previous experiments, we already know that there is the largest mass of soluble sodium chloride or potassium nitrate in 20 ml of water. What is the maximum mass?
The student's answer is the mass that can be dissolved when forming its saturated solution.
The teacher guided this to show that the amount of solute dissolved in a certain amount of solvent is limited at a certain temperature. So in chemistry, how to express this limit quantitatively? We have introduced the concept of "solubility". Today, let's learn about solubility.
Link 2: New Curriculum Teaching
1. solubility
Ask questions, read textbooks and answer what is solubility, and how to express the solubility of solid matter?
Students answer the mass of solid matter when it reaches saturation in 100g solvent.
When asking questions to describe solubility, temperature, solvent amount and saturation state are all limited. Why? What is the unit of solubility?
Students answer that the amount of substances dissolved in a certain amount of solvent will change with the change of temperature; The amount of solute that can be dissolved varies with the amount of solvent. The definition of solubility is to specify the maximum value that solute can dissolve in 100g solvent, thus defining the saturated state. The unit of solubility is grams.
At 20℃, 100g water can dissolve 36g sodium chloride at most (when the solution reaches saturation state), so what is the solubility of sodium chloride in water at this temperature?
The student replied that the solubility of sodium chloride in water is 36g at 20℃.
2. Draw solubility curve
Student activities According to the table "Solubility of several substances at different temperatures", try to draw the solubility curves of NaCl, KCl and five substances.
(Give students 15 minutes to draw the curve)
The question is whether the solubility of five substances at 25℃ and 85℃ can be calculated according to the curve. What conclusion have you reached?
The student answered yes. It shows that the solubility value of a substance at a certain temperature can be obtained from the solubility curve.
According to the solubility curve drawn, what is the law of solubility of these substances changing with temperature? Give examples.
Students answer that the solubility of these substances increases with the increase of temperature; The solubility of NaCl does not change much with the increase of temperature. Solubility decreases with the increase of temperature.
What other information can be obtained from the solubility curve?
Ask questions and continue to observe the solubility curve. Are the solubility of several substances the same at 100℃? What does this mean?
Students' answers are different. The maximum solubility of is 77.3g, while the solubility of is only 0.07g, which shows that the solubility of several substances is different at the same temperature.
What does the intersection of two solubility curves represent?
The student's answer means that the solubility of the two substances is the same at this temperature.
Link 3: Expand and upgrade.
Both solubility data table and solubility curve can indicate the solubility of substances at different temperatures. What's the difference between them?
Analysis:
Solubility data table has the advantages of accurate data and reliable source; Solubility curve can display more complete data, and can directly see the change law of solubility and temperature.
Step 4: Summarize the homework.
Ask the students to answer this lesson: solubility.
Homework: preview the gas solubility section.
Fourth, blackboard design.
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