15 points to ask about the air exhaust method of junior high school chemistry

How do you collect the gas?

Depending on the nature of the gas, the drainage method and the air exhaust method can be used!

Taking advantage of the fact that the gas is insoluble in water, the gas can be collected by the drainage method, and the gas can be collected by the upward air method or the downward air exhaust method by using the property that the gas does not react with the air and is denser or less dense than the air! For example, oxygen, which does not react with air and has a slightly greater density than air, can be collected by the upward air exhaust method, while hydrogen does not react with air and has a smaller density than air and is collected by the downward air exhaust method! Formula:

It is the premise that it does not react with the air, if the density is greater than the air, the bottle mouth will be discharged upwards and upwards!

If the density is smaller than the air, the air at the mouth of the bottle is discharged downward, choose up or down, and the conduit extends to the bottom of the gas collection cylinder!

The upward air exhaust method is mostly used for gases with a density greater than the density of the air being discharged!

The downward air exhaust method is mostly used for gases where the density of the exhaust gas is less than the density of the air!

To determine whether a gas is to be collected by the upward or downward exhaust air method, it is best to see whether there are solid non-metallic elements in the chemical formula of the gas to be collected (except for elemental gases, which are less dense than the density of air), and if so, then the density of this gas is greater than that of air (but not absolutely, it is generally like this)!

As long as it is insoluble in water, the gas can be drained and taken by air, and its density is greater than that of air can be used by the upward exhaust air method, and if the density is less than the air, the downward exhaust air method can be used. (Tell you a simple method: as long as its relative molecular mass is greater than 19, use the upward exhaust air extraction method, and less than 19 use the downward exhaust air extraction method).

That's what my chemistry teacher told me secretly

It is related to the density of the gas, generally speaking, the density is greater than the air, we use the upward air discharge method, and the density is smaller than the air adopts the downward air discharge method, through which the unwanted gas is discharged, dense and empty, upward.

Dense small space, downward.

Upward emptying method.

The density of the collected gas is greater than that of air, and it is non-toxic, and does not react with the substances in the air to empty downward.

The collected gas is less dense than air, and it is non-toxic, and does not react with substances in the air to discharge the principle.

It is used to collect gases that are not easily soluble in water.

It does not react with water.

Principles of the Drainage Method.

It is used to collect gases that are not easily soluble in water, do not react with water, and have a lower density than water.

Upward emptying method.

The reaction is carried out using the components of the collected gas that is denser than air and does not box the air.

Downward emptying method.

The density of the gas collected by the use is less than that of air.

And do not box the components in the air react.

Principles of the Drainage Method.

It is used to collect gases that are not easily soluble in water.

It does not react with water.

Upward emptying method.

The density of the gas collected by the use is greater than that of air.

Downward emptying method.

The density of the gas collected by the use is less than that of air.

The gas in the air is discharged upwards using the air method.

If it is lighter than air, use the downward air exhaust method, and if it is insoluble in water, the air extraction method is used to drain the air.

Drainage method: except for some gases that are soluble in water (eg.

Carbon dioxide. Ammonia, etc.), most of the gases are insoluble or insoluble in water and do not react with the gas to discharge the air upward: the gas with a greater density than the air will sink under the air in the gas collection cylinder because of its own gravity is too large, and as the reaction progresses, the gas becomes more and more, and the volume increases, and the air is squeezed out of the gas collection cylinder.

Downward air discharge method: the gas with a density smaller than the air will float or even fly upward because its own gravity is too small and the volume is large, so above the gas collection cylinder, the gravity of the air because of the high density is greater than the gas obtained by the reaction, and it sinks under the gas obtained by the reaction, and as the reaction progresses, the gas becomes more and more, and the volume increases, and the air is squeezed out of the gas collection cylinder.

1. The drainage method is based on the fact that the gas is insoluble in water.

2. According to the upward exhaust air method, the gas sinks and discharges the air according to the density of the gas is greater than the density of the air.

3. According to the downward air exhaust method, the gas rises and the air is discharged according to the density of the gas is less than the density of the air.

A commonly used method of collecting gases. It is also called the drainage collection and trembling method.

The method is to fill the cylinder with water and place it upside down in the sink with the mouth below the liquid level. The gas vent is then placed under the bottle mouth. Until all the water in the bottle is drained, the gas is collected.

The disadvantage is that the collected gas contains a large number of water droplets, which generally need to be dried with a desiccant.

The conditions for gas collection by the drainage method are:

1.Does not react with water.

2.It cannot be dissolved in large quantities in water.

Take, for example, the collection of oxygen.

Fill the cylinder with water, cover it with a glass sheet, place it upside down in the sink, and extend the air duct under the mouth of the cylinder, and when the bubbles enter the cylinder, the chain water is discharged. This is known as the drain gas collection method. When collecting gas, it is not possible to collect air bubbles at the catheter orifice, but to wait for the air in the test tube and in the catheter to be cleared until the air bubbles at the catheter orifice are continuously and evenly released.

Preparation: Fill the gas collection cylinder with water, cover a small part of the mouth of the gas collection cylinder with a ground glass sheet (hair side down), and then move horizontally until it is fully covered, if there are bubbles on the water surface, add water until the bubbles are driven away. Then hold the bottle in one hand and press the glass piece in the other and place it upside down in the sink.

Collect the gas: When the air bubbles at the catheter mouth are evenly discharged by the continuous roller, place the catheter mouth inside (below) the mouth of the gas collector cylinder. With the high ingress of gas coats, the water is gradually discharged.

When the gas collapse bubble escapes from the mouth of the gas collection cylinder, it means that the gas in the cylinder is full.

Pull the gas collector cylinder out of the mouth of the conduit, cover the glass sheet under the water surface, and take it out of the water.

Experimental steps: 1. Fill the gas collection cylinder (or test excavation tube) with water and buckle it upside down in the water tank, use a section of the curved glass conduit to extend into the underwater bottle mouth (test tube mouth), and blow the other end on the water and blow into the bottle until the bottle (tube) is almost completely filled with gas (note: when collecting gas to a part, press the gas collection cylinder by hand to prevent the gas collection cylinder from floating and leaking due to the buoyancy of the water).

2. After the collection, it is observed that there are continuous bubbles bubbling out of the mouth of the bottle (tube), indicating that the collection is full.

If you are using a gas collection cylinder:

Slowly slide the glass sheet from one side of the cylinder to cover the bottle, then turn the cylinder upside down and take out the sink.

4. If you are using a test tube: block the mouth of the test tube with your thumb and take out the test tube.

Principle upward exhaust air method.

It is suitable for the collection of gases with a density much greater than air (29), and the gas with a high density will sink, and the air will be squeezed into the bottle mouth in the bottle, and the air will be discharged; The downward air exhaust method is suitable for gases with a much higher density than air, and the gas with lower density will rise upward, and the air will be squeezed out of the bottle mouth in the upside-down bottle, and the air will be discharged.

It mainly collects macrorock gas with a large difference in density from air, and this method tries not to collect gas that pollutes the air, but NH3 can only be collected by the upward air exhaust method.

H2, CO2, O2, etc. can be collected.

The upward air exhaust method is a gas collection method used to collect gases that are denser than air.

Conditions apply. Gases are denser than air, such as carbon dioxide, nitrogen dioxide, oxygen, etc.

Instrument: gas collection cylinder, coverslip, air tube, some instruments and drugs that are full of gas collection cylinders are placed on the experimental table, and the air collection tube is inserted into the gas collection cylinder upside down, and the gas is collected at the beginning, the gas at the beginning is not pure gas, and it takes a while to collect, when the gas collection cylinder has been collected, take out the air guide tube, and push the glass sheet in translation, until the mouth of the gas collection cylinder is covered.

Note that gases (e.g., O2) with a small difference between their relative molecular weight and the average relative molecular weight of air are generally not used because pure gases are not readily available.

The gas collected by the upward exhaust air method cannot react with any substance in the air in the first place, and the density is greater than that of the air, and it is not enough to meet these two conditions, and the most important thing is that the gas cannot pollute the air.

The bottle mouth is upward is the upward air exhaust method, and the bottle mouth is downward is the downward air exhaust method.

Air stripping is denser than air.

Potassium permanganate produces oxygen, and oxygen can be collected using the drainage method, which should be the reaction you are talking about.

The exhaust method is mainly based on the comparison of the collected gas with the density of the air. If it is denser than air, use the upward air exhaust method, and the smaller air will go downward. It also does not react with the air components. The drainage method is mainly not reactive with water, and it is difficult to dissolve in water.

Fill the cylinder with water and cover it with frosted glass. Then go to the house and pour out the water and cover the frosted glass sheets.

Is it exhaust air or oxygen?