Clever thirteen ways to solve chemistry problems plus 100 points or more .

07 Zhejiang preliminary questions.

Original question. 11 points) An experimenter did the following experiment: a certain amount.

CuSO4 solution and solution are mixed to obtain a light green precipitate X. Will.

x isolates the air above 1000 strong heat to obtain a red solid y, and the mass is dissolved in acid to obtain another red solid.

1) The experimenter believes that the precipitate X may contain SO42-. Design a simple experiment to determine this judgment.

2) Determine the chemical formulas of x and y by calculation.

3) The volume ratio of CuSO4 and NaOH solution when mixing is.

Write the reaction equation for x y.

1. Wash the green precipitate X with distilled water many times, until the washing solution can not detect SO42- with BACL2 solution (1 point), dissolve the green precipitate with dilute hydrochloric acid (1 point), and then use BaCl2 solution to test, a large amount of white precipitate is generated in the dissolved solution, which means that there is SO42- (1 point) in the precipitate X

2. Because cu2o cu = points).

Y can be judged to be Cu2O (1 point).

According to the mixture of copper sulfate solution and sodium hydroxide solution to generate precipitation, the precipitate composition can be set to MCU(OH)2·nCuO4, then there is (

m n) points).

This gives m n 3 1 (1 point), so x is 3cu(oh)2·cuso4 or cu4(oh)6so4 (1 point).

3) 4 3 (1 point) Cu4 (OH) 6SO4

2cu2o+3h2o+so3+o2

1. Hypothetical method.

The so-called hypothetical method is to assume that there is a certain type of old piece, deduce a conclusion, compare this conclusion with the actual situation, make a reasonable judgment, and determine the correct option.

2. In the relational method cavity.

In multi-step reactions, the relational method can express the "quantity of matter" relationship between the reactants in the initial state and the products in the final state, simplifying the multi-step calculation into a one-step calculation. Correctly writing relational formulas is a prerequisite for solving chemical calculation problems using the relational method.

3. Difference method.

The key to solving the problem is to find the theoretical difference correctly.

4. Conservation law.

The conservation method "uses a specific quantity to be fixed in the process of material change to solve the columnar solution." Its advantage is that it uses the macroscopic way of controlling the overall situation, does not explore some details, directly grasps the unique conservation relationship, quickly establishes the equation, and solves the problem simply and skillfully. Commonly used methods are conservation of mass, conservation of gain and loss of electrons, conservation of charge, etc.

The problem-solving skills are as follows:

In general, the order in which the devices are arranged should be followed. For the absorption device, if it is a gas washing cylinder, it should be "long" in (conducive to the full absorption of impurities) and "short" out (conducive to gas export); If the drying pipe containing soda lime absorbs water and, it should be "coarse" in and "fine" out (conducive to the export of residual gas); If the amount of water and gas is discharged from the spine, it should be "short" in and "long", and the volume of water to be discharged is the volume of gas generated.

What should I do if I encounter a problem in the middle of the question? Do you have to follow the order from the first to the last? The answer, of course, is no.

If you encounter a difficult topic and still have no idea after a few minutes of thinking, then you should put it aside for a while and start working on other topics, so that you must not waste a lot of time because of one question, so that the later questions cannot be completed with quality and quantity.

Physics and chemistry are unlikely to be mastered at the same level, and there must be relatively advantageous disciplines, so you should adjust your time appropriately when doing the questions: for your own advantageous disciplines, you should answer them as soon as possible in the case of ensuring the accuracy of the evidence, which will save more time for slightly inferior subjects. This will maximize the score.

Select instruments and reagents according to the experimental principle, determine the arrangement and assembly order of the instruments according to the purpose of the experiment, and generally follow the gas system to remove impurities and dry the main body of the experiment and protect the experimental product and treat the exhaust gas. Among them, the order of impurity removal and drying, if the solution is used to remove impurities, it should be purified first and then dried. Tail gas treatment generally uses a solution to absorb or ignite the gas.

The techniques for solving chemical flow problems are as follows:

1. Roughly read the question stem and excavate the diagram.

Focus on keywords, figure out flowcharts, but don't have to push every substance, just ask what pushes what. For example, if you prepare inorganic chemical engineering questions, you can read the test questions roughly to know what the questions are made, the general process and what prompts there are.

2. Carry the question and read the information carefully.

Pay attention to three aspects: one is the backbone, the second is the flow diagram, and the third is the setting problem. Read the trunk and grasp the keywords and words; Read the flow chart, focusing on the flow direction of the substance ("into the car" and "out"), the experimental operation method, etc.

3. Jump thinking and standardize answers.

When answering questions, it should be noted that there is often no "correlation" between the questions before and after, that is, the previous question is not answered, which will not affect the subsequent answers.

Pay attention to the conditions under which each step is in the gods, what reactions occur, what substances are generated, and these substances go to the **. Such as the transformation into precipitation, gas or other substances.

How to solve the problem

1. Beginning and end analysis.

For some linear process test questions, first compare and analyze the first substance and the last substance in the flow chart, find out the relationship between raw materials and products from the comparative analysis, and figure out the basic principles of raw materials into products in the production process and the chemical process of removing impurities, separating and purifying products, and then combine the questions set up to solve them one by one.

2. Segmented analysis method.

For industrial process problems in which two or more products (including by-products) are produced from the same Youxinpai raw materials, it is easier to find the entry point of the problem by using the segmented analysis method.

3. Cross-analysis method.

Some chemical production uses multiple groups of raw materials, first synthesizes one or several intermediate products, and then uses this intermediate product and some other raw materials to produce the required mainstream products, which is suitable for cross-analysis. It is to divide the provided industrial process schematic diagram into several production lines in combination with the preparation principle of common compounds, and then cross analysis up and down.

1.It can be seen that the solute mass is 10g, the mass (solute + solvent) is 35g, the mass fraction w = (10g 35g) * 100% =, the new solution m = m (H2SO4) 10% = 980g, adding water m = m -mo = 880g, the solution mass m = m (HCl) 38% = (1000 volume v = m p (p density) =

Soluble Sino Royal Solution) = 500*, M (Naoh) = 10% * M (Spine Dissolving Solution) = 55g....m(h2o) = m (solution)-m(naoh) = 495g

zn---h2so4

13g---98/65)*13g=

Therefore, m(H2SO4) = in solution

Mass fraction w = m (h2SO4) m (original solution) * 100% = ...... to be continuedSo many questions. It's too little to give???

Redox reactions.

The number of electrons gained and lost is the same.

The total number of valence rises and falls is equal.

Adipic acid is reducible, then adipic acid loses electrons, and VO2+ electrons are completely reacted to a 1:2 relationship according to the title.

The coefficient of VO2+ is 2, and the coefficient of VON+ is 2, and according to the conservation of charge, n=2

When an organic substance undergoes oxidation and reduction reactions, it is calculated by the number of carbon electrons transferred. hon

The valency of X(FCLBR) is set at +1, respectively

1, and then calculate the valency of c according to the sum of the valency of 0 (in organic matter, the valency of c ranges from -4 to +4, sometimes there is a fraction, sometimes there is a 0 valence).

According to the title, 20ml

H2C2O4 (C is +3 valence) is used as a reducing agent, and the C valency can only rise to +4 valence in the reaction (the most ** of C is +4) - C loses 1*2* electrons.

4 10-3mol VO2

v is +5 valence), and the reduced product is vo

n+ (v is 2+n valence).

v gives (5-2-n)*4 10-3mol has 1*2*

5-2-n）*4×10-3mol

The solution is n=2

The C and O mass ratio of CO is 3:4

CO2 has a C and O mass ratio of 3:8

O2 has a C and O mass ratio of 0:32

Obviously, the ratio of the mass of carbon to oxygen of the gas is 3:5 between CO and CO2 or O2, so the answer to this question is ABC

2na + h2o ==2naoh + h2...1)2al + 2naoh + 2h2o ==2naalo2 + 3h2...2)

m(al) = n(al) = =

n2(h2) generated by reaction (2) = *3 = total n(h2) = =

So the n1(h2) = - = generated by the inverse pin should be (1), so the n(na) = * 2 = of Senyou in the mixture, and because there is still n(naoh) = * 2 = so n(na) +2 * n(na2o) = + = so n(na2o) =

So the mass fraction of sodium primitives in this sodium block = 23 * 23 * 2 * 62 * =

I don't know what kind of skill you need, but understanding is the most important thing.

In general, all kinds of techniques can be used, and the most fundamental ones are the most effective.

It can be divided into the following points for analysis:

1. Find the exact relational quantity, including multi-layer reactions and relational reactions such as the chain connection of reactions;

2. Accurate relationship and unit transformation, including the transformation of different types of unit relationships;

3. Accurate calculation.

There are many of them: such as the intake value method, the extreme assumption method, the conservation method, the difference method, the set value to 1 method, the average value method, etc.