First, the hand holding method
Experimental operation: immerse one end of the catheter in water and hold the outer wall of the test tube tightly with your hands. If bubbles emerge from the mouth of the catheter and a stable water column is formed in the catheter after releasing the hand, the air tightness is good;
Experimental analysis: when holding a test tube by hand, the air in the test tube expands when heated, and its volume becomes larger. When water overflows from the catheter into the beaker, bubbles can be observed at the mouth of the catheter. When you release your hand, the air temperature in the test tube drops, and the pressure of the gas in the test tube is less than the external atmospheric pressure, so the water in the beaker is pressed into the catheter to form a stable water column.
Second, the liquid sealing method
Experimental operation: immerse the lower end of the long-necked funnel in water, inject water into the long-necked funnel, and then check it by hand; Put the bottom of the long-necked funnel into a water-liquid seal to prevent gas from escaping along the bottom of the long-necked funnel;
Experimental analysis: when holding a test tube by hand, the air in the test tube expands when heated, and its volume becomes larger. When water overflows from the catheter into the beaker, bubbles can be observed at the mouth of the catheter. When you release your hand, the air temperature in the test tube drops, and the pressure of the gas in the test tube is less than the external atmospheric pressure, so the water in the beaker is pressed into the catheter to form a stable water column.
Third, the liquid injection method
Experimental operation: the rubber tube is clamped with a spring, and water is injected into the long-necked funnel, so that the lower end of the long-necked funnel is submerged by water, and the liquid level in the long-necked funnel is higher than that in the conical bottle. After a period of time, the liquid level in the long-necked funnel does not drop, which proves that the air tightness is good.
Experimental analysis: after clamping the spring clip and sealing the lower end of the long-necked funnel, the conical bottle forms a sealed environment, and the liquid level in the long-necked funnel will not drop.
First, the idea of equipment air tightness inspection
The inspected equipment is installed in a sealed system. Through some methods, such as changing the temperature, adding water to the system, or introducing gas, changing the pressure in the system to make the pressure inside and outside the system different, and then observing the phenomenon to judge whether the system is sealed.
Second, where is the equipment easy to leak?
In the experimental device, there are joints between reaction devices (test tube, conical flask, round bottom flask, etc.). ) and rubber plug, the joint between rubber plug and catheter, the joint between catheter and rubber tube, and other positions are usually airtight. In the experiment, it is also important to check these positions when the air tightness of the equipment is not good.