How to test the air tightness of different devices in high school chemistry?

There are three methods to test air tightness in high school chemistry: heating method, inflation or pumping method, and water injection method;

Heating method: by increasing the temperature to increase the internal pressure, operation steps and judgment methods, immerse the catheter outlet in water and seal, use the palm to close to the outer wall of the volume, if there is a bubble at the catheter mouth, remove the palm, and the water at the end of the catheter rises to form a stable water column, which proves that the device does not leak; Inflation or pumping method: by increasing or decreasing the amount of gas in the device to increase or decrease the pressure, operation steps and judgment methods, the long neck funnel adds a certain amount of water to the test tube, so that the lower end is immersed in water, a syringe is connected to the catheter, when the piston is pulled out, if there is a bubble at the end of the funnel, or when the piston pushes in, the liquid level at the end of the funnel rises, which proves that the air tightness is good; Water Injection Method:

By injecting water to reduce the volume of gas and increase the pressure, operation steps and judgment methods, close the spring clamp, add water from the long neck funnel to the lower end of the funnel, continue to add water to make the liquid level in the funnel higher than the liquid level in the test tube, if the liquid level is stable and does not change after stationing, the phenomenon proves that the air tightness is good.

There are three main ways to check the airtightness of the device:

1.Hand grip.

This method is appropriate for gas generators with small volumes (e.g., test tubes) and no separating funnel (or long-neck funnel). For example, the air tightness inspection of the equipment for producing O2, NH3, CH4 and other gases in the laboratory.

The specific operation method is: immerse the outlet of the catheter in water, hold the test tube with your hand, if there are air bubbles escaping from the catheter mouth, after letting go of your hand, a small amount of water enters the catheter, indicating that the device does not leak.

2.Alcohol lamp microthermal method.

This method should be used for devices with large container volume (such as round-bottom flasks) where the gas generating device is not directly connected to the atmosphere. For example, the laboratory is prepared to check the air tightness of CH4, SO2, O2, NH3, CH4, C2H4 and other gases. Here's how:

Immerse the outlet of the catheter in water, and use the alcohol lamp flame to heat the bottom of the gas generating device (test tube, round-bottom flask) slightly, so that the temperature in the tube (or bottle) rises slightly, and there are bubbles escaping from the mouth of the tube.

3.Water Injection Method:

This method should be used for devices where the gas generating device is directly connected to the atmosphere or cannot be heated. For example, the laboratory uses Qipu generator to produce CO2, H2, H2S and other gases and the air tightness inspection of the 28th question of the 2001 National College Entrance Examination Science Comprehensive.

The specific operation method is: plug the rubber stopper, inject a certain amount of water from the funnel, make the water level in the funnel higher than the water surface in the container, immediately tighten the piston (or clamp the spring clamp), stop adding water for a period of time, if the liquid level difference between the funnel and the container remains unchanged, indicating that the device does not leak; Plug the rubber stopper, clamp the spring clamp, and fill the test tube with water from the funnel, if the water only stays in the funnel and cannot enter the test tube, it means that the device does not leak.

Three. Illustrate. 1.For large volumes of gas generators (such as round-bottom flasks) or when the room temperature is close to the temperature of the palm, it is better to use the alcohol lamp microthermal method to check the air tightness of the device.

2.If the gas does not need to be heated, it is not necessary to check the air tightness of the device by the alcohol lamp microthermal method.

3.If the gas generator is directly connected to the atmosphere, the airtightness of the device cannot be checked by hand holding or alcohol lamp microthermy.

1. Press the catheter firmly and there are air bubbles.

It is to squeeze out the air, and air bubbles will emerge from the bottom of the catheter (most of the air is O2, N2, insoluble in water), and if the air tightness is not good, there will be no bubbles or very small and sparse.

2. Open the piston slightly, and then open the spring clamp with air bubbles.

The spring clamp clamped the catheter and the air could not get out. When you open the piston of the separating funnel, the water drips, the air volume in the flask is compressed and reduced (just like squeezing the bus, especially in Beijing), the air volume becomes larger again when you open the spring clamp (it is squeezed out), and then it will bubble as above, and the air tightness is not good as above, the principle is that the atmospheric pressure is strong, and the pressure inside becomes smaller after dripping, and the spring clamp becomes larger when you open it.

3. Clamp the spring clamp and fill the long neck funnel with water until the liquid level no longer drops.

The bottom of the long neck funnel is sealed by liquid, but there is air above the liquid in the Erlenmeyer flask, there will be a downward pressure, fill the long neck with water, the water will be pressed into a part by the air pressure above the long neck funnel and its own gravity, and then because the air pressure inside the bottle is slightly greater than the outside of the bottle, the liquid will be pressed upwards to support a section of water column. Since there is also air pressure outside the bottle, the liquid level is stationary at the funnel. If it's not good, it's embarrassing.

4. After closing the spring clamp, fill the non-plugged tube with water, and find that the liquid level of the non-plugged tube is higher than the plugged tube, and shake it twice to find that it remains the same, indicating that the air tightness is good.

Because the air pressure of the plugged tube will become larger after you add water, and the air pressure above the plugged tube is smaller than that of the plugged tube, and the air pressure in the plugged tube can still support the plugged tube after you add water, so the liquid level of the plugged tube will be higher than that of the plugged tube. This uses the knowledge of atmospheric pressure and the communicator, the communicator will be horizontal because the air pressure of the two nozzles is equal, and it will press the water surface to the same height, and when the air pressure of the plugged pipe is compressed because of the incoming water, it will not appear. If the air tightness is not good, how you add it is flat, except for the plug of course =.

., the water in the left pipe will still leak out.

5 ask for an assist, 300 exp for a difference, thank you.

How to check the airtightness of the device is told by experiments, I hope it will help you, come in and take a look.