The problem of acid, alkali, salt and oxide synthesis (3)-inference problem

2. Teaching emphases and difficulties

Master the solutions to the comprehensive problems related to impurity removal, identification and inference.

[Example 1] Some substances harmful to human body are often dissolved in the sewage discharged from chemical plants. Visually, it is preliminarily considered that it may contain Fe3+, Ba2+, Na+, OH-, Cl-, CO32-and SO42-; In order to further confirm, carry out experimental tests:

(1) Take the sewage for careful observation. It is colorless, transparent and uniform.

(2) Dropping dilute sulfuric acid into the sampled sewage will produce a lot of white precipitate. When dilute nitric acid is added, the white precipitate will not disappear.

(3) Determine the pH value of sewage with pH test paper, and the test paper is dark blue. Therefore, sewage must contain ions. There must be no ions, but there may be ions.

(4) Some soluble compounds are dissolved in water by the extracurricular activity group of a school to prepare two solutions, A and B. * * * contains H+, Ag+, K+, Ba2+, OH-, Cl-, NO3-and Co32-8 ions, and the two solutions contain different ions. It is known that litmus test solution is dropped into solution a.

Analysis: This topic is called Narrative Inference Question, which can determine or exclude targets one by one according to the information given in the question. From (1), the sewage is colorless and transparent, so we can know that there must be no Fe3+. If Ba2+ exists, CO32-and SO42- do not exist; By (3) knowing that the solution is alkaline, we can be sure that the ions contained are OH-, Na+ and Cl-, so we can't judge. (4) Dropping litmus test solution into solution A turns blue, indicating that solution A contains OH-, then there are H+, Fe3+ and Ag+ in solution B. Because Ag+ and Cl- and Co32- cannot exist, Cl- and Co32- are both in solution A. In order to ensure the electrical neutrality of solution A, solution A needs to contain cations, which can only be. Then the ions contained in solution B are H+, Ag+, Ba2+ and NO3-.

[Example 2] When X is gradually added to the device shown in the figure below, the balloon can be observed to expand gradually; Then gradually add y, and see that the balloon is getting smaller. X and y are () in turn.

A. hydrochloric acid and sodium sulfate solution B. hydrochloric acid and calcium chloride solution

C. sulfuric acid and barium hydroxide solution

Analysis: "After adding X, the balloon expands gradually", which shows that X can react with Na2CO3 to produce gas. "After adding Y, the balloon gradually becomes smaller", which means that Y can react with the gas produced in the previous reaction, so that the gas quantity is reduced. In options A, B, C and D, hydrochloric acid and sulfuric acid can react with Na2CO3 solution to generate carbon dioxide gas, while in option Y, only Ba(OH)2 solution can react with CO2, that is, CO2+BA (OH) 2 = baco3 ↓+H2O, and this reaction does not generate gas, so C meets the requirements.

Answer: c

[Example 3] There are six substances A, B, C, D, E and F in the picture below. They are five solutions of copper nitrate, sodium carbonate, barium chloride, dilute sulfuric acid, calcium hydroxide and elemental iron. A chemical reaction will occur between two substances connected by a straight line.

(1) Inference: B is.

(2) The chemical equation of the reaction between C and F is.

Analysis: this question belongs to the connection inference question, suggesting that a chemical reaction can occur between two substances connected in a straight line. First observe how many lines each substance emits, indicating that it can react with several substances. A, C:4, B, D:3, E, F:2. Let's see how many reactions each given substance can have. The ratio of copper nitrate, calcium hydroxide, sodium carbonate, sulfuric acid, barium chloride and iron is 3:4. And then speculate. If e is BaCl2, Na2CO3 and H2SO4 that can react with it are A and D, respectively. The figure shows that A and D have 4 or 3 reactions respectively, which is obviously inconsistent with Na2CO3 and H2SO4. Therefore, if E is f E, H2SO4 and Cu(NO3)2 that can react with E are A and D respectively. It is further inferred that F is BaCl2, C is Na2CO3, and B is Ca.

Answer:

(1)B is

(2) The chemical equation of the reaction between C and F is Na2CO3+ BaCl2= BaCO3↓+ 2NaCl.

[Example 4] The following is an experimental scheme for students to remove a small amount of Na2SO4 and Na2CO3 mixed in NaCl crystals:

Try to answer according to the above experimental scheme:

(1) gas e is

(2) write the chemical formula: x y.

(3) The composition of solid A is:

The composition of solid c is:

(4) There are two filters in the above scheme, whether they can be combined into one filter (select Yes or No).

Analysis: This problem is a combination of inference and impurity removal. The purpose of this problem is to remove Na2SO4 and Na2CO3 from NaCl. However, the reagents added in the process of impurity removal must be combined with the idea of inference in order to break through the difficulties one by one. In the process of inference, we should always pay attention to the phenomenon caused by adding reagents as the basis for judgment. In addition, as an impurity removal operation, the dosage selection of added reagents is also a piece of information to assist inference. In addition, the flexible use of forward and backward methods is also helpful to solve the problem.

From the fact that gas E can make clear limewater turbid, we can know that E is CO2, and the solution is heated and evaporated to dryness to obtain pure NaCl crystals. It can be known that NaCl of solute in F must contain Na2CO3 in D solution. ..

When NaCl contains Na2SO4 and Na2CO3, when excessive X solution is added after dissolution, solid A and solution B will be generated, then X can remove SO42-and CO32-impurities at the same time, and the newly introduced anion can only be Cl-, so it can be inferred that X is BaCl2, solid A contains BaCO3 and BaSO4, and filtrate B is NaCl solution containing excessive BaCl2 and impurities. If excessive Y solution is added to produce solid C and filtrate D, then Y will be able to remove Ba2 ++ and introduce Na+ at the same time, then Y will be Na2CO3 solution, solid C will be BaCO3, and filtrate D will be NaCl solution containing excessive Na2CO3 impurities. After adding a proper amount of Z, the product is obtained, and Z is HCl solution.

During the operation, the precipitate produced by adding X and Y to dissolve again has no reaction, so the two filtrates can be combined.

Answer:

(1) carbon dioxide

(2)X: barium chloride, y: sodium carbonate

(3)A:BaCO3，BaSO4 C:BaCO3

(4) Yes

[Example 5] At present, three soluble normal salt solutions A, B and C are tested as shown in the following figure, and A and B, B and C all react completely.

Try to infer: (write chemical formula or ion symbol)

Solution a is, and precipitate b is.

Solution b is, and precipitation f is.

The solute in filtrate e is.

The anions that must be contained in filtrate h are.

Analysis: This problem can be analyzed by forward reasoning and backward reasoning. From the reaction of A and B, B and C, white precipitate insoluble in dilute NHO3 can be produced. B is known as BaCl2, white B is produced when E is added with C, and blue precipitate F is known as Cu(OH)2. If there is Cu2+in E, it must come from C or D, so A and C are AgNO3 or CuSO4 respectively. Cu(OH)2 is formed by mixing C and D and adding excessive butyl. If C and D contain Cu2++, butyl will be alkali, if E contains the same cation, it will be ag+ or Ba2++, but AgOH is impossible, and butyl will be.

Answer: a: agno3b: baso4 b: BaCl2 F:

e:、BaCl2 H:NO3-、Cl-

1. It is known that A is an alkaline solution and B is a chloride solution, with the following changes, as shown in the following figure:

Write the chemical formulas of A, B, C, D and E according to the above changes:

A B C D E

2. There is a colorless mixed gas, which may be composed of one or more gases in and. When this mixed gas is introduced into excessive clarified limewater, there is no turbidity, but the total volume of the gas is obviously reduced. When the residual gas passes through concentrated sulfuric acid, hot copper oxide and anhydrous copper sulfate in turn, it is observed that black copper oxide turns red and anhydrous copper sulfate turns from white to blue (hydrogen chloride is a colorless gas, which is easily soluble in water, and 1 volume of water can dissolve 500 volumes of hydrogen chloride gas.

Infer:

(1) Reasons for the obvious decrease of mixed gas (write chemical equation).

(2) Anhydrous copper sulfate changes from white to blue (write the chemical equation).

(3) The gas that must be contained in the mixed gas is; The gas that must be absent is; There may be gas.

3. The waste liquid in the laboratory may contain one or more of ferric chloride, sulfuric acid, sodium sulfate, sodium chloride, sodium hydroxide, sodium carbonate and barium nitrate. The students in the chemistry extracurricular activity group of Grade Three conducted the following experiments on the waste liquid:

(1) Take the waste liquid and observe that it is a colorless solution;

(2) Take a small amount of waste liquid, add barium chloride solution dropwise, and white precipitate will appear, and continue to add dilute nitric acid without obvious phenomenon;

(3) Take a small amount of waste liquid and add iron powder to generate a large number of bubbles.

According to the above experimental phenomena, it can be inferred that the waste liquid definitely contains, definitely does not contain, and it is uncertain whether it contains.

4. The numbers A, B, C, D, E and F6 in the figure below respectively represent one of the following substances, and any two adjacent substances can be chemically reacted when they are connected in a straight line. The substances to be filled in the box are: sodium carbonate solution, zinc sulfate solution, barium chloride solution, dilute sulfuric acid, iron and copper nitrate solution. Fill in the chemical formula of the corresponding substance in the box.

5. Four compounds, namely A, B, C and D, are composed of two or three elements of H, O, Na and S respectively. A can react with it to form two salts; B can react with salt and water; Propane can react with hydrochloric acid to produce salt and water; Butyl is neutral and reacts with alkali and acid to produce alkali and acid respectively. Then make the following four judgments: (a) A may be; (b) B must be; (c) C must be; (D) It must be D. The correct answer is

(Fill in serial number).

6. In solution A and solution B respectively, * * * contains six kinds of ions, and the ions contained in the two solutions are different. It is known that solution A contains one cation and two anions, and the rest is in solution B, so the ions contained in solution A are: The ions contained in solution b are.

7. In the two solutions A and B held separately, * * * includes

There are seven kinds of ions, and the two solutions contain different ions. It is known that solution A contains three cations and two anions, and the rest is in solution B, so the ions contained in solution A are: The ions contained in solution b are.

8. There are six substances, namely calcium hydroxide, iron, barium nitrate, dilute hydrochloric acid, soda ash and copper sulfate. Fill in their chemical formulas in the six boxes below, so that all the connected substances can react chemically.

9. A pack of white powder may be one or two of barium chloride, potassium carbonate, calcium carbonate and sodium sulfate. Dissolve them in water to form a white precipitate. After filtration, hydrochloric acid was added to the precipitate, which completely dissolved and released gas. Adding dilute sulfuric acid to the filtrate will produce white precipitate. The chemical formula of the substance contained in white powder is.

10. There are six compounds A, B, C, D, E and F and two simple substances A and B, in which C is a salt compound, and they have the following transformation relations under certain conditions: A+A+B; d+A→C+B； C+e → f (reddish brown)+

Determine the two substances A and D (write the chemical formula): A; d .

1 1. A solution contains four kinds of ions, in which the ion number ratio is, if the ion number is 4a, the ion number is.

12. When identifying and purifying substances in the laboratory, appropriate reagents must be selected. If you want to distinguish between lime water and caustic soda solution, you can choose (only fill in one). Remove a small amount of ferric sulfate from sodium nitrate solution. If only one reagent is allowed, it should be selected. The ionization equation of this reagent in solution is: If both reagents can be used, and should be selected.

13. Fill in the chemical formulas of charcoal, carbon dioxide, copper oxide and calcium hydroxide in the box below, so that the substances in every two boxes (including solutions) connected by line segments can react with each other.

Write the equation that satisfies the following conditions in the material reaction in the figure below:

(1) combination reaction

(2) Displacement reaction

(3) Displacement reaction

14. Add a certain amount of dilute sulfuric acid into a beaker filled with a solid mixture of magnesium, copper oxide and sodium hydroxide, filter after full reaction, and then drop a few drops of phenolphthalein test solution into the filtrate. When the phenolphthalein test solution turns red, the solute contained in the filtrate is.

15. It is known that colorless solutions may contain several of the eight ions, and so on. Take a little of this solution and drop a few drops of litmus test solution, and the litmus test solution turns red, so a large number of ions in the original solution may be.

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