How to improve chemistry scores quickly
Strategy 1: combing knowledge
The best way to organize knowledge is to summarize the contents of textbook units, because many middle school questions are adaptations and deformations of textbook exercises, and many of them come from the discussion and exploration of textbook contents. Therefore, when reviewing before the exam, students must pay attention to combing the textbook knowledge, read the key knowledge repeatedly, and don't ignore the details of the textbook content.
We should also strengthen our understanding of key knowledge, including: changes and properties of substances, basic operation of chemical experiments, meanings of chemical terms and expressions, three basic properties and applications of molecules, properties and applications of important substances, law and application of conservation of mass, writing of chemical equations and basic reaction types, solubility curves and applications, application of combustion conditions and fire extinguishing principles, preparation and migration of common gases, sequence and application of metal activity, etc.
Strategy 2: lay a solid foundation
1. Consolidate the foundation. The examination of basic knowledge in the senior high school entrance examination accounts for the vast majority, and it is necessary to remember many basic concepts and principles of chemistry, the properties and uses of substances, etc. Some knowledge must be memorized, but the basic concepts and principles cannot be memorized, so we must understand them thoroughly.
2. Learn to correct mistakes. The biggest enemy in learning is "forgetting". The effective weapons to overcome forgetting are "understanding" and "repetition". Therefore, for the problems you have done, especially the ones you have done wrong, you should find out the root of the mistakes and then find similar problems for intensive training.
3. Strengthen training. In addition to the simulation questions assigned by the teacher, we should also choose the simulation questions according to the local examination syllabus, train the standardization and accuracy of the answers, and ensure that we don't lose points or less during the examination.
Strategy 3: Be familiar with the questions.
For all kinds of questions, especially those that are easy to lose points, we should strengthen targeted training. Among all kinds of questions, the most points lost are short answer questions and experimental inquiry questions, which are mainly introduced here.
Answer the short answer questions well: 1. Clear your mind, only by clarifying the cause and effect can you answer accurately. 2. The language should be accurate, and you can't answer by subjective imagination and guess. 3. Language should be standardized. Common mistakes include typos in special nouns, improper words (such as writing "burning" when the condition is "lighting") and unclear expression (such as writing "colorless" as "white").
For open-ended short answers, we should focus on the theme and answer them with the knowledge and life experience we have learned. Short answers that are often designed to be open-ended include: the causes of air and water pollution and its prevention measures, the measures to prevent "greenhouse effect" and "white pollution", some concrete measures to save water and low carbon life, the causes and prevention measures of steel corrosion, etc.
In the experimental inquiry questions, the most lost points are the experimental schemes designed by ourselves, and many students don't know where to start. There are three main points to grasp: first, write down the steps of experimental operation, including sampling and adding reagents; The second is to specify the expected experimental phenomenon; The third is to draw conclusions according to the phenomenon. The designed experiment should be simple and clear.
Strategy 4: Cultivate ability
Every year, some basic chemical ideas and problem-solving methods will be examined in the chemistry test questions of the senior high school entrance examination, which requires students to pay attention to the cultivation of chemical ideas and problem-solving methods when reviewing. Common ones are: 1. The idea of material classification. Investigate the classification of substances according to certain laws and the judgment of right and wrong in chemical research. 2. Green environmental protection thought. Check whether the environmental pollution problem is considered when designing the experiment, and what measures should be taken to solve it if it causes pollution. 3. Thought of conservation of element mass. The mass of any element is constant before and after the chemical reaction, that is, the total mass of an element in each reactant is equal to its total mass in each product. At present, China is vigorously carrying out the activities of practicing economy, increasing income and reducing expenditure, and avoiding extravagance and waste. This year's senior high school entrance examination may also include this idea in the examination questions.
The characteristics of information interpretation questions are:
The information in (1) is enlightening and can be fully utilized.
(stem information is often new knowledge or new situations that students have never learned.
(3) Information is provided in various forms, some in the form of written materials, some in the form of tables and charts, and some in the form of labels.
(4) It is comprehensive and covers a wide range, including information on life and production as well as high-tech fields.
The steps to solve the problem of information interpretation are: carefully examining questions, obtaining information → refining information, discovering laws → adapting to new situations and solving problems. Solving problems is not only mechanical imitation, but also random play. We should give full play to our imagination, transfer the laws of learned knowledge to new information, grasp the characteristics of information, link "new" and "old" knowledge, and creatively use analogical reasoning to solve problems.
The proposition trend of information interpretation questions can be roughly divided into the following categories:
(1) Take high school chemistry knowledge as a new information proposition.
(2) Take the chemical knowledge contained in new science and technology and new concepts as a new information proposition.
(3) Take social hot issues as new information propositions.
(4) Take some examples from actual production and life as new information propositions.
(5) Evolve textbook knowledge and laws into new information propositions.
Question type 1. Direct application information problem
The information involved in this kind of information interpretation questions is generally closely combined with the frontier problems of production, life or science and technology, as long as the learned knowledge is directly applied to new situations.
Example 1 (Meishan, 20 15) Observe the chart 1 and answer the questions:
As can be seen from the figure, the reaction between HCl and NaOH is essentially the reaction between H+ and OH-, namely:
Oh, H2O
A formula like this, in which ions actually participate in the reaction, is called ionic equation. Any metathesis reaction can be represented by ionic equation.
According to the requirements of writing chemical equations, practice writing ionic equation of the following reactions.
Reaction between HCl solution and AgNO3 solution:. Reaction between nitric acid solution and sodium carbonate solution:.
The essence of induced metathesis reaction is: the reaction produced by the combination of anion and cation.
Judging from the application, a large number of ionic groups can exist in the aqueous solution.
A. sodium, hydrogen, chlorine, carbon dioxide, hydrogen, barium, chlorine and sulfate
C copper ions, sodium ions, nitrate ions, hydroxide ions, potassium ions, chloride ions and sulfate ions
The reaction between hydrochloric acid and silver nitrate solution was analyzed to produce silver chloride precipitate and nitric acid. The essence of the reaction is that Ag+ reacts with Cl- to produce silver chloride precipitate. Nitric acid reacts with sodium carbonate solution to produce sodium nitrate, water and carbon dioxide. The essence of the reaction is that H+ reacts with CO2-3 to produce water and carbon dioxide. The condition of double decomposition reaction is that two substances exchange components such as precipitation, gas or water, and the essence of double decomposition reaction is that anion and cation combine to produce precipitation, gas and water. H+ and CO2-3 in tank A combine to form water and carbon dioxide, which cannot be stored in large quantities; Ba2+ and SO2-4 in B can combine to form barium sulfate precipitate, which cannot be stored in large quantities. Cu ~ (2+) and OH- in C can combine to form copper hydroxide precipitate, which cannot be stored in large quantities. The four ions in D can't combine to form precipitation, gas or water, but they can exist in large quantities.
Answer:
Ag++Cl-AgCl↓
2H ++ CO2 -3 CO2 =+H2O
Precipitation, gas or waterd
Answering this kind of information questions requires students to have certain reading comprehension ability, and can quickly and accurately screen and extract available information on the basis of reading comprehension.
Question 2: Analogy analysis information problem
This kind of information interpretation questions are generally based on the learned knowledge, building a platform and connecting it with the new information in the stem, so as to examine the analogy and analysis ability of familiar and unfamiliar materials.
Example 2 (Shenyang, 20 15) Simple silicon can be made from silicon oxide, and the main chemical reactions are as follows:
Preparation of crude silicon;
Silicon dioxide (quartz sand) +2C (coke) high temperature electric furnace
Si (coarse silicon) +2co =
Making pure silicon from crude silicon (common method);
Si (coarse) +2Cl2 high temperature SiCl4
SiCl4+2H2 high temperature silicon (pure) +4HCl
(1) According to the above information, please complete the simple flow chart for preparing pure silicon:
Quartz sand coke, high-temperature crude silicon Cl2, high-temperature H2 and high-temperature pure silicon.
(2) According to the existing knowledge and the above information, summarize:
① The general formula for completing the displacement reaction is:
Element I+compound I+element II.
② Fill in the form 1:
Analysis (1) From the main chemical reactions in the title, it can be seen that the process that needs to be completed is that crude silicon and chlorine gas are heated to generate silicon tetrachloride. (2)① Displacement reaction is a reaction in which a simple substance reacts with a compound to generate another simple substance and another compound, which can be expressed as: simple substance I+ compound I+ compound II. (2) The simple substance I in B is copper, which can react with the salt solution of the metal whose metal activity sequence is after copper. For example, copper reacts with silver nitrate solution to generate copper nitrate and metallic elemental silver. According to the material classification of elemental Ⅰ and Ⅱ of A, B and D provided in the table, it is inferred that elemental Ⅰ and Ⅱ in C are nonmetals. Non-metallic element carbon can react with silicon dioxide to produce carbon monoxide and non-metallic element silicon, that is, the chemical reaction to produce crude silicon in the title. According to the chemical equation given in D, simple substance II is metal and simple substance I is nonmetal.
Answer: (1) silicon tetrachloride (or sicl4);
(2)① Compound Ⅱ (or compound) ②Cu+2AgNO3Cu(NO3)2+2Ag (reasonable) nonmetal SiO2+2C high temperature electric furnace Si+2CO↑ = (reasonable) nonmetal.
This topic mainly examines the significance of substitution reaction and the writing method of chemical equation. When writing chemical equations, we must follow the law of conservation of mass. The key to solve this kind of information problem is to extract valuable information. If the information is found correctly, the problem will be solved.
Question 3. Information problems about knowledge transfer
There is generally no obvious direct connection between the information given in this kind of information interpretation questions and the stem of the questions. We must boldly transfer existing knowledge to new knowledge, so as to acquire new knowledge.
Example 3 (Linyi, 20 15) Please analyze the experimental device in Figure 2 and learn the materials provided.
Experimental device:
Figure 2 Learning materials: Ammonia (NH3) is a colorless gas with pungent smell, less dense than air and easily soluble in water. Ammonia can turn wet red litmus paper blue. Ammonia [2nh4cl+Ca (OH) 2 △ CaCl2+2nh3 ↑+2H2O] can be prepared by heating with ammonium chloride and hydrated lime in the laboratory.
Ammonium salts are easily soluble in water. Ca(OH)2 is slightly soluble in water. Silver chloride (AgCl) is a white solid which is almost insoluble in water. CaCl2 solution is neutral and NH4Cl solution is acidic.
Please answer:
(1) The name of instrument A is and the name of instrument B is.
(2) When KMnO4 is used to produce oxygen, device A should be selected. The reason for choosing device a is.
(3) In order to prepare and collect ammonia in the laboratory, the selected generating device is (fill in the device number, the same below) and the collecting device is. Check whether the ammonia is completely collected.
A classmate made a further study on the solid matter in the reactor after ammonia production reaction:
(1) Put a small amount of solids in the reactor in a test tube, add water to dissolve, and filter to obtain filtrate.
(2) Take a small amount of filtrate in a test tube, and drop colorless phenolphthalein solution into the test tube. The color of the solution has not changed, indicating that the solid matter does not contain Ca(OH)2.
③ Put a small amount of filtrate into a test tube, and add AgNO3 _ 3 _ 3 solution into the test tube dropwise to produce white precipitate. The student concluded that solid matter must contain NH4Cl.
Do you think the conclusion that "solid matter must contain NH4Cl" is correct (fill in "Yes" or "No")? The reason is.
The analytical instrument (1) A is a long-necked funnel and B is a conical flask. (2) The reactant for preparing oxygen in device A is solid, and the reaction condition is heating. Therefore, when preparing oxygen with KMnO4, device A should be selected. (3) The reactant of ammonia production in the laboratory is solid, and the reaction condition is heating, so the selected generator is A; Ammonia is less dense than air and easily soluble in water, so the collection device is D; Ammonia can make the wet red litmus test paper blue, so the operation method to check whether the ammonia water is completely collected is to put the wet red litmus test paper on the bottle mouth, and the blue test paper proves that it is completely collected. Ammonium chloride and calcium hydroxide are heated to generate calcium chloride, ammonia water and water, phenolphthalein turns red when it meets alkali, and chloride ion and silver ion will generate silver chloride precipitate, so this conclusion is incorrect, because calcium chloride will generate white precipitate with silver nitrate.
Answer: (1) long-necked funnel conical bottle;
(2) the reactant is solid, and the reaction condition is heating;
(3)A D Put the wet red litmus test paper on the bottle mouth, and the test paper turns blue, which proves that if it is filled with calcium chloride, it will also generate white precipitate with silver nitrate.
Through experimental data and exploration, this topic mainly investigates the selection of common gas generating devices and collecting devices. The generator is selected according to the state of reactants and reaction conditions, and the collector is selected according to the density and solubility of gas.
Question 4. Information problems, such as charts, tables and labels
When solving this kind of information interpretation problem, we should use the new knowledge obtained from charts, tables or labels to connect with the existing knowledge to solve the problem.
Example 4 (Shanxi, 20 15), as shown in fig. 3, shows the microscopic changes of water vapor liquefaction, charged decomposition of water and combustion of hydrogen in chlorine.
Please answer the following questions:
The chemical equations shown in Figure 3( 1) and Figure ② are as follows:
(2) Explain the essential difference between Figure ① and Figure ② from the microscopic point of view.
(3) From Figures ② and ③, it can be concluded that the particles that must remain unchanged in chemical changes are molecules that may change.
(4) Another piece of information that can be obtained from Figure ③ is.
Analysis (1) Figure ② shows that one compound generates two simple substances, which is the process of electrolyzing water. (2) Figure ① shows the process of water vapor liquefaction, in which only the state of water has changed, and no new substance is generated, which belongs to physical change; Figure ② shows the process of electro-decomposition of water, in which water decomposition produces new substances: hydrogen and oxygen, which belong to chemical changes. From the microscopic point of view, the essential difference between them lies in the substance composed of molecules. In physical changes, the molecule itself does not change, while in chemical changes, the molecule itself changes and becomes the molecule of other substances. (3) Figures ② and ③ show the process of chemical change. In chemical changes, molecules can be split into atoms and atoms can be recombined into new molecules. Before and after chemical changes, the number of atoms must remain the same, while the number of molecules may change. (4) Figure ③ shows the process of chemical change, and the types of elements will not change before and after chemical change.
Answer: (1)2H2O charged 2H2 ↑+O2 ↑;
(2) Molecules remain unchanged in physical changes and change in chemical changes;
(3) number of atoms (or total number; Or numbers);
(4) The element types are unchanged before and after the chemical reaction (as long as it is reasonable)
This topic mainly investigates the microscopic model representation of chemical reactions. To complete this topic, the key is to fully understand the information in the diagram according to the nature of the reaction and the structure of the model. Only in this way can we make a correct judgment on the problem.
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