2005. 1. 15. Shanghai

The competition time is 4.5 hours. Those who are more than 30 minutes late may not enter the examination room. You are not allowed to leave within 1 hour after starting the exam. Time is up, put the test questions and answer sheets in an envelope, put them on the desktop, and leave the examination room immediately.

Test papers and answer sheets shall be bound into volumes and shall not be disassembled. All answers must be written in the position specified on the answer sheet; Answer the questions with a black ink pen or ballpoint pen. Don't bring any other paper into the examination room. You can raise your hand and ask the invigilator for additional answer sheets or draft paper. Fill in the total number of pages and page numbers in the header of the answer sheet.

You must fill in the camp number and name in the designated position on the left side of the first page of the test questions and the left side of the answer sheet on each page, otherwise it will be regarded as waste paper.

It is allowed to use unprogrammed calculators, rulers and other stationery. Pencil boxes and communication tools are not allowed to enter the meeting place.

Question 1 (8 points)

White crystal X is produced by the reaction of concentrated sulfuric acid and urea. X does not contain crystal water, does not absorb moisture, is soluble in water, and its molar mass is less than 100g? Mol- 1 is widely used, such as papermaking, textile, electroplating, water treatment, organic synthesis and so on. For field geologists, it is much more convenient to identify limestone than hydrochloric acid. Under acidic conditions, 1 mol x reacts with excess sodium nitrite aqueous solution to release 1 mol nitrogen, and then excess BaCl2 aqueous solution is added to generate 1 mol BaSO4 precipitate.

1- 1 Write the structural formula and chemical name of X. (If you can't write the structural formula, you can ask the invigilator for an answer, but 2 points will be deducted on the spot; You should still answer this question.

1-2 Write the chemical equation of X above.

1-3 Write the chemical equation of the reaction between X and sodium nitrite under acidic conditions.

In a nearly neutral solution, 1 mol of periodic acid reacts with excess iodide to generate 1 mol of I2, and the resulting solution is acidified to generate 3 mol of I2.

1-4 uses an equilibrium chemical equation to illustrate the above phenomenon.

In the later stage of oil and gas well exploitation, it is generally necessary to inject water to exploit deep oil and gas. After a period of time, organic solvents such as methanol are often injected to produce more oil and gas.

1-5 Briefly describe the function of methanol injection.

Question 2 (6 points)

2- 1 Draw trans-dichloro on the empty template given on the answer sheet? Structural formulas of all geometric isomers of bis (2,3-butanediamine) cobalt (Ⅲ) ion. (Note: 2,3-butanediamine is also called 2,3-diaminobutane)

2-2 represents an optically active isomer.

2-3 It is known that chlorine in one isomer is replaced by other negative monovalent anions at the slowest rate. What kind is it? How to understand its essence?

Question 3 (10): At present, almost all the positive electrodes of commercial lithium-ion batteries are lithium-cobalt composite oxides, and their ideal structures are shown in Figure 3- 1 on the answer sheet.

3- 1 Draw the unit cell of the ideal structure of lithium cobalt composite oxide crystal with thick frame on Figure 3- 1 of the answer sheet.

3-2 How many lithium atoms, cobalt atoms and oxygen atoms are there in a unit cell of this crystal?

3-3 gives the chemical formula (the simplest chemical formula) of this ideal structure lithium cobalt composite oxide.

3-4 Lithium-ion batteries must be charged for a long time before they can be used. Write the electrode reaction when lithium cobalt oxide is used as positive electrode discharge.

3-5 lithium manganese composite oxide is another cathode material for lithium ion batteries. There are two kinds of polyhedrons in the ideal crystal: LiO _ 4 tetrahedron and MnO _ 6 octahedron, the number ratio is 1: 2, the LiO _ 4 tetrahedron is separated from each other, and all the oxygen atoms of MnO _ 6 octahedron are taken from LiO _ 4 tetrahedron. Write the chemical formula of this crystal.

3-6 Get information from the following figure to explain why lithium ions in the crystal can move in the crystal when the cathode material of lithium manganese oxide is charged and discharged, and the quantity is variable. The influence of the increase or decrease of lithium ions in the crystal on the oxidation state of manganese is also explained.

Figure 3-2 Schematic diagram of ideal crystal structure of lithium-manganese composite oxide cathode material

Question 4 (6 points) The content of Al3+ in Cu2+ and Zn2+* * can be determined by EDTA coordination titration. With PAN as indicator, the relative error of determination is ≤ 0.65438 0%. The determination process can be expressed as follows (note: the number of complex charges in the table is omitted; Various forms of free EDTA are abbreviated as y):

Attachment: logarithmic lgK stability data of complex stability constant;

CuY 18.8 ZnY 16.5 AlY 16. 1 alf 63- 19.7 Cu-PAN 16

4- 1 Write the reaction formula from D-frame state to E-frame state and balance it.

What other substances should exist in the state of frame 4-2 F?

4-3 Is it necessary to know the exact concentration of EDTA solution used? Does V 1 need to be accurately read and recorded?

Briefly explain why.

4-4 If the Cu2+ solution drops excessively from frame C to frame D, ask:

(i) Will a positive error or a negative error be introduced into the final determination result? Still no effect?

(2) If you think it has an impact, how should you handle the experiment?

4-5 let the sample volumes V0 and V 1, V2 and V3 All take mL as the unit, and MAl is the molar mass of al (g? Mol- 1), c(EDTA) and c(Cu) are the concentrations of EDTA and Cu2+ solution (mol? L- 1), list the Al content in the test solution (g? L- 1)。

Question 5 (6 points) Atoms (groups) in isomeric molecules have specific orientations in space, which makes it possible to show that enantiomers are not coincident with their mirror images. This molecule is called a chiral molecule.

It is known that the sign of the optical rotation of (R-)CHBrClF can be represented by (+). Which of the following four structural formulas (1~4) is left-handed?

5-2 Point out the achiral compounds in the following compounds, and briefly describe their achiral reasons.

5-3 arsines with three different substituents, such as CH3As(C2H5)(C6H5CH2), have optical activity, while amines with three different substituents, such as CH3N(C2H5)(C6H5CH2), have no optical activity. Why? However, optically active amines with similar 1 structure can exist stably again. Why?

Question 6 (8 points) Formaldehyde is also called "formaldehyde". The aqueous solution containing 37-40% formaldehyde and 8% methanol is commonly known as "formalin". Formaldehyde is an important organic synthetic raw material, which is widely used in the production of resin, synthetic fiber, medicine, paint and disinfection of houses, furniture and seeds.

Answer the question with the data given in the table below (let Δ δH m? With Sm? Does not change with temperature).

Thermodynamic data of some substances (298. 15 K)

Material fH m? /kJ？ mol- 1 Sm？ /J？ K- 1？ Mol-1

Ethanol (g) -235. 10 282.70

Methanol (g) -200.66 239.8 1

HCHO(g)- 108.57 2 18.77

H2O(g)-24 1.8 18 188.825

Carbon monoxide (g)-110.525197.674

Ag2O(s)-3 1.05 12 1.3

Silver 0 42.55

H2 0 130.684

Oxygen (g) 0 205. 138

Dehydrogenation of 6- 1 methanol is the simplest industrial method to produce formaldehyde;

Methanol oxidation is another industrial method to produce formaldehyde, that is, methanol vapor and a certain amount of air pass through Ag catalyst layer, and methanol is oxidized to obtain formaldehyde;

Through simple thermodynamic analysis, the above two methods were evaluated at 298.438+05 K.

6-2 In fact, the reaction of methanol oxidation to formaldehyde is the combination of methanol dehydrogenation and hydroxide combination. Try to analyze the practical significance of the combination of these two reactions to the formation of formaldehyde through calculation.

Figure 6-3 on the right shows the lgK of methanol-formaldehyde related reaction. It changes with the temperature t, please indicate which chemical reactions the curves (1), (2) and (3) in the figure correspond to respectively. Why?

The related reaction is:

And the inevitable deep oxidation reaction in the oxidation process:

When 6-4 is oxidized to formaldehyde, the mixture of methanol and air at 550℃ and total pressure 10 1325 Pa passes through the silver catalyst, and the silver gradually loses its luster and breaks. Try to judge whether the above phenomenon is caused by the oxidation of Ag to Ag2O(s) by calculation.

Carbon monoxide and H2 can synthesize 6-5 methanol. At 500℃ and 25 MPa, in the presence of ZnO-Cr2O3-Al2O3 catalyst, the synthesis gas with the volume ratio of CO and H2 of 1∶2 has the following two parallel reactions ① and ②:

Try to calculate the molar fraction ratio of equilibrium products CH3OH and C2H5OH.

Question 7 (6 points) Chemical reactions are generally composed of several elementary reactions, so in principle, the rate equation of the reaction can be established through the reaction mechanism. In scientific research, the reaction mechanism is usually assumed based on practical experience, and then the correctness of the reaction mechanism is verified by various experimental methods and means.

The decomposition reaction of nitroamide in aqueous solution is as follows:

NO2 NH2 N2O (g)+H2O

The experimental results show that the rate equation is:

7- 1 Some researchers have proposed the following three reaction mechanisms, which one do you think is more reasonable? And write the expression of k.

①NO2·NH2·N2 O(g)+H2 O

② NO2 NH2+H3o+NO2 NH3+H2O (reaching equilibrium instantly)

NO2 NH3+ N2 O(g)+H3O+ (slow reaction)

(3) NO2 NH2+H2O+H3o+ (instantaneous equilibrium)

N2 O(g)+ (slow reaction)

H3O++2H2O (rapid reaction)

7-2 In the buffer medium with constant experimental temperature and pH, the reaction is carried out in a closed container, and the measured data of pressure P of N2O gas changing with time are shown in the following table:

t/min 0 5 10 15 20 25 *

Pressure/kPa 0 6.8012.4017.20 20.80 24.00 40.00

The half-life t 1/2 of the decomposition reaction was found, and it was proved that lg t 1/2 had a linear relationship with the pH of the buffer medium.

Question 8 (10) Artemisinin was extracted from Artemisia annua by scientists in China in 1972, and its structure was confirmed in 1976. According to a paper published in the British journal Nature in August 2003, artemisinin has a short half-life, and it is difficult for plasmodium to develop drug resistance through direct interaction with the cell membrane of plasmodium. In addition, artemisinin has no side effects caused by quinine, a commonly used antimalarial drug. Artemisinin, an artemisinin drug developed by China, won the highest medical award in Thailand in 2004. The structural formula of artemisinin is shown as 1.

What are the functional groups in 8- 1 artemisinin?

How many chiral carbon atoms are there in the molecule of 8-2 artemisinin?

The total synthesis of 8-3 artemisinin was also completed by researchers in China for the first time. According to the given reaction process, the reaction reagents represented by A, B, C, D, E, F, G, H, I and J are written.

What kinds of chemical reactions are involved in the last step of 8-4 total synthesis from 10 to 1?

2005 National Chemistry Competition for Senior High School Students

2005. 1. 16. Shanghai

Camp number

Extraction of magnesium sulfate heptahydrate from salt mud

Precautions:

1, total score of experimental examination 100. The experimental examination paper includes "experimental questions" and "experimental reports". The sixth page of the experiment questions is distributed by the invigilator one by one.

2, the experimental examination time is 5 hours, every more than 5 minutes deducted 3 points, the longest shall not exceed 20 minutes. Please read the content of the test questions carefully and arrange the time reasonably. You can process the data with your own calculator.

Please check the instruments provided before the experiment, and report any questions to the invigilator.

4. If you fail to prepare the experiment, you can ask the invigilator to analyze the product, but you should deduct 30 points. If the preparation experiment is repeated, 10 will be deducted for each raw material request. In the analysis experiment, 3 points will be deducted for one less parallel determination, and 2 points will be deducted for weighing 1 time.

5. The invigilator's signature is required, and the candidates must actively cooperate. The experimental results of those who have not signed are considered invalid. Those who falsify data will be counted as zero.

6, pay attention to safety, must wear protective glasses and gloves.

7. Wastes and recovered solvents should be put into designated containers.

8. After completing all the experimental contents, hand over the products, experimental reports and experimental questions to the invigilator, and the invigilator will sign them. Before leaving the examination room, clean the instrument and tidy up the desktop (cleaning time is not included in the experimental time).

First, the experimental content

Salt mud is the waste residue of chlor-alkali industry, which can be divided into primary salt mud and secondary salt mud. Primary salt mud contains magnesium, calcium, iron, aluminum, manganese silicate and carbonate, in which magnesium (calculated as Mg(OH)2) is about 15%. This experiment requires extracting magnesium sulfate from primary salt mud. 7H2O .

The specific contents of this experimental assessment include the following three parts:

1. Extracting magnesium sulfate from primary salt mud? 7H2O .

2. Determine magnesium sulfate? 7H2O content.

3. Answer the thinking questions and complete the experimental report.

Second, some properties of matter.

1、Ksp？ [Mg(OH)2]= 6.0× 10- 10 Ksp？ [Calcium hydroxide ]=3.7× 10-6

Ksp？ [Fe(OH)3]=3.0× 10-39 Ksp？ [Fe(OH)2]= 8.0× 10- 16

Ksp？ [Mn(OH)2]= 4.0× 10- 14 Ksp？ [Aluminum hydroxide] =1.3x10-33

2. Solubility of substances (g/ 100gH2O)

3. Relative atomic mass: H l.0 1, O 16.00, S 32.07, Mg 24.3 1, Zn 65.39.

Third, the main reagents and instruments

1, reagent

Each experimental table: industrial salt mud (26 grams), 6 mol? L- 1HCl， 1: 1 NH3？ H2O, chrome black T indicator, EDTA standard solution (500ml).

Public experimental table: 6mol? L- 1H2SO4, 25% triethanolamine, NH3-NH4Cl buffer solution (pH= 10), NaClO solution (C.P.), acetone and Zn particles (reference).

2. Tools

(1) glassware

Beaker 1 50ml 1 acid burette 50ml1.

Beaker 250ml 1 volumetric flask 250ml 1

Beaker 400 ml 1 pipette 25 ml 1.

Beaker 1000 ml 1 conical flask 250 ml 3.

Measuring cylinder 50ml 1 weighing bottle l.

Measuring cylinder 1 0ml 1 bottle1

Evaporating dish 200ml 1 rubber pointed dropper 2.

Petri dish 1 set of glass rods 1.

L Buchner funnel and 1 filter bottle in watch glass.

(2) Equipment: gas lamp, tripod, asbestos board, asbestos net, iron frame, butterfly clip, label paper, extensive pH test paper (1~ 14), precise pH test paper (0.5~5.0), filter paper, angle spoon, ear washing ball, protective glasses, gloves, etc.

(3) Common instruments: electronic balance (sensitivity 0.0 1g), analytical balance (sensitivity 0. 1mg) and suction pump.

Fourth, the experimental steps

L. magnesium sulfate? Preparation of 7H2O (30 points)

Add 120 mL of water into a beaker containing 26g of salt mud, stir it into slurry, and drop 6 mol? L- 1 H2SO4 is about 18 mL, and fully stir while dripping to prevent the slurry from overflowing. When it is observed that less gas is generated in the reaction, heating is started, and H2SO4 is continuously added dropwise, and the pH value of the solution is adjusted to 1~2, and heating is carried out for 20 to 30 minutes, so as to keep the volume and pH value of the solution. After the reaction is completed, filter and rinse with a little warm water. Filter residue is discarded; Pour the filtrate into a 250 mL beaker, dropwise add NaClO solution until the pH value of the solution is 5~6, and heat and boil for about 5~ 10 minute to generate dark brown precipitate in the solution. When the volume of the solution is about 80~ 100 mL, immediately filter while it is hot and rinse with a little hot water (if the filtrate turns yellow, NaClO should be added to repeat the above operation). Discard the filter residue, pour the filtrate into an evaporating dish, heat, evaporate and concentrate until it is thin and thick, then turn off the fire, take down the evaporating dish and put it on the asbestos board, cool and filter. Wash the crystal with15ml acetone. Put the washed crystals in a Petri dish and dry them in a fume hood for 30 minutes.

Dry magnesium sulfate? 7H2O products are weighed on the electronic balance, and the product quality is recorded and signed by the invigilator.

2. Magnesium sulfate? Determination of 7H2O content (50 points)

Note: All analytical experiments must be measured in parallel for 3 times, and the original data, calculation results and relative range should be filled in the experimental report, which should be signed by the invigilator.

(1)0.02 mol? Calibration of L- 1 EDTA standard solution

Calculate and calibrate 0.02 mol by yourself? The weighing range of zinc particles in L- 1 EDTA standard solution is written on the experimental report. After being signed by the invigilator, the invigilator will issue relevant experimental instructions (page 6 of the experimental paper), and then the EDTA calibration experiment will be carried out. If you can't calculate, you can directly ask the invigilator for the relevant experimental instructions (page 6 of the experimental questions) to continue the experiment, but you should deduct the calculation points.

(2) magnesium sulfate? Determination of 7H2O content

Accurately weigh magnesium sulfate? Several grams of 7H2O product (calculate the weighing range and write it on the experimental report paper; If you can't calculate, you can directly ask the invigilator for the weighing range, but you should deduct the calculation points. ) in a 250 mL conical flask, add 25 mL deionized water, dissolve it, add 5 mL 25% 25% triethanolamine, shake it well, then add 10mL NH3-NH4Cl buffer solution, shake it well, add chrome black T indicator, the color of the solution is purplish red, and titrate with EDTA standard solution until the solution just turns pure blue. Record the V2 volume consumed by EDTA. Calculate magnesium sulfate with the concentration of EDTA standard solution given to you by the invigilator? 7 H2O content.

Five, thinking (see page 4 of the experimental report) (20 points)

L, when adding H2SO4 to the salt mud for reaction, why should the pH value of the solution be controlled at 1~2?

2. Preparation of magnesium sulfate? 7H2O, the role of adding NaClO.

3. In the preparation experiment, after NaClO is added and boiled, why should it be filtered immediately while it is hot?

4. estimate MgSO4? Theoretical yield of 7H2O.

(page 6 of the experiment)

0.02 mole? Experimental description of calibration of L- 1 EDTA standard solution

Accurately weigh 0.26 ~ 0.39g of zinc particles into a small beaker of 150 mL, cover it with watch glasses, and drop 6 mol along the tip of the beaker? L- 1 HCl 6 mL, when zinc particles are completely dissolved, quantitatively transfer to a 250 mL volumetric flask, dilute to scale with water, and shake well.

Accurately suck 25 mL of the zinc standard solution into a 250 mL conical flask and drop it into 1: 1 NH3? H2O until white precipitate appears, then add 10 mL NH3-NH4Cl buffer solution, shake well, add 20 mL deionized water, add chrome black T indicator, and titrate with EDTA standard solution until the solution just turns pure blue. Record the volume of V 1 consumed by EDTA, and calculate the concentration of EDTA.