How to turn waste into treasure in chemical experiments.
[Abstract] This paper introduces how to recycle and treat the products and wastes in chemical experiments from five aspects, such as using the leftovers of chemical experiments as raw materials for other experiments, and making full use of the waste liquid in waste acid tank and waste alkali tank, so as to turn waste into treasure.
[Keywords:] chemical experiment waste environment
Most of the wastes from chemical experiments are flammable, corrosive, reactive, toxic, and some even cause cancer. If it is directly discharged into the environment without any treatment, it will undoubtedly pollute and endanger the surrounding environment and harm human health. In the traditional chemical experiment, students observe the relevant phenomena and data, and after achieving the experimental purpose, dump or discharge the products directly. We follow the concept of green chemistry and recycle the products and wastes of each experiment, which not only saves drugs, but also reduces or avoids the pollution caused by harmful substances entering the environment.
First, keep the product in the preliminary experiment.
If ammonium ferrous sulfate, the experimental product in the preparation of ammonium ferrous sulfate, is directly discarded after the experiment, it will not only pollute the environment, but also not conform to the concept of building a resource-saving and environment-friendly society. In practical teaching, we recovered ammonium ferrous sulfate obtained in the experiment and used it as the synthetic raw material of iron oxalate in subsequent experiments, making the experiment green.
The refined salt after the purification of the original salt and the zinc particles used in the dissociation equilibrium are all reserved for the subsequent experiments.
Second, the leftovers from chemical experiments are used as raw materials for other experiments.
CuSO4 in the experiment? Anhydrous copper sulfate powder obtained by measuring the crystal water content in 5H2O crystal can be used to test whether there is water in alcohol. A large number of 0. 1mol/LCuSO4 and ZnSO4 solutions used in electrochemical experiments were used in subsequent qualitative experiments of sulfide precipitation solubility. The toxic gas in the experiment is regarded as an intermediate product, and some by-products can be obtained by increasing the absorption or treatment device of toxic gas. For example, Na2SO3 can be obtained by treating SO2 with NaOH solution.
As long as teachers and students pay attention and carefully design and study continuous experiments, there are still many places that can be recycled. In the process of recycling and harmless treatment, students' awareness of environmental protection can be strengthened, and students' good experimental habits and practical operation ability as well as their ability to explore, discover and solve problems can be cultivated.
Thirdly, the recovery of waste liquid containing Ag+
Na2S solution was added to the silver-containing waste liquid to completely convert Ag+ into Ag2S precipitate. After washing the black Ag2S precipitate with deionized water, dry the precipitate with small fire, then add NaNO3 solid, burn it on a blowtorch until no NO2 brown gas is generated, and clean the residue after cooling. After drying again, Na2CO3 and Na2B4O7 are added? 10H2O (sodium tetraborate) solid mixture (mass ratio: 1 1), evenly stirred, put into a porcelain crucible, and heated in a muffle furnace at 950℃ ~ 1000℃ for 20 minutes. After taking out the crucible, carefully pour out the upper slag while it is hot, and the lower slag is metallic silver.
Silver is an expensive rare metal. In recent years, the price of silver salt has been rising, which greatly increases the cost of analysis and determination of silver salt. Therefore, it is of great significance to recover silver from silver-containing waste liquid and regularly treat or prepare commonly used reagent silver nitrate.
4. Recovery of waste liquid containing Pb2+ and Bi3+
Na2S is used as precipitant to treat the waste liquid. The recovered waste liquid is heated to near boiling, and Na2S solution is added with stirring to transform it into insoluble black precipitate of PbS and Bi2S3. Filter and wash the precipitate, then add concentrated nitric acid and heat until the black sulfide is dissolved.
The reaction can be carried out in a conical flask. The mouth of the conical bottle is equipped with a double-hole rubber stopper. One hole is inserted into the separating funnel for adding nitric acid, and the other hole is inserted into the glass air duct. The airway is inserted into a small beaker filled with dilute NaOH solution, so that NO2 gas generated by the reaction is absorbed by the solution, and toxic gas is prevented from polluting the environment. By controlling the amount of nitric acid, the regenerated test solution can be used repeatedly by students in the experiment.
Verb (abbreviation for verb) turns solid waste into treasure.
Chemical laboratory will produce a large number of damaged test tubes every semester, which can be reprocessed. If the bottom and mouth of the test tube are damaged, glass cutter or triangular file can be used to cut off the damaged part to make a bidirectional reaction tube or a short test tube. The broken glass conduit can be made into a rubber-tipped dropper; The combination of a test tube with a hole in the bottom and a beaker can be used as a simple pickled fish generator. The used filter paper of the glass electrode was wiped with an acid meter, used to absorb kerosene in the experiment of sodium and potassium, and used to dry the crystal when preparing copper sulfate crystal.
Six, make full use of waste liquid in waste acid tank and waste alkali tank.
Collecting waste acid and waste alkali in the experiment not only reduces the corrosion of sewer, but also realizes the utilization of waste.
Part of the waste acid can be used in some subsequent experiments, or collected as laboratory lotion, which can appropriately replace the chromium pickling solution harmful to human body; It is also effective for washing potassium permanganate residue, old lime bottle and removing rust spots. After the inferior drugs are diluted, we use them to wash sinks, toilets and so on.
Waste alkali is put in the medicine box of volatile acid to eliminate acid gas. When the winter and summer vacations came, a few pots of waste lye were put in the pharmacy, which greatly eliminated the sour smell and bromine gas.
Some waste liquids with no recycling value are usually non-acidic, that is, alkaline, and cannot be directly discharged, otherwise the pH value in water will be lowered or increased. When the concentration of inorganic acid, alkali and salt waste liquid is low, it should be washed with a lot of water and diluted to below 65438 0% before it can be directly discharged from the sewer.
Seven, the recycling of other waste materials
There is a lot of waste in the laboratory that can be recycled. For example, the cut waste printer can be used as the weighing paper of the student tray balance, and the parts of the waste instrument can be removed for the maintenance of other instruments. Waste electric furnace wire can be sanded and melted at one end of the glass tube, which can be used as a substitute for nickel-chromium wire in the flame reaction experiment, and the effect is also very good.
It should be pointed out that some experimental wastes can be recycled, some are only suitable for treatment, and some are both, so we should treat them differently, and not everything can be recycled. For example, the most prominent problem of manganese dioxide extracted from the influence of catalyst on chemical reaction rate is that it is too dirty and stains are difficult to wash. Wherever these waste residues meet, there will be trouble, which is really not worth the candle. The best way to handle it is to collect it and bury it.
The deteriorating environment is a serious threat to human survival and economic development, and people are increasingly aware of the importance of protecting the environment. In the recycling of experimental products and wastes, teachers and students have experienced the pleasure of turning waste into treasure, and its significance is reflected in teaching, environmental protection, economy and many other aspects:
1. Cultivate students' sense of responsibility and good ideology and morality, inspire students to establish the concepts of waste utilization, energy saving and making the best use of everything in their future work, and consciously enhance their awareness of environmental protection and health care.
2. The recovery of experimental drugs needs a process of learning, using and solving practical problems. This vivid teaching can stimulate students' interest in learning, which is of great significance to cultivate students' scientific attitude, ability to analyze and solve problems and ability to practice experiments.
3. It reduces the corrosion of public facilities (such as sewers) and avoids causing great pollution to the environment, which has environmental protection significance.
4. save money. The money saved by recycling a drug is meager, but every year, three professional 10 teaching classes insist on doing all 60 hours of experiments, and the money saved can reach tens of thousands of yuan, which can reach millions in the long run and macroscopically.
In the group experiment, teachers should infiltrate environmental protection knowledge, enhance students' awareness of environmental protection, and arrange students to recycle waste in a planned way. Encourage students to use and dispose of waste. Only when people generally establish environmental awareness can they form a social force to protect the living environment of human beings.
References:
[1] Zhang Qingyun. Comprehensive utilization of chemical experimental products in middle schools [J]. Chemistry Education, 2000, (5).
[2] Li Jun. Thinking of Green Chemistry Laboratory [J]. Chemistry Education, 2002, (1).
[3] Deng Yuhong. Green chemistry course-a new concept of chemistry education [J]. Middle school chemistry teaching reference, 2002, (1-2).
Zhou Gaiying, Lin Xixun. Improving experiments, reducing pollution and promoting green chemistry education [J]. Experimental Teaching and Instruments, 2003, (6).
Turn waste into treasure. The second part uses mistakes to turn "waste" into "treasure"
In many years of junior high school mathematics teaching practice, I found that the mistakes made by each student are very similar, and each mistake will be repeated many times. The main reason is that students don't pay attention to their mistakes and lack sorting. Students' mistakes mainly come from test papers and exercise books, so in order to make students pay attention to mistakes, I adopted the method of re-approving when correcting homework. In the revision of the test paper, the detailed process of making mistakes should be written in the multiple-choice questions and fill-in-the-blank questions on the test paper; In order to find out the typical mistakes in my homework, I often list them in class; In order for teachers and students to sort out the wrong questions, teachers and students prepare the wrong questions together after class.
Keywords: attention; Use; mistake
China Library ClassificationNo.: G633.6 Document IdentificationNo.: B DocumentNo.:1672-1578 (2013) 03-0168-01.
Contemporary scientist Popper said: "Mistakes often breed more factors of discovery and creation than correctness." Therefore, it is very important to reflect on mistakes, find out where mistakes are easy to make, recall the results and process of solving problems, find out the root causes of mistakes, analyze the causes of mistakes, put forward improvement measures, and clarify the correct ideas and methods to solve problems.
1. Let students pay attention to the mistakes.
For students' mistakes, if teachers repeat their explanations with wishful thinking and correct them directly, without students' active participation, the effect is often poor. Students' mistakes mainly come from exercise books and test papers. Paying attention to mistakes means paying attention to mistakes in exercise books and test papers.
At present, middle school math homework is mainly doing exercises. The main purpose of teachers' correction is to supervise and check and understand students' mastery of knowledge. When correcting, judge right or wrong and grade them. In the past, I found that students only wrote their homework to cope with the teacher and to complete their homework. Most students ignore the homework corrected by the teacher. Only a few students will try to understand the wrong questions and think about why they are wrong. They really won't ask the teacher. It is observed that this tiny part is often students with excellent grades. It is precisely because they have developed good study habits that they realize that they have not corrected the wrong questions or grasped the learning opportunities. In order to make more students notice the mistakes, I began to take the method of re-approving when correcting the homework, that is, I would browse the revised homework again, first to see if the students have revised it, and then to see if the students have revised it correctly. If all the corrections are correct, I will enter A+ to make corrections. If any question is wrong, I will indicate which question is still wrong and needs to be corrected. This is to let students pay attention to mistakes, and don't turn a blind eye to people who do wrong questions. For those students who don't correct their homework in time or don't correct it correctly, I will often use the break time to personally send the exercise books to the students and give them suggestions on how to correct their homework.
When I first started working, the method I chose to analyze the test paper was to talk about every question on the test paper. Later, I found that I spoke with relish. The students with excellent grades listened carefully below, and the students with poor grades listened drowsily below. If you encounter similar problems in the future, the mistakes will be repeated. Facts have proved that such a test paper analysis method is not feasible. Later, I changed a test paper analysis method. I don't analyze the test paper immediately after every exam. For the wrong questions, I ask students to state the reasons for the mistakes. This is to let the students notice the mistakes themselves and correct them first. At the beginning, I found that many students didn't see the wrong questions clearly or didn't understand them, so that some students didn't really correct them. Finally, I ask students to really correct the wrong questions, that is, write the detailed process of the wrong questions in the multiple-choice questions and fill-in-the-blank questions of the test paper.
"Learn from mistakes", and the lessons learned from mistakes are even more thought-provoking. Students often have some wrong thinking methods in solving problems. Only when students attach importance to their mistakes, face up to them, actively think, review, test, tell and question, will their understanding of mistakes be clearer and deeper. We will reflect on correcting mistakes and find out the wrong way of thinking, so as to better find out mistakes and gain new knowledge. Therefore, when analyzing mistakes, teachers should not just tell students that it is wrong to do so, but how to do it correctly. Instead, we should give students time and space to think independently, and pay more attention to guiding students to think about why this is wrong, that is, let students know why this is wrong. In the process of thinking, students will realize that learning mathematics can't rely on mechanical memory, and they should find the root cause, which also cultivates students' research ability invisibly. What students get in the face of mistakes is not nervousness and shame, but rational analysis and reflection.
2. Take advantage of students' mistakes
In mathematics teaching, teachers should start from students' mistakes, regard students' mistakes as valuable teaching resources, take advantage of the situation, protect students' enthusiasm for learning, stimulate students' awareness of learning, and make the classroom a stage for students to realize their own active development. Students' mistakes are the real exposure of students' thinking and the first feedback after learning knowledge, which hides rich teaching resources and is of great research value. Immediately make a scientific and reasonable analysis and accurate judgment on the causes of the errors in students' homework: whether this error is a habitual error, a cognitive interference error or a conceptual error; Whether this mistake is typical, whether it is * * * or an individual problem; Whether it is necessary to focus on discrimination and so on. Only by knowing students' mistakes can teachers prescribe the right medicine and choose effective teaching strategies and methods flexibly and pertinently. When mistakes occur, teachers should take mistakes as counterexamples, so that students can discover the essential characteristics of the problem and make their knowledge more accurate. For example, in the process of mixed operation of rational numbers, many students always confuse -22 and (-2)2 and think that the results are all 4, which is a * * * problem. The cause of the error is a conceptual error. For -22 and (-2)2, it is considered as the square of -2, so the results are all 4. Here, the teacher needs to emphasize the difference between the two. -22 represents the reciprocal of the square of 2, and -2 is the square of -2. The reason for the error is that students forget that when the radix is negative, the radix must be enclosed in brackets. For example, when teaching exercises, teachers should insert students' mistakes, project students' original answers, let students evaluate the problem-solving process and find out the irregularities or mistakes in solving problems. When solving the unary linear equation 1-4-3x4=5x+36-x, students mainly make the following typical mistakes after removing the denominator.
( 1) 1-3(4-3x)= 2(5x+3)-x
(2) 12- 12-9x = 10x+6- 12x
(3) 1- 12-9x = 10x+6-x
(4)3-3(4-3x)=(5x+3)-2x
(5) 1- 12-3x = 10x+3-x
I filmed these mistakes and projected them on the screen. Let's correct it together. Finally, we come to the conclusion that the first mistake is because the multiplication without denominator was omitted when naming. The second mistake is because the numerator is a polynomial without brackets after removing the denominator; The third one has two mistakes. One is to omit the item without denominator when removing the denominator, and the other is that after removing the denominator, the numerator is multiple.
Type, without parentheses; The fourth mistake is to make an appointment too early, such as12 (1-4-3x4) =12 (5x+36-x). Do you want to remove the brackets from 12- 12 first? 4-3x4 12？ 5x+36 12x, and then about12-3 (4-3x) = 2 (5x+3)-12x; There are two mistakes in the fifth formula: one is to omit the item without denominator when removing denominator, and the other is to omit the following item when removing brackets. Through the above analysis, we can draw the conclusion that (1) should be paid attention to when naming, and items without denominator cannot be omitted; (2) After removing the denominator, the numerator is a polynomial, and brackets should be added; (3) When deleting brackets, each item in brackets should be multiplied by the previous number.
Bruner once said: "Students' mistakes are valuable and the wealth of teaching. In the process of constantly correcting mistakes, students will gain new knowledge, improve their ability and enhance their experience. "As a teacher, we should regard these mistakes as signposts for students to improve on their learning path, look at the mistakes in students' learning from the perspective of resources, make good use of the mistakes of students, and strive to turn waste into treasure, so that the teaching sky will be broader.
3. Teachers and students * * * have sorting errors.
Finally, let the students prepare the wrong question book and collect and sort out the wrong questions. Everyone will make some mistakes when doing math exercises. It is a good way to cultivate students' reflective ability to record these mistakes in a special book and establish their own mathematical error question bank, so that students can get the information of the reflective object and make up for the lack of knowledge and thinking in reflection. In this math mistake question bank, students should record the wrong questions in time, carefully analyze the causes of the mistakes, and put forward improvement measures in order to learn lessons and prevent such situations from happening again. For the wrong book, some students copied the wrong questions, and some students cut the wrong questions on the test paper and pasted them in the book, and wrote the correct answers through reflection.
As a teacher, you should also prepare a notebook to record students' typical mistakes. For example, I write down the typical mistakes of the above linear equation, and I also write down which students are prone to make mistakes in my notebook, so as to pay more attention to these students in class, and I can also use my spare time to tutor them. In addition, according to the characteristics of teaching content and related knowledge, teachers can use the accumulated experience in the past to predict mistakes, accurately grasp error-prone points, and integrate error-prone and confusing knowledge points into classroom teaching, so that students will have a certain impression at the first contact, and make preparations in advance to nip in the bud.
Psychologist Gayer said: "Whoever doesn't consider trial and error and who doesn't allow students to make mistakes will miss the most productive learning moment." Students will make many unexpected mistakes in practice for various reasons. For these mistakes, if we can further analyze the causes of students' mistakes, find out related problems through mistakes, and do some articles on them, we can turn "waste" into "treasure" and use mistakes as resources to serve teaching.