Chemistry competition questions in the third year of junior high school, eager for answers!!

1) because new impurities NO3 2- will be introduced;

2) Remove a small amount of the solution after step 1 into a clean test tube, drop a few drops of H2SO4 dilute solution, if there is a white precipitate generated, that is, BaCl2 has been excessive;

3) removal of Ca2+ and excess Ba2+;

4) Beakers, glass rods, evaporation dishes, funnels, iron frames, alcohol lamps, rubber head droppers, filter paper;

5) Filtration operation: the filter paper should be close to the funnel wall; Place the glass rod against one side of the three-layer filter paper; The filtrate is slowly drained with a glass rod; The bottom of the funnel is against the wall of the beaker.

Evaporation operation: the evaporation solution should not be more than 2 3 of the volume of the evaporation dish, stir with a glass rod during evaporation to prevent boiling; When a crystalline film appears, immediately stop heating and evaporate dry with residual temperature.

1) What is the reason why BACL2 in step cannot be changed to BA(NO3)2?

A: No, you cannot. Because it will bring in NO3- (impurities).

2) After the steps, how can I tell if there is an excess of BACL2?

Answer: Let it stand, add BaCl2 solution dropwise in the supernatant, if there is no turbidity, it means that BaCl2 has been excessive, otherwise you need to continue to add dropwise.

3) What is the purpose of joining NA2CO3?

Answer: Remove Ca2+, Ba2+ ions in solution.

4) What are the main instruments that need to be used in the above operations of coarse salt purification?

Answer: Medicine spoons, beakers, glass rods, funnels, filter paper, iron racks, iron rings, evaporation dishes, alcohol lamps.

5) The experimental protocol needs to be improved, please write out the specific operation steps.

The steps are almost complete, and I don't think there is any need to add any more steps. What is lacking should be how to judge whether the added impurity removal reagent is sufficient and the problem of precautions in filtration and evaporation.

1) Because this is a misunderstanding of purification, excess ions cannot be added, resulting in unnecessary separation processes.

2) Extract a small amount of the solution after step 1, and then add a small amount of the original crude salt solution, if there is a sedimentation generation, it means that there is an excess, if not, the opposite.

3) The calcium ions in the filtered solution are settled to achieve the purpose of removing Ca ions.

4) Beakers, test tubes, droppers, glass rods, filters, alcohol lamps.

5) Do not purify and filter, otherwise the refined salt will not be pure.

1) Because nitrate impurity ions will be introduced.

2) No more white precipitates.

3) Remove calcium ions and excess barium ions.

4) It is mainly a three-step operation of dissolution, filtration and evaporation. The main instruments are beakers, glass rods, funnels, filter papers, iron frames, evaporation dishes, alcohol lamps, etc.

5) When adding three excess reagents, it is best to filter them gradually.

1. Nitrate cannot be removed.

2. Add sulfuric acid.

3. Remove barium ions and calcium ions.

4. Beakers, funnels, glass rods, iron frames, crucibles, alcohol lamps. 5，

1.Bring in new impurities.

2.No more precipitation generation.

3.Precipitate calcium and barium ions.

4.Droppers, filter beakers, glass rods, funnels, filter paper, iron racks, iron rings, evaporation dishes, alcohol lamps.

5.Heating process.

1.Nitrate ions will be introduced; 2.Take the upper layer overnight, continue to add BACL2 dropwise, and see if there is a precipitation; 3. Remove calcium and barium ions in solution; 4.

Glass rods, funnels, beakers, iron stands (with iron rings), crucibles 5Step 6, appropriate amount of dilute hydrochloric acid, and compare with pH test paper until neutral.

This is a simple question, one is that there is not enough CO2, and only CaCO3 is generated

co2 --caco3

x x = There is also an excess of CO2, which generates part of Ca(HCO3)2 and CaCO3

So first CO2 reacts with all Ca(OH)2, and then excess CO2 reacts with CaCO3.

co2---ca（oh）2 --caco3

x y x= y=1g now there is a precipitate for, then dissolved so.

co2---caco3 --2ca(hco3)2

z z= so total consumption.

The answer is c

If the ratio of the number of cations is Cu2+:K+=3:4, then we can set the number of Cu2+ as 3 and the number of K+ as 4, then the sum of the number of charges carried by the cations is (+2)*3+(+1)*4=+10

The solution is electrically neutral, so the total number of charges carried by the anion is also 10, so that the number of SO2- is x, and the number of CI- is y

then (-2)*x+(-1)*y=-10

Solution: 2x+y=10

Substituting the four answers of ABCD, only C is true.

So the answer is c

Let's look at the possible combinations of CuCl2 CuSo4 Kcl K2SO4, then if they are all Cu combinations, SO4:Cl=

3：6=1:2。In the same way, if K is combined with SO4 and CL, the ratio is 1:1, and these two values are extreme hypothetical values, so the answer is between 1, and the answer is D, I don't know if it's right, but can it help

First, calculate the mass fraction of the CL element in NaCl:

Then calculate the mass fraction of NaCl in seawater:

Learn mathematics, physics and chemistry well, and learn to dazzle the world.

ch4+h2o=co+3h2

From this reaction, we can see that if there is only CO and H2, then the production of a CO molecule corresponds to the production of 3 hydrogen molecules, and then there is a carbon atom in a CO molecule, and the total relative mass of the carbon element is 12; There are 6 hydrogen atoms in 3 hydrogen molecules, and the relative mass of the total hydrogen element is 6*1=12, so the mass ratio of carbon to hydrogen is 2:1

If there is only CH4, then both carbon and hydrogen are from CH4, and it can be seen from the molecule CH4 that one carbon atom corresponds to 4 hydrogen atoms, so the mass ratio of carbon to hydrogen is 12*1:4*1=3:1

Do you just want to know these 2 ratios?

1)ch4+h2o=co+3h2

2)i．14：3

Refine the experimental design] Conduct the experiment] Red.

Phenomenological analysis and data processing].

If only CO and H. Reducing sufficient CuO, the ratio of the number of molecules of CO to H2 in the syngas is 1:3. The mass ratio of carbon to hydrogen in the product is 2; 1

If only CH4 reduces a sufficient amount of CuO, the mass ratio of carbon to hydrogen element in the product is 3:1

The mass of CO2 is measured: 201 5g - 198 2g = 3 3g H20 mass: 896 0g - 292 4g = 3 6g

The mass ratio of carbon element cord to hydrogen element cord in the product is (3·3g)3 6g)9:4

9；4 is between 2:1 and 3:1.

It can be inferred that, in addition to CO and H2, there may be CH4 in the syngas produced to react.

CH4 also restores cuo. (Reasonable process is evenly scored).

Not. Since the removal of water vapor will cause the measured CO2 mass to be low, and the mass ratio of carbon to hydrogen in the actual product is greater than 2:1, it has no effect on the estimated results. (Points are given for reasonable descriptions).

Expand**] clarified lime water hgfi

Experimental reflection] Because the mass ratio of carbon and oxygen in the product is too high to 2:1 according to the measured data, it may be that the ratio of the number of molecules of CO to H2 participating in the reaction in the syngas is greater than 1:3 (or H2 does not fully participate in the reaction

Choosing c is a simple method, and you can set the molecular expression of the gas mixture to cox, where the value of the small foot mark x is between one and two.

44－（12＋16x））／12＋16x）＝32％

Then you can calculate x 4 3, and then you can easily analyze the result yourself (write the mixed molecular formula as 2CO+CO).

Select C Co+Cu==Co2+Cu C:12 O:16 Co:28 Co2:44

The increase in gas mass is due to the conversion of CO to CO2, and 1 unit of CO2 is produced for each unit of CO oxidized to obtain 1 unit of O

It can be seen that before the reaction, CO accounts for 32% 16 28=56%, and CO2 accounts for 44%, so CO:CO2=56% 44%=14:11

Solution: Since the copper oxide is sufficient, then the CO reacts completely, and the amount of the substance of CO is Xmol, and the amount of the substance of CO2 is ymol.

co+cuo=cu+co2 co2

Relationship 1 1

The amount of the substance x x y

Quality 28x 44x 44y

It can be seen that the increased mass is 44x

According to the meaning of the question: 44x (28x+44y)=, find x y=? And then according to the mass ratio 28x 44y=? Find the result.

I don't know if it's right, can you read it? Hehe.

Carbon dioxide is 44 32, all of which are obtained by CO, so the original mass fraction of CO is 32 16 * 28 = 56%, so it is 56:44 = 14:11