The coefficient of surface tension of a liquid is a value that accurately describes the ability of a liquid to contract and which is measured by the force of surface tension, which affects the unit length of a line located on the surface of a liquid. In the event that the size of the length of the boundary of the liquid surface is denoted by l, and the surface tension of the film, which acts on this boundary, is F, thus, the value of the surface tension coefficient will be:
Ο = F / l
The name of the surface tension coefficient is expressed in N / m. The higher the temperature, the lower the Ο value for pure liquids.
A consequence of the asymmetric forces of the molecular interaction of the transition layer with the molecules surrounding them is the idea of ββthe existence of normal and tangential forces with respect to the interface. These forces have a significant effect on the molecules of the transition layer. They are the forces of molecular pressure and surface tension between the phases.
The dependence of the coefficient Ο on the presence of various impurities
The surface tension coefficient is directly related to the forces of molecular interaction and can take on a wide variety of values ββfor various liquids. For liquids that evaporate very well (alcohol, gasoline, ether), the surface tension is not as high as for liquids that are not volatile. First, we put the grid on the hydrometer, and then lower it into water. Thanks to the dense grid, the hydrometer will be held at a certain depth. Next, drip a little ether onto the grid, after which the hydrometer will immediately rise from the water.
The surface tension coefficient of water is related to how many impurities are in the water. A small sliver of a match is placed on the surface of the water. After that, a bar of soap descends into the water. After a certain period of time, it will be possible to observe the movement of the chips to the edge of the vessel from the soap. As a result of this, we can conclude: the coefficient of surface tension can be reduced with soap. If you add substances that differ in biological activity (paste, soap, washing powders), then the surface tension will be reduced. Then, if you need to get bubbles, why do people add soap?
Many of us believe that due to soap, Ο increases. In fact, it just reduces the surface tension to about one third to the Ο value of pure water. It should be noted that when the soap film is stretched, the concentration of soap molecules on the surface decreases, while the surface tension increases. Therefore, under the influence of soap weak sections of the bubble intensify and do not stretch further. In addition, thanks to soap, water does not evaporate, which means that the life of the bubble increases.
Now let's put this experience: we put sugar candy in water. This will cause the sliver to move toward the candy. The conclusion is clear: under the influence of sugar, the surface tension index increases.
How to determine the coefficient Ο by capillaries?
To carry out this simplest kind of experiment, you need to have several vessels with water and capillaries.
The capillary must be lowered into a vessel with water, and then measure the height of the liquid. Next, another capillary is placed in soapy water, after which the height of the liquid is measured. The coefficient Ο can be found from the corresponding formula:
Ο = Οgdh / 4
Next, you should compare the surface tension coefficients of various types of liquids.