Factors affecting surface tension

In summary, the surface tension of a substance is indirectly proportional to temperature and is affected by the addition of impurities. The presence of soluble impurities can increase the surface tension, while sparingly soluble impurities can decrease it. This is due to the molecules on the surface experiencing a net downward force, causing it to act like a stretched membrane. This effect can also be seen with the addition of alcohols, as larger-molecule alcohols with both polar and nonpolar ends can decrease surface tension more effectively. However, there is no general rule for predicting the effect of an impurity's solubility on surface tension. Additionally, it is typical for surface tension to decrease as temperature increases."
  • #1
Kaushik
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I read the following two points:
  • Temperature is indirectly proportional to surface tension.
  • Adding impurities affect the surface tension of the molecules. Adding soluble impurities increases the surface tension whereas adding sparingly soluble impurity decreases the surface tension.
Why?

Edit: Also, could you please clarify the following: The molecules on the surface experiences a net downward force and hence acts like a stretched membrane. Why does it act like a stretched membrane?
 
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  • #2
Usually the surface tension decreases when temperature is increased.

Soluble impurities can also decrease surface tension, for example methanol or ethanol added to water. Larger-molecule alcohols like n-pentanol that aren't completely water soluble will decrease the surf. tension more effectively because they have a polar and nonpolar end like soap molecules. I don't think there is any general rule relating the solubility of an impurity and its effect on this physical property.
 
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Likes Kaushik
  • #3
hilbert2 said:
Usually the surface tension decreases when temperature is increased.

Soluble impurities can also decrease surface tension, for example methanol or ethanol added to water. Larger-molecule alcohols like n-pentanol that aren't completely water soluble will decrease the surf. tension more effectively because they have a polar and nonpolar end like soap molecules. I don't think there is any general rule relating the solubility of an impurity and its effect on this physical property.
Why does it decrease with temperature? Please check the edit.
 

FAQ: Factors affecting surface tension

What is surface tension?

Surface tension is a phenomenon that occurs at the surface of a liquid, where the molecules are more strongly attracted to each other than to the molecules below. This creates a "skin" on the surface of the liquid, which allows it to resist external forces and maintain its shape.

How is surface tension measured?

Surface tension is typically measured in units of force per unit length, such as newtons per meter (N/m) or dynes per centimeter (dyn/cm). It can be measured using various techniques, including the drop weight method, the capillary rise method, and the Wilhelmy plate method.

What factors affect surface tension?

Several factors can affect surface tension, including temperature, intermolecular forces, and the presence of impurities or surfactants (substances that reduce surface tension). Surface tension also varies depending on the type of liquid, with water having a higher surface tension than most other liquids.

How does temperature affect surface tension?

In general, surface tension decreases as temperature increases. This is because as temperature increases, the kinetic energy of the molecules also increases, causing them to move more and disrupt the cohesive forces between them. As a result, the surface tension decreases.

What are some practical applications of surface tension?

Surface tension has many practical applications, including in everyday activities like washing dishes and doing laundry. It is also important in industrial processes such as oil recovery, inkjet printing, and the production of medicines. In nature, surface tension plays a crucial role in the formation of droplets, bubbles, and the movement of water through plants and insects.

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