Коэффициент поверхностного натяжения жидкости – this is a value that accurately characterizes the ability of a liquid to reduce and which is measured by the surface tension force, which affects the unit length of the line located on the surface of the liquid. In that case, if the size of the length of the boundary of the surface of the liquid will be denoted as l, and the surface tension force of the film, which acts on this boundary, is F, thus, the value of the surface tension coefficient will be:
σ = F / l
The name of the surface tension coefficient is expressed in N / m. The higher the temperature, the lower the σ value for pure liquids.
The consequence of the asymmetry of molecular forcesThe interaction of the transition layer with the molecules that surround them is the idea of the existence of normal and tangential forces with respect to the interface. These forces have a significant effect on the transition layer molecules. They are the forces of molecular pressure and surface tension between the phases.
The dependence of the coefficient σ on the presence of different impurities
Surface tension coefficient directlyassociated with the forces of molecular interaction and can take a variety of values for different liquids. For liquids that evaporate very well (alcohol, gasoline, ether), the surface tension is not as high as for non-volatile liquids. At first we put on the grid on the hydrometer, and then lower it into the water. Due to the dense grid, the hydrometer will be kept at a certain depth. Then you should drop some ether into the net, after which the hydrometer will immediately rise from the water.
Коэффициент поверхностного натяжения воды связан with how much impurities are in the water. A small splinter from a match is placed on the surface of the water. After that, a piece of soap comes down to the water. After a certain period of time, it will be possible to observe the movement of the splinters to the edge of the vessel from the soap. As a result, we can conclude: the coefficient of surface tension can be reduced with soap. If you add substances that differ in biological activity (paste, soap, laundry detergents), then the surface tension will be reduced. Then if you want to get bubbles, why do people add soap?
Многие из нас полагают, что благодаря мылу the indicator σ increases. In fact, it just reduces the surface tension to approximately one third to the σ value of pure water. It should be noted that when a soap film is stretched, the concentration of soap molecules on the surface decreases, and the surface tension increases. Consequently, under the influence of soap, weak areas of the bubble strengthen and do not stretch further. In addition, thanks to the soap, the water does not evaporate, which means that the life of the bubble increases.
Now let's put this experience:put the sugar candy in the water. This will cause the sliver to move to the candy. The conclusion is unambiguous: under the influence of sugar, the indicator of surface tension increases.
How to determine the coefficient σ by capillaries?
For the implementation of this simplest of its kind experience you need to have several vessels with water and capillaries.
The capillary is required to be immersed in a vessel with water, andthen measure the lifting height of the fluid. Next, another capillary is placed in soapy water, after which the height of the liquid lift is measured. The coefficient σ can be found from the corresponding formula:
σ = ρgdh / 4
Next, you should compare the surface tension coefficients of various types of liquids.
