学习《必修1》第一章的“萃取”时，“萃取”知识在课本中只有三行半和一个四氯化碳萃取碘的实验，而“萃取”是高考的一个考点，如何让学生掌握？光凭老师用嘴去讲，难以让学生产生深刻的印象，“百闻不如一见，百看不如一做”，我就设计了多人对比实验，当学生了解萃取的含义后，我仔细讲解了分液漏斗的使用方法，然后用表格展示四个对比实验和实验的步骤，第一个实验是四氯化碳与碘水的萃取；第二个实验是四氯化碳与溴水的萃取；第三个是苯与碘水的萃取；第四个是苯与溴水的萃取萃取。I invited three students to the podium,Take the separatory funnel with the same experiment number,Show the comparison experiment operation with the teacher at the same time,The experimental drugs and instruments are already placed in the experiment box in front of everyone,For all students,We follow the experimental steps for comparative experimental operations,The four of us use the same equipment,The steps are also the same,It's just that the medicines taken are different,In operation,The teacher explained how to hold and use the instrument while operating it,After our operation is completed,Let the students present comment on the experimental operation abilities of the four of us, the problems and the experimental phenomena in the experiment,Questions that appeared in student reviews,Then the teacher will explain.We teachers should not neglect the abilities of students,Through this comparative demonstration experiment,Students have a good grasp of the problems related to extraction experiments in middle schools,Did four experiments at the same time,There are fewer hands-on students,But it is easy to organize teaching and manage students.
When studying the knowledge about alkali metal elements in Chapter 1 of "Compulsory 2",For the change law of the activity of metals of the same main group,The textbook arranges the reactions of sodium, potassium and water,The students were arranged for preview the day before,Students know that there are experiments,Enthusiasm is very high,I talked about doing an experiment,Did not directly let students conduct experiments,Because the experiment is dangerous,Instead, first ask whether the experimental response is violent?Some students checked the experiment online,So when answering the question,Can describe the phenomena, precautions and operating procedures in the experiment more comprehensively,this time,I invited two students who had a better preview to the podium,At the same time, the operation of the comparative experimentOther students in the future preview,Will be more careful and attentive,Of course, the students who have prepared for the experiment do not necessarily have strong hands-on ability.Observing students will have the opportunity to ask questions and their own opinions.Then when learning the declining nature of the elements in the third cycle,I added a comparative experiment,Students who have prepared well have the opportunity to manipulate the reaction of sodium, magnesium, aluminum with hydrochloric acid and water.In class, I asked 6 students to conduct experiments at the same time.As a result of training in the first half of high school,Most students can master the use of test tubes, droppers and alcohol lamps,The teacher only needs to do a little bit,The students can complete successfully,Small problems that arise,All the students here will keep their eyes open and give corrections in time.
When learning the basic nutrients of "Compulsory 2",To learn ① the composition of carbohydrates, fats and proteins; ② the characteristic reactions of carbohydrates and proteins; ③ the hydrolysis reaction of carbohydrates, fats and proteins; ④ the role of carbohydrates, fats and proteins in production and life.This section has a lot of content, scattered knowledge, and many experiments.The syllabus is required to be completed in one lesson,For ①②④students on the basis of preview and experiment,Can successfully complete the compliance exercises,Only the hydrolysis reaction of ③ is the difficulty of teaching,Especially the hydrolysis reaction of sucrose,It involves catalysts, product verification, adjusting the pH of the solution before verification, etc.,How to break through this difficulty in the limited classroom time,I designed a comparative experiment,It was completed by three students in collaboration.During the experiment, the three students took the corresponding labeled test tubes.First, student number ① issued an instruction: "Add a dropper of sucrose solution to the test tube",Three students operated at the same time; student ② issued an instruction: "Add 3 drops of dilute sulfuric acid to the test tube",Only class ② and class ③ did it; after that, all three students put the test tubes into the boiling water that the teacher was heating on the asbestos net.3 minutes later,At the same time, take out the test tube; student No. ③ said while operating: "Add 2 drops of phenolphthalein to the test tube,What color is the solution?oscillation,Then add the sodium hydroxide solution dropwise,why?What happened?Add a drop of sodium hydroxide to make the solution red,The red color does not disappear after shaking,why?"Only student ③ can operate.① Student No. issued the instruction again: "
Take a test tube,取一滴管氢氧化钠溶液，再加入10滴硫酸铜溶液，振荡，倒入水浴过的试管内，在酒精灯上加热。”三位同学都操作。当③号试管出现砖红色时，老师宣布全部停止加热，学生通过对比实验的观察，很容易总结出蔗糖水解的条件，突破了本节课的难点。