Why is it oxygen that is excreted in the chemical oxygen measurement experiment in the third year of

Because oxygen is a chemically reactive gas, there are many other gases in the air, and if you can get all the other gases out, then you can measure the volume fraction of oxygen, but obviously there is no red phosphorus in the textbook. It consumes only oxygen, less oxygen, so the volume of water replenished can be considered to be the volume of oxygen.

Because red phosphorus combustion consumes only oxygen, the volume of rising water is exactly equal to the volume of oxygen consumed. And this experiment is to prove this. The reason why charcoal and sulfur powder are not used instead of red phosphorus is because burning red phosphorus only consumes oxygen and does not produce other new gases, and the pressure in the bottle basically does not change, so the oxygen volume cannot be measured.

Purely personal opinion, I am a student who has just entered the third year of junior high school, please point out anything wrong Thank you

Because the combustion of red phosphorus consumes oxygen, not discharge, and nitrogen and noble gases are chemically stable and do not participate in the reaction, the volume of water inhaled can be regarded as the volume of water.

Oxygen reacts with red phosphorus, and the white smoke is solid, and then the pressure becomes smaller, and the water enters the gas collection cylinder, and the volume of water entering is equal to the volume of oxygen that is reacted off!

Because red phosphorus consumes oxygen, the volume of rising water is equal to the volume of oxygen consumed. Hope I can help you.

Because oxygen is not easily soluble in water!

Your question is unclear, so it's better to write it clearly!

Summary. This is because red phosphorus reacts with oxygen to produce phosphorus pentoxide.

Because phosphorus pentoxide is solid, it should be a smaller gas.

And because it is derived from the law of conservation of mass, the mass does not change, but the mass of the gas decreases, and the total mass does not change.

Experimental problem for determining the oxygen content in air.

This is because red phosphorus reacts with oxygen to produce phosphorus pentoxide. Because phosphorus pentoxide is solid, it should be a smaller gas. And because it is derived from the law of conservation of mass, the mass does not change, but the mass of the gas decreases, and the total mass does not change.

If the gas is in a closed bottle, if the oxygen is consumed, the remaining gas will fill the whole bottle, and the volume will not change, but the density will decrease (before the spring clamp is opened), and can you tell me what the law of conservation of mass is probably not very understood

The gas is reduced because the solids take up the space.

If you don't understand, just ask: Isn't the decrease in gas because red phosphorus burns oxygen (?)

Uh-huh, yes.

Then what is the effect of the solid space occupied by your previous article on the problem, I don't understand very well, look at the experiment**White smoke is dissolved in water (?) What is the direct relationship between the volume and the density (?) And how to understand the conservation of mass.

The formula for the law of conservation of mass: a+b=c+d. The law of conservation of mass was tested for the last time at the end of the 19th century, when precision measurement technology was already highly developed. The results show that there is no change in mass in any physical reaction.

When measured with red phosphorus, a large amount of white smoke is generated when red phosphorus (which cannot be replaced by charcoal, sulfur, iron wire, etc.) is burned, and the water surface in the bell gradually rises, and after cooling, the water surface rises by about 1 5 volumes. Basically, oxygen accounts for 1 5 of the air. 1. Determination of oxygen content in air

Experimental phenomenon: A large amount of white smoke is generated when red phosphorus (which cannot be replaced by charcoal, sulfur, iron wire, etc.) is burned, and the water surface in the bell gradually rises, and after cooling, the water surface rises by about 1 5 volume. If the measured rise in the water surface is less than 1 5 volumes, the reasons may be:

The red phosphorus is insufficient, the oxygen is not fully consumed, the device is leaking, and the spring clamp is opened before it has cooled to room temperature. 2. The French chemist Lavoisier proposed that air is mainly composed of oxygen and nitrogen. Schoeller and Priestley used different methods to produce oxygen.

3. The composition of air is calculated according to the volume fraction, which is about 78% for nitrogen, 21% for oxygen (nitrogen is about 4 1 for oxygen), and rare gas (mixture) is carbon dioxide, and other gases and impurities. The composition of air is mainly nitrogen and oxygen, which is a mixture. 4. The harmful substances emitted into the atmosphere can be roughly divided into two categories: dust and gas, and the most gaseous pollutants are SO2, CO, and NO2, which mainly come from the combustion of fossil fuels and the exhaust gas of factories.

Abstract:Through learning, we know that the volume percentage of oxygen in the air is about 21%, about 1 5 of air, in order to verify this conclusion, the third chemistry textbook of the upper section of the junior high school uses copper to react with oxygen under heating conditions to do experiments, this experiment uses the properties of oxygen combustion to prove the percentage content of oxygen, but the experimental effect is not ideal, we transform it, and finally can get the above conclusion more obviously.

The specific operation steps of the experiment are as follows: there is 20 ml of air in the closed system composed of two syringes, a section of glass tube is connected between the two syringes, the glass tube equipped with a fine copper wire is heated, and after the temperature of the copper wire rises, the two syringe pistons are slowly pushed alternately, back and forth 5-6 times, the phenomenon is observed, the heating is stopped and cooled to room temperature, the volume of gas in the syringe is read, and the experimental research is carried out in accordance with the above requirements, and the conclusion obtained theoretically should be that oxygen accounts for about 1 of the air volume 5. However, due to various objective reasons, we have done a lot of experiments and have not been able to reach the above conclusions accurately. Through observation, we found that it is possible that too little copper was put in this experiment, the oxygen reaction was not completed, and the phenomenon after the reaction was completed was not obvious, which hindered the reading of the data.

So we came up with the idea of improving this experiment, using the combustible properties of oxygen, red copper is burned in oxygen to form black copper oxide, after the full reaction, because the oxygen is consumed, so the pressure in the closed system is smaller than the outside atmosphere, the outside atmosphere pressure will press the piston in, the difference between the reading at this time and the reading before the reaction is the amount of oxygen that is reacted. It can be seen that the magnitude of the pressure plays a very important role in this experiment, and it is the small change of the pressure that is used to complete this experiment.

Improvement: Replace copper with red phosphorus, use certain substances (such as phosphorus) to react with oxygen in the air (no gas, form solids), reduce the pressure in the container, and let water enter the container. The volume of water entering the container is determined, i.e. the volume of oxygen in the air.

Determination of oxygen content in air.

The combustion of red phosphorus consumes oxygen and produces solid phosphorus pentoxide, because the oxygen is gone, and the internal air pressure is less than the external air pressure (which we have not yet learned in physics), so the water is sucked into the gas collector cylinder to 1 5, so that the oxygen content in the air is measured to be about 1 5

[Experimental Procedure].

Connect the device and check the airtightness of the device.

Light the red inside the incendiary spoon.

Inner phosphorus, immediately.

Reach into the gas collector cylinder and plug the stopper tightly.

Once the red phosphorus is extinguished and cooled, open the spring clip.

Experimental phenomenon】 Red phosphorus burns, producing a large amount of white smoke; Exothermic; After cooling, the spring clamp is opened, and the water enters the gas cylinder along the conduit, and the volume of water entering the gas cylinder accounts for about 1 5 of the total volume of air in the gas cylinder.

The above is the detailed steps and phenomena, if you still need experimental conclusions and precautions, please ask me

1. Experimental phenomena.

1) The bell jar is filled with white smoke; (2) After a while, the white smoke disappeared, and the water level inside the bell rose to about 1 5

2. Precautions for experiments.

1) The substances that can be used for the reaction must be substances that are easy to react with oxygen and have no gas formation (such as red phosphorus), and charcoal and sulfur cannot be used as reactants for determining oxygen content.

2) If the liquid used is not water, but alkaline solution (such as NaOH solution), it is theoretically feasible to use carbon and sulfur as reactants, because the generated gases CO2 and SO2 can react with NaOH solution and be absorbed.

3) The substance used for the reaction must be sufficient or excessive.

4) The airtightness of the container must be good.

5) The volume of water entering the container should be measured only when it has been cooled to room temperature, otherwise the volume of the water rising in the bell jar is less than 1 5

1. Determination of oxygen content in the air: Experimental phenomenon: Red phosphorus (can not be replaced by charcoal, sulfur, wire, etc.) has a large amount of white smoke when burning, and at the same time, the water surface in the bell gradually rises, and after cooling, the water surface rises by about 1 5 volume.

It seems that you can cut out the examples.

Personal insights! )

With H2S aqueous solution (i.e., hydrosulfuric acid): a colorless gas is introduced into hydrosulfuric acid, if a yellow precipitate (sulfur element) is produced, and after complete precipitation, the supernatant is taken and dilute nitric acid acidified silver nitrate solution is added dropwise, if there is no precipitation generated, it proves that the colorless gas introduced is oxygen.

Or test with BA(HSO3)2 solution, if a colorless gas produces a white precipitate after passing into the solution, it proves that the gas is oxygen:

2hso3-o22h+

2SO42- (bisulfite ions are highly reducible and are immediately oxidized by O2); ba2+ so42-

BaSO4 (the resulting SO42- precipitates with barium ions to form BaSO4).

I seem to remember an organic reagent, the name is not clear. However, this is a test for the very small amount of oxygen dissolved in the liquid.

Generally, after collecting gas with a gas collection cylinder, it can be tested with a Martian wooden strip.

1.Plugging in too slowly and not clamping the spring clamp can cause air to enter the cylinder, which is counted as oxygen.

2.The device leaked, and the oxygen in the bottle escaped into the air.

3.If it is not cooled, oxygen will escape if the pressure inside the bottle is strong, and the result is small.

Happy New Year!

1. If the rubber stopper is stuffed too slowly and the spring clamp is not clamped, part of the air will be released into the air during dry heating, resulting in an increase in the reduced gas in the bottle, and the amount of water refluxed at the end of the experiment will increase, resulting in a result greater than one-fifth.

2. If the device leaks, the gas outside the bottle will also enter the bottle from the leakage place when the water is returned, so that the amount of water entering the bottle will be reduced, resulting in less than one-fifth of the result.

3. The experimental data can be accurate at room temperature before the experiment and room temperature after the experiment.

1.Air enters the bottle and the amount of oxygen increases 2Oxygen leakage in the bottle 3Cooling the room temperature is to prevent the gas from expanding.

There are two reasons why the experimental results are greater than 1 5

First, the cork of the bottle is not quickly tightened after igniting the red phosphorus, resulting in the gas in the bottle expanding due to heat and escaping from the mouth of the gas collection cylinder.

The second is that the spring clamp is not tightened, and the gas temperature in the bottle rises and expands when the red phosphorus is burned, and a part of the gas will escape from the catheter.

This theoretically cannot be 2 5 of the volume of air, there may be two kinds: there is water inside the reagent bottle before the reaction, which you calculate as part of the water level ** that sucks after the reaction; Another possibility is airtightness. Since you said that the air tightness is good, then such an obvious error must be the first error of experimental operation.

Therefore, the most effective way to prove this is to repeat the test, and the conclusion will be verified naturally.

It's possible that the gas expands when it is heated and you put it in the water before it cools, so that some of the water is produced by the expansion of the gas.

Is it included a small amount of water that is added to the gas collection cylinder before burning? Generally speaking, the water in this experiment is less than one-fifth, and it is difficult to achieve one-fifth.

It's possible that you didn't wait until the cylinder was completely cooled before opening the water stop, so the air inside the cylinder was heated and expanded! It's also possible that your spring clips aren't tightened!