Question

The surface tension of mercury at normal temperature compared to that of water is
A) More
B) Less
C) Same
D) more or less depending on the size of glass tube

Answer 1

Surface tension is the property of liquid which tends to minimize the surface area due to the interatomic attraction between molecules at the surface. Since this is an intrinsic property of liquid, it doesn’t depend on any external factor and varies from liquid to liquid.

Complete step by step answer:
The interatomic attraction force of mercury is much greater than that of water and so the surface tension of the mercury is. It can be understood from a very simple observation. If you notice a drop of mercury and a drop of water, you will always get to see that the bead of mercury will always bow over more than the bead of water for the same mass of respective liquids. Surface tension occurs due to the difference in inner and outer forces experienced by the molecules at the surface. Hence, the more the surface tension the more round the bead of the liquid becomes.

Correct answer:
The surface tension of mercury at normal temperature compared to that of water is (a) more.

Note: A student might get confused by the information that when a capillary tube is inserted inside water then water rises through it but in case of mercury water level goes down. If you think this happens because surface tension of mercury is negative and lesser than that of water then you’re wrong. This happens because the contact angle between mercury and glass is 135 degree and cosine of this angle produces negative signs. But the surface tension amount of mercury doesn’t depend on these external factors, and for mercury it’s greater.