In chemical experiments, the role of gas collector cylinders

The gas collector cylinder is a kind of wide-mouth glass container, the bottle mouth is frosted flat, which can maintain close contact with the ground glass and is not easy to leak. It is mainly used to collect gases, assemble gas washing cylinders and carry out reactions between substances and gases.

Precautions for the use of gas collection cylinders:

1. It cannot be heated.

This instrument cannot be heated, it is easy to burst when heated, and if you need to heat it, you need to use a round-bottom flask and beaker.

2. Spread fine sand or water.

When the substance is burned in the gas collection cylinder, the bottom of the cylinder should be spread with fine sand or water to prevent it from bursting. Some substances can only be burned with sand and soil, such as NA, and the splashed NA reacts with water to release hydrogen, which is easy to ignite.

It is used to collect or store a small amount of gas, the combustion of gas, and the combustion of substances in this gas. It is also used to wash gas cylinders, such as adding concentrated sulfuric acid as a drying device.

The bottle mouth is facing upwards: the density of the collected gas is less than that of air (e.g., H2, NH3), the density of the collected gas is greater than that of air (e.g., CO2, O2), and the gas collection cylinder is always short in and long out when it is filled with water.

The bottle mouth is facing down: the density of the collected gas is greater than that of air when it is short in and long out (such as CO2, O2), and the density of the collected gas is less than that of air (such as H2, NH3).

If the device is used for washing gas (such as removing water with concentrated sulfuric acid), it will always be long in and short out.

(Bottle mouth facing up) the long in and short is the washing gas, and the short in and long out is the collection of gas.

Gas Gathering Method.

Drainage gas collection method.

The drainage gas collection method is used to collect gases that are insoluble in water and insoluble in water, such as N2, O2, NO, CO, CH4, C2H2, C2H4, H2, etc.

Upward exhaust air method.

It is used to collect gases that are denser than air and soluble in water, such as Cl2, NO2, SO2, H2S, etc.

Downward exhaust air method.

It is used to collect gases that are less dense than air and soluble in water, such as NH3, H2 and other gases that are fully collected and covered under water. The density is less than air and should be inverted.

If its density is greater than that of the air collector cylinder mouth upward; The density is less than that of the air collection cylinder mouth downward, and the glass sheet slides along the bottle mouth after it is full, so that it cannot enter the water.

1. Drainage method, suitable for gases that are not easily soluble in water. For example, hydrogen, oxygen.

2. Upward air exhaust method, suitable for gases that are denser than air and soluble in water, such as carbon dioxide and chlorine.

3. Downward air exhaust method, suitable for gases that are less dense than air and soluble in water, such as ammonia and hydrogen.

The upward air exhaust method is suitable for gases that are denser than air, while the downward air exhaust method is the opposite.

There is also a drainage method, which is suitable for gases that are not easily soluble in water.

Common: upper and lower exhaust air method, drainage method.

Uncommon: mercury discharge method, upper and lower discharge of noble gas method.

The function of water in the experiment is to measure the volume of O2 by measuring the volume of water entering the water, and it also has the effect of absorbing heat and absorbing white smoke (or preventing the temperature in the bottle from rising rapidly and preventing the generated phosphorus pentoxide solids from polluting the air);

The function of water in b is: to absorb combustion products and prevent sulfur dioxide from polluting the air;

The function of water in C is: to prevent the generated red-hot melt from falling to the bottom of the bottle and rupturing the gas collection cylinder;

Therefore, the answer is: a: the volume of O2 is measured by the volume of water entering the water, and at the same time absorbs heat or absorbs white smoke (or prevents the temperature inside the bottle from rising rapidly, and prevents the generated phosphorus pentoxide solids from polluting the air);

b: Absorb the generated sulfur dioxide gas to prevent sulfur dioxide gas from polluting the air;

c: Prevent the high-temperature melt generated by the reaction from splashing down and bursting the bottom of the bottle (or prevent the splashed melt from bursting the bottom of the gas collection cylinder).

1. All O2, CO2, SO2, etc., A in and B out; Collect H2 etc., B in A Out.

For the device in the picture, it is actually the exhaust air method to collect the gas. This unit is often used to collect gases that need to be treated as off-gases, such as SO2.

If the gas is lighter than air, that is, the relative molecular mass is smaller than the average relative molecular weight of air (29), such as H2, etc., B in and A out should be selected.

The reason is as follows: after the gas enters from B, because the density is smaller than the air, it will float above the air, that is, the mouth of the bottle, and the collected gas will gradually squeeze out the air in the gas collection cylinder from below (that is, the A end), and when the gas occupies the entire gas collection cylinder, the full bottle of gas is collected.

If it enters from A, the incoming gas will float to the mouth of the bottle and go out directly from B, so it will not be able to collect gas.

If the gas is heavier than air, that is, the relative molecular mass is larger than the average relative molecular weight of air (29), such as O2, CO2, etc., A in and B out should be selected.

The reason is as follows: after the gas enters from A, because the density is greater than the air, it will sink below the air, that is, at the bottom of the bottle, and the accumulated gas will gradually squeeze out the air in the gas collection cylinder from above (that is, the B end), and when the gas occupies the entire gas collection cylinder, the full cylinder of gas is collected.

If you enter from B, the incoming gas will sink to the bottom of the bottle and go out directly from A, so it will not be able to collect gas.

A port intake. Oxygen is denser than air and will expel air from the upper mouth.

If the air is inlet from port B, the oxygen will go out from the A and will not be able to collect the gas.

Draw a horizontal line from the bottle, regardless of the square upside down, the gas with a density greater than air is introduced from the lower nozzle below, and the gas with a density smaller than the air is passed from the upper nozzle at the top.

a, this is collected by the exhaust method. If the gas is denser than the air, we imagine it as water, and you think about whether it is a-in. Vice versa. Oxygen is denser than air.

A in B out. This is the case when the density is greater than air, which squeezes out the air inside the bottle and collects gases.