Interfaces

Question 1

List some interfaces

Answer 1

• oil and water
• air and liquid
• air and solid
• liquid and solid

Question 2

Surface tension

Answer 2

Force acting on the surface of a liquid that tends to minimise surface area

Question 3

Surface free energy

Answer 3

1) the work required to increase the surface area by 1m2
2) free energy and surface tension are numerically equal with units N M-1
- unbalanced forces at the surface tends to lead to a net inward force of attraction on surface molecules that tends to minimise the area of the surface (surface tension )
- contraction if the surface therefore leads to a minimum free energy state and work is required to increase surface area

Question 4

How do we measure surface tension?

Answer 4

1) Wilhelmy plate method -thin plate that can be wetted by the liquid. Force acting on the late due to wetting is measured by a balance and is proportional to surface tension
2) capillary rise method

Question 5

Interfaces

Answer 5

Two phases mutually insoluble