How to use pressure to draw a liquid into a capillary

Note that the previous statement is not true, and plants absorb water from the soil for use"Hair sucking phenomenon"Don't get confused with the water that transports water to the 100-meter-high canopy! The siphon phenomenon we see daily is realized by the equal atmospheric pressure of the liquid surface on both sides of the communicator, when the liquid level on both sides of the communicator is not equal when the atmospheric pressure is not equal, then under the action of atmospheric pressure, the liquid will flow from one side to the other side until the atmospheric pressure on both sides of the liquid surface is equal. In fact, siphoning is not entirely caused by atmospheric pressure, and siphoning can occur in a vacuum.

The force that makes the liquid rise is the cohesive force of the molecules between the liquids. In the event of siphoning, the liquid will continue to flow in one direction because more liquid flows out of the tube than into the tube, and the gravity on both sides is unbalanced. As the liquid flows into the tube, the higher it goes, the lower the pressure.

If the liquid rises from a very high tube, the pressure will be reduced to such a point that bubbles (made up of air or other gases) will be formed in the tube, and the height of the siphon will be determined by the formation of bubbles. Because the bubbles disconnect the liquid, the force between the gas molecules at both ends of the bubble is reduced to 0, thus destroying the siphon effect, so the tube must be filled with water. At normal atmospheric pressure, the siphon works better than in a vacuum, because the atmospheric pressure on both nozzles increases the pressure inside the entire siphon.

1. Reduce the air pressure at the other end of the capillary aspiration, and the liquid will be inhaled under the action of the air pressure difference. 2. When the pressure is increased at the suction end of the capillary, the liquid will also be inhaled under the action of air pressure difference.

1. Measurement method.

There are two methods for determining the surface tension of liquids: static method and dynamic method.

Static method, including capillary rising method, dunouy hanging ring method, Wilhelmy disc method, rotary drop method, hanging drop method, drop volume method, maximum bubble pressure method; The dynamic methods include the shouting state envy spinning drip method, the ** jet method and the hanging drop method. Among them, the capillary rise method and the maximum bubble pressure method cannot be used to measure the liquid-liquid interface tension. The Wilhelmy disc method, the maximum bubble pressure method, and the oscillating jet method can be used to determine the dynamic surface tension.

The surface tension is determined by the static method.

1. Drip weight method.

The drip weight method, also known as the drop volume method, is more accurate and simple. The basic principle is that when a liquid is dropped from a capillary dripper, the size of the droplet is related to the surface tension of the liquid, that is, the greater the surface tension, the larger the droplet, and there is a relationship between the two

w=2πrγf (1)

w/(2πrf} (2)

where w is the weight of the droplet;

r is the radius of the dripper of the capillary, and the magnitude of its value is determined by the measuring instrument;

f is the correction factor. In general, it is more convenient to determine the droplet volume in the laboratory, so Eq. (2) can be written as:

vρg/r)×(1/2πf) (3)

where v is the droplet volume; is the density of the liquid; f is the correction factor.

For a specific measuring instrument and the liquid to be measured, r and are fixed, and the surface tension of the liquid can be calculated by measuring the volume of a few drops of liquid during the measurement process.

2. Capillary ascending method.

A capillary is inserted into the liquid, and the liquid will rise along the capillary, and after it rises to a certain height, the liquid inside and outside the capillary will reach an equilibrium state, and the liquid will no longer rise. At this point, the upward pulling force exerted by the liquid surface on the liquid is equal to the total downward force of the liquid. Rule.

1/2 ρl−ρg ghrcosθ (1)

where is the surface tension; r is the radius of the capillary; h is the height of the liquid level rise in the capillary; l is to measure the density of the liquid; g is the density of the gas (air and vapor; g is the acceleration of the local gravity; is the contact angle between the liquid and the pipe wall. If the capillary diameter is small and =0, then Eq. (1) above can be simplified to .

12ρghr (2)

a. In the capillary with a thin pipe diameter, the liquid is in contact with the surrounding pipe wall, and the force needs to lift this layer of liquid, if the pipe diameter is larger, the area of this layer of liquid is also larger, and the gravity is also larger, and it is not easy to lift, so a is correct;

B, the density of the liquid in a certain volume is smaller, easy to be lifted, so B wrong, C correct, D, and C about the same, because the density of alcohol is smaller than water, so that the density of the mixed liquid decreases, easy to lift so D error;

So choose AC