Surface tension

Question 1

Describe the forces acting on the interior molecules

Answer 1

Experience forces from molecules on all sides

Question 2

Describe the forces acting on the surface molecules

Answer 2

molecules on one side => experience attractive forces pulling them into interior

Question 3

What is the result of the imbalanced force acting on the surface molecules?

Answer 3

Surface rearranged => minimum amount of molecules form surface => SA minimised, SA:V smallest ratio
=> surface molecules more packed and ordered than the rest

Question 4

Define surface tension

Answer 4

inward molecular attraction forces

=> must be overcome to increase SA

Question 5

Define interfacial tension

Answer 5

Surface investigated is interface of 2 liquids

Question 6

Define bubble

Answer 6

Region trapping vapour/air by thin film => 2 x SA of a cavity due to 2 surfaces

Question 7

Define cavity

Answer 7

Vapour filled hole in a liquid

Question 8

Define droplet

Answer 8

small volumes of liquid at equilibrium surrounded by their vapour
=> P(concave) > P( convex) at interface

Question 9

Define capillary action

Answer 9

adhesive forces between wall and liquid => upward force at surface edge
=> meniscus forms - turn upwards

Question 10

Describe effects of temperature on surface tension

Answer 10

Surface tension decreases as temp increases

Question 11

Define cohesive forces

Answer 11

bind molecules of same type together - meniscus sad face when cohesive > adhesive

Question 12

Define adhesive forces

Answer 12

binds substance to a surface - meniscus happy face when adhesive > cohesive

Question 13

Explain why the surface tension of a branched aliphatic molecule is greater than a normal straight chain
aliphatic with the same total number of carbon atoms.

Answer 13

Branched molecules have smaller SA and are more compact than straight chained. Branched causes entanglement of molecules - more force required