Question

1. If you add salt in the water it will breakdown the surface tension, why? Explain.

2. Explain about the capillary action, the convex and the concave phenomena?

Answer 1

1. If you add salt in the water it will breakdown the surface tension. Why? Explain

Before Explaining, the question should be corrected as, why there is an increase in surface tension while adding water to the salt.

Because the surface tension will not breakdown by adding the salt to the water. If the Salt is a Surfactant, which means when there is a reducing effect of surface tension by a compound, it may breaks the surface tension and the question is also correct. But Salt or Sodium Chloride(NaCl) is a strong electrolyte. When it is added with water, it gets dissociated into Cations of Sodium Na⁺ and Anions of Chlorine Cl^-. It destroy some part of the hydrogen bonding between the water molecules by creating a very strong interactions among the Sodium Cations and negative Oxygen parts, and the Chloride anions and positive hydrogen parts. This results in the increase of surface tension of water.

2. Capillary Action

The Property exhibit by the liquid which has the tendency to flow in a thin spaces, independently without any additional support and can overcome the gravity forces which strike in the opposite direction. Some of the materials which show the capillary action will be a thin tube, paper which is a porous material, and liquid carbonfiber which is a non porous material, hairs of paint brush with the color. Capillary action takes place when the cohesive forces within the liquid are weaker than the intermolecular attractive forces between the liquid and the solid surrounding surfaces. Surface tension and the solid surrounding forces or adhesive forces between the container and the liquid will lift the liquid the liquid to the certain extent, when the diameter of the tube is very narrow.

Liquid Column height [latex] h = \frac{2T} {$\rho$ r g} [/latex]

g = acceleration

r = radius of the tube

T = Surface Tension

$\rho$ = liquid density

This equation shows the capillary action is applicable for small tubes, because the liquid lifted height is inversely proportional to the radius of the tube.

Convex and Concave Phenomena

The Surface tension which is created in the top surface of the liquid will be a curve called meniscus. There are two types of meniscus. Convex meniscus and Concave meniscus. When the molecules attracts each other in an energetic manner, than to the material in the container, the convex meniscus arises, as the liquid surface will cave downward. An instance for convex meniscus is mercury and glass in thermometers and barometers. In reverse, the liquid molecules attracted towards the container, the liquid surface cave upwards. Example will be a glass of water.

H – Bottom of the Concave meniscas Br Top of the convex meniscas.