There was no experimental phenomenon of water stop clamp in the chemical oxygen content determinatio

In the experiment of measuring the content of oxygen in the air, attention should be paid to guiding students to observe the experimental phenomena and experience the thinking process of deriving conclusions from experimental facts.

In the experiment, it can be observed that the red phosphorus burns, producing a large amount of white smoke and emitting a large amount of heat; After opening the spring clamp, the water in the beaker enters the gas collector cylinder along the air duct to about 1 5 of the space inside the gas collector cylinder.

Through experiments, it is known that the volume of oxygen in the air accounts for about 1 5.

During the experiment, an excessive amount of red phosphorus should be filled into the combustion spoon, which is enough to make the sealed oxygen in the bell complete the reaction, so that the measured volume of oxygen is closer to the actual volume of oxygen in the air. This experiment also deduces that nitrogen does not support combustion; After the water surface in the gas collection cylinder rises to a certain height, it cannot continue to rise, which can indicate that nitrogen is not easily soluble in water.

After the combustion of red phosphorus, solid phosphorus pentoxide is generated, which makes the pressure of the air in the gas collection cylinder smaller, less than the outside atmospheric pressure. Under the action of the outside atmospheric pressure, the water in the beaker enters the gas collection cylinder.

The conclusion from the experiment is that oxygen is about 1 5 of the total volume of air, and in this experiment why is it that sometimes the volume of gas is reduced by less than 1 5? The reasons for the low results may be: (1) insufficient amount of red phosphorus; (2) The oxygen in the bottle is not depleted; (3) Air leakage of the device (such as the plug is not tightly plugged, there is a gap between the burning spoon and the rubber stopper, etc.), so that the outside air enters the bottle; (4) Open the spring clamp before cooling to room temperature, so that the volume of water entering the bottle is reduced.

In this experiment, sometimes the volume of gas is reduced by more than 1 5, and why? The reasons may be (1) After igniting the red phosphorus, when the burning spoon is inserted, the cork of the bottle is plugged too slowly, which causes the air in the bottle to expand by heat and part of the air to overflow. (2) At the beginning of the experiment, there was no clamp or no clamp on the water stop.

For this experiment, it can be extended as follows.

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There are a large number of bubbles produced at the mouth of the air duct, and the water poured into the bottle after cooling will be much greater than 1 5, and the experiment fails.

After cooling, the water backs up, causing the oxygen content determination experiment to fail.

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!

1) In order to deplete the oxygen in the gas collector cylinder and make the experimental results more accurate, the red phosphorus should be overdosed: the red phosphorus in the gas collector cylinder should be exhausted

2) The phenomenon observed after opening the water stop clamp is: water enters the gas cylinder, and the water entering accounts for about one-fifth of the volume of the gas collector cylinder, indicating that oxygen accounts for about one-fifth of the total volume of air

Therefore, the water enters the gas cylinder, and the water entering accounts for about one-fifth of the volume of the cylinder

A Excessive amount of red phosphorus can ensure that the oxygen in the bottle is completely depleted and meets the requirements;

b If the device leaks, it will cause the volume of water entering to be too small and not meet the requirements;

c Insufficient red phosphorus, resulting in the oxygen in the bottle not being completely exhausted, and the water entering is too small, which does not meet the requirements;

D The device is not cooled to room temperature, resulting in a large air pressure in the bottle, and less water entered, which does not meet the requirements, so choose A

Before the experiment, the water stop clamp should be closed to prevent water from entering and dousing the burning red phosphorus; This results in a measured oxygen volume fraction of less than 1

5 Possible reasons for the results: (1) insufficient amount of red phosphorus; (2) The oxygen in the bottle is not depleted; (3) Air leakage of the device (such as the plug is not tightly plugged, there is a gap between the burning spoon and the rubber stopper, etc.), so that the outside air enters the bottle; (4) Open the spring clamp before cooling to room temperature, so that the volume of water entering the bottle is reduced.

The measured oxygen volume fraction is greater than 1

5. It means that there is more gas coming out of the device, that is, it is possible to stuff the rubber stopper into the bottle mouth too slowly, because the gas in the bottle is driven out due to phosphorus combustion and heat release, or the spring clamp is not clamped during combustion, which causes the gas to expand by heating, and finally enters the liquid more (because the device leaks will cause the liquid to be difficult to enter the device, so it will not lead to more than 1

5), so chosen

So the answer is: close; The amount of red phosphorus is insufficient, and the air tightness is not good; ①

a. When the water stop clamp is opened without cooling to room temperature, the water entering the container will be less than one-fifth of the volume of the container, that is, the volume of oxygen early group is less than 1

This option is incorrect;

b. If the water stop clamp is not clamped during combustion, it will cause the gas in the container to escape outward, resulting in the volume of oxygen greater than 1

This option is correct;

c. The catheter is filled with water first, which does not affect the experimental results, and this option is incorrect;

d. If the combustion spoon is inserted too slowly, due to the high temperature, the gas in the container will expand and escape outward, resulting in the volume of oxygen in the chain balance being greater than that of Lu Zhaoyin1

Therefore, b; d additive: the burning spoon is inserted too slowly

Before the experiment, the water stop clamp should be closed to prevent water from entering and dousing the burning red phosphorus; This results in a measured oxygen volume fraction of less than 1

Possible causes of the result: (1) insufficient amount of red phosphorus; (2) The oxygen in the bottle is not depleted; (3) Air leakage of the device (such as the plug is not tightly plugged, there is a gap between the burning spoon and the rubber stopper, etc.), so that the outside air enters the bottle; (4) Open the spring clamp before cooling to room temperature, so that the volume of water entering the bottle is reduced.

The measured oxygen volume fraction is greater than 1

It shows that there is more gas coming out of the device, that is, it is possible to stuff the rubber stopper into the bottle mouth too slowly, because the gas in the bottle is driven out due to the heat release of phosphorus combustion, or the spring clamp is not clamped during combustion, causing the gas to expand out by heating, and finally enter the liquid more (because the device leaks and it will be difficult for the liquid to enter the device, so it will not lead to more than 1

5), so chosen

So the answer is: close; The amount of red phosphorus is insufficient, and the air tightness is not good; ①