Explain why
(a) The angle of contact of mercury with glass is obtuse, while that of water with glass is acute.
(b) Water on a clean glass surface tends to spread out while mercury on the same surface tends to form drops. (Put differently, water wets glass while mercury does not.)
(c) Surface tension of a liquid is independent of the area of the surface.
(d) Water with detergent dissolved in it should have small angles of contact.
(e) A drop of liquid under no external forces is always spherical in shape.
Answers
Answer:
A. The angle made by the mercury from the glass surface is always obtuse. The adhesive force between the molecules of glass and water is more than the cohesive force between the molecules of water. This results in the formation of a concave meniscus for the surface of water.
B. Water on a clean glass surface tends to spread out while mercury on the same surface tends to form drops. ... Mercury molecules, which make an obtuse angle with glass have a strong force of attraction between themselves and a weak force of attraction toward solids. Hence, they tend to form drops.
C. Surface tension is defined as the force acting per unit length on either side of a imaginary line drawn tangentially on the surface of a liquid.As the force is independent of area of liquid surface taken,so is the surface tension.
D. Water with detergent dissolved in it has small angles of contact (θ). This is because for a small θ, there is a fast capillary rise of the detergent in the cloth. The capillary rise of a liquid is directly proportional to the cosine of the angle of contact (θ).
E. A liquid tends to acquire the minimum surface area because of the presence of surface tension. The surface area of a sphere is the minimum for a given volume. Hence, under no external forces, liquid drops always take a spherical shape.
Answer:
this because when the angle formed is above 90,below 90