How is the waste method used to collect gas? What is the gist of the operation?

Substances that can react with water and substances that are easily soluble in water cannot be collected by drainage.

For example: Cl2, CO2, H2S, SO2, NH3, HCL, NO2, etc.

Gases whose molecular weight is close to the average molecular weight of air (29) and can be soluble in water or react with water cannot be collected by air exhaust and drainage, such as hydrogen sulfide, ethylborane (B2H6), hydrogen silicide (SiH4), and hydrogen cyanide mentioned above.

In addition to the drainage method and the air exhaust method for gas collection, it is possible to collect gas by the liquid drain method. Hydrogen sulfide can be collected with a saturated sodium hydrosulfide solution (hydrogen sulfide has little solubility in a saturated sodium hydrosulfide solution), and chlorine can be collected with a saturated sodium chloride solution in addition to the upward air exhaust method.

The drain method collects a bottle of exhaled air.

A common method of collecting gases. It is also called the drainage gas collection 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 the water will be discharged when the bubbles enter the cylinder. 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 the catheter to be cleared until the air bubbles at the catheter orifice are continuously and evenly discharged.

Procedure.

1.Take the exhaled air of the collector as an example: 1. Fill the gas collection bottle (or test tube) with water and buckle it upside down in the sink, use a section of the curved glass conduit to reach into the mouth of the bottle under the water (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 a part of the gas, press the gas collector cylinder with your hand to prevent the gas collector cylinder from floating and leaking due to the buoyancy of the water).

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

3. If you use a gas collection cylinder:

Slowly slide a glass piece through a section of the cylinder and cover the bottle, 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.

2.Take, for example, the collection of air: fill the cylinder with water, quickly and consistently pour it out and immediately cover the mouth of the bottle with a glass sheet. In this way, a bottle of air is collected.

Advantages and disadvantages:

The drainage gas collection method is a conventional method for collecting gas in the laboratory, which has the advantages of high purity, sufficient collection, no fullness, less waste, and less pollution than the exhaust air method. However, this method also has the disadvantages of limited gas that can be collected (gases that can be dissolved in water cannot be collected), large gas water content, and inconvenient operation.

For example, carbon dioxide can react with water to form carbonic acid, and carbon dioxide is a gas that dissolves in water, so it cannot be collected by drainage.

Gases that can be collected by the drainage method are insoluble in water.

The drainage method, i.e., the method of collecting gases by drainage, is a method of collecting gases in experimental chemistry. This method is used when the gas does not react with water and is not easily soluble in water.

1. The operation method is as follows:

Fill the gas collection bottle with water, cover the mouth with a glass sheet, and then stand upside down in the sink. When there are bubbles at the mouth of the conduit continuously and evenly released, then the conduit mouth is extended into the gas collection cylinder filled with water, when you see air bubbles emerging from the outer edge of the gas collection cylinder mouth, the liquid level in the gas collection cylinder drops to the mouth of the bottle (that is, after collecting a full bottle of gas), cover the bottle mouth with a glass sheet in the water, and move the gas collection cylinder out of the water surface, and put it on the table or upside down

When the collected gas is denser than air, it is being placed on the table.

When the density of the collected gas is smaller than that of air, place it upside down on the table.

2. Precautions:

1. Fill the gas collection bottle with water, without bubbles (you can gently slide the glass piece from one side of the bottle mouth until the bottle mouth is completely covered when keeping the water hose in the state of filling water from the water hose).

2. When stopping collection, the conduit should be pulled out or the sink should be removed before the lamp can be removed to avoid sucking.

3. The exhaust air collection method is suitable for gases with large differences between specific gravity and air, such as H2, NH3, CO2, HCl, Cl2, SO2, O2, etc. Lighter-than-air gases are discharged from the mouth of the bottle using the downward air method, and heavier-than-air gases are discharged from the mouth of the bottle using the upward air method.

Take collecting exhaled air from a person as an example, the operation steps:

1. Fill the gas collection bottle with water and buckle it upside down in the sink, use a section of the curved glass conduit to reach into the mouth of the bottle, and the other end is missing in the water and blow into the bottle until the bottle is almost completely filled with gas;

2. After the collection, it is observed that there are continuous bubbles emerging from the mouth of the bottle, indicating that the gas is fully collected;

3. Slowly slide through a section of the gas collection bottle with a glass piece and cover the bottle mouth, then turn the gas collection bottle upside down and take out the sink.