Experimental reagents: dilute nitric acid, silver nitrate, saturated saline, sodium hydroxide solution, starch potassium iodide paper, phenolphthalein, iron rods, graphite rods, etc.
Natural seawater, the main elements of the composition
Chinese name chemical symbol content
(mg / l) Chinese name chemical Symbol Content
(micrograms/liter)
Chlorine Cl 18880 Carbon C 28
Sodium Na 10770 Nitrogen N 15
Magnesium Mg 1290 Strontium Sr 7.9
Sulfur S 884 Boron B 4.5
Calcium Ca 412.1 Silicon Si 2
Potassium K 399 Fluorine F 1.3
Bromine Br 67.3
Bromine Br 67.3
Teacher: Show a bottle of seawater, seawater taste bitter and salty, which is related to the composition of seawater, so how do we test the presence of chlorine ions in seawater?
生：向海水中滴加用稀HNO3酸化的AgNO3溶液，如果出现白色沉淀淀，证明有氯离子。
[Demonstration] Add AgNO3 solution acidified with dilute HNO3 into the test tube with appropriate amount of seawater.
Teacher: the oceans account for seventy-one percent of the total area of the earth
[projection] textbook Figure 2-1 per kilogram of seawater in the content of several kinds of chlorides
students: understand that seawater is rich, seawater contains a fairly high content of chlorides, mainly sodium chloride, followed by magnesium chloride, calcium chloride and potassium chloride.
Teacher: seawater is rich in sodium chloride, so how do people get sodium chloride from seawater and use sodium chloride?
[Play video] The process of salt production in seawater
Teacher-student interaction: the application of sodium chloride
Life: life-sustaining elements
Medical: saline
Industry: the production of soda ash, caustic soda, chlorine, etc.
[Transition] Chlorine in nature is in the form of ions, not in the form of the free state, so how was Cl2 discovered? So how was Cl2 discovered?
Students: read the textbook P40 History of Chemistry and carefully observe the schematic diagram of the experimental setup of the laboratory production of chlorine gas
Teacher: guide the students to observe the experiment, think and summarize the principles of the laboratory production of chlorine gas, the collection of chlorine gas, and the absorption of exhaust gas.
[Group discussion] 1, the method of collecting chlorine?
2, how to know that the chlorine gas has been collected?
3. What is the role of sodium hydroxide solution?
[Summarize and add] 1, the collection of chlorine gas can be used in addition to the upward exhaust method, can also be used to exhaust saturated saline method of collection.
2, test whether the gas is collected full in addition to observing the color, you can also use a moist starch KI test paper on the mouth of the bottle to test (the paper turns blue).
3, with NaOH solution to absorb the exhaust gas Cl2. NaOH + Cl2 === NaCl + NaClO + H2O
[Transition] Since seawater is rich in chlorine, can we use seawater to produce chlorine?
[Activity and Investigation]If you add sodium chloride to water, what substances may be obtained on the two electrodes after energizing? The device is shown in the figure:
Step 1: Turn on the power supply, observe the changes in the U-shaped tube
Phenomenon: cathode, anode near the bubbles are produced
Conclusion: there are new gases produced by the energized
Student: boldly speculate on the two electrodes of the gas produced may be what?
Step 2: turn off the power, open the rubber plug at the anode end of the U-shaped tube, quickly use tweezers to put the wet starch potassium iodide test paper on the mouth of the test tube, observe the phenomenon
Phenomenon: the wet starch potassium iodide test paper turns blue
Conclusion: the gas produced by the anode is chlorine gas
Step 3: the use of syringe to draw out the cathode of the gas produced, and quickly press the Move the syringe closer to the lit alcohol lamp, release your thumb and push out the gas from the syringe.
Phenomenon: the gas can be burned, and accompanied by a slight popping sound
Conclusion: the gas produced by the cathode is hydrogen
Step 4: open the rubber plugs at both ends of the U-tube, respectively, add 1-2 drops of phenolphthalein solution to the solution, observe the phenomenon
Phenomenon: the color of the solution near the cathode becomes red
Conclusion: there are alkaline substances in solution
The gas produced by the cathode is hydrogen. Generation
Sheng: According to the conclusion of the experiment to write the chemical reaction equation
2NaCl + 2H2O H2↑ + Cl2↑ + 2NaOH
[Summary] industry is the use of this principle, the electrolysis of saturated saline method of chlorine, in the electrode connected to the positive electrode of the power supply (anode) collection of chlorine, and the power supply is connected to the electrode of the negative electrode to produce Hydrogen gas is produced at the electrode connected to the negative electrode of the power supply, and sodium hydroxide is produced in the solution.
A student asked the question, "Teacher, why don't you extract both Cl2 and Na at once, so that you don't get two birds with one stone?"
The teacher replied: "This student raised a very good question, in the second unit of our study of sodium metal extraction is the use of electrolysis of molten sodium chloride to produce sodium metal, and at the same time get chlorine gas. However, because of the low concentration of sodium chloride in seawater, but also with the equipment requirements, profit is also related, so in the industry to use this principle. Of course, there are some drawbacks if the whole device is used in industry? Think about it, what are the disadvantages?"
Students: H2 and Cl2 mixing will cause an explosion
Teacher: guide the students from the chlorine tail gas absorption principle as a starting point for consideration, it is easy to conclude that the generated NaOH and Cl2 will react.
Therefore, in order to get sodium hydroxide and chlorine, we must try to separate the generated sodium hydroxide and chlorine, and not let them come into contact.
[Expanded] Ion Exchange Membrane Electrolysis of Salt Water
Summarize: The cation exchange membrane is very selective, it only allows cations to pass through, and prevents anions and molecules from passing through, which allows only Na+ and H+ to pass through, while Cl-, OH- and gases cannot pass through.
Division: "Chlor-alkali industry" concept
[Knowledge application] According to the chlor-alkali plant raw materials and the nature of the product, you think in the production process and storage and transportation should pay attention to what problems? Chlor-alkali plant site should be how to choose?
Chlorine gas is stored in cylinders, keep cool and ventilated. NaOH solid should avoid contact with air to prevent deliquescence. Chlor-alkali plant site selection, students only considered the chlorine gas is toxic, should be in the suburbs, in the direction of the prevailing winds downwind of the place, the teacher suggests that generally from raw materials, water, energy, land supply, market needs, transportation, environmental protection and other considerations, as extracurricular homework, so that the students go back to check the information to solve.
Nine, board design
Unit 1 Chlorine, bromine, iodine and their compounds
I. Chlorine production principles
(a) laboratory method
1, the experimental principle: 4HCl (concentrated) + MnO2 === MnCl2 + 2H2O + Cl2↑
2, the collection device: upward exhaust method or saturated saline method
2, the collection device: upward exhaust method. Exhaust saturated saline method
3, the method of fullness: look at the color or use wet starch potassium iodide test paper
4, tail gas treatment: sodium hydroxide solution
2NaOH + Cl2 = NaCl + NaClO + H2O
(B) industrial method
1, electrolysis of saturated saline water: 2NaCl + 2H2O H2 ↑ + Cl2↑ + 2NaOH
2, the role of cation exchange membrane
3, the concept of chlor-alkali industry
X. Case evaluation
The design of this case has the following characteristics:
1, the natural resources of seawater as the object of the study, leading to the extraction of more total reserves of chemicals (sodium chloride), and as a carrier to explore the typical non-natural resources. As a carrier to explore the production principle of typical non-metallic monomers chlorine, revealing the basic principles and nature of chemical reactions. This will enable students to acquire the relevant chemical knowledge and experimental research skills, and at the same time, form the understanding that the use of natural resources requires the development of chemical science, and stimulate the interest in learning chemistry for self-development and social production progress.
2, emphasizing the important role of chemical experiments in the learning of chemical knowledge, through the observation and analysis of experimental phenomena, so that students to summarize their own, is a feature of this section of the teaching. Chlorine laboratory method, is the beginning of the students to learn the laboratory gas, taking into account the teaching time and the organization and management of the experiment, in this lesson, as long as the connection of the experimental equipment, exhaust treatment and precautions can be clear, the experimental skills and the principle of not expanding.
3, "chlor-alkali plant site selection" of this issue, so that the classroom knowledge and social production of practical combination, stimulate students' curiosity. So that students to establish environmental awareness, start from me, give full play to the imagination of students, so that the education. Timely feedback knowledge, deepen the understanding of the experimental knowledge of electrolysis and application.
4, for experimental teaching conditions for good schools, electrolysis of saturated saline water experiment can be changed to group experiments, you can let the students through hands-on access to vivid and intuitive first-hand information, so that the students in the scenario of easy and pleasant to find the problem.
References