Interfacial Phenomenon

Question 1

Def of interface:

Answer 1

boundary between 2 phases

Question 2

Def of surface:

Answer 2

gas-solid or gas-liquid interface

Question 3

Molecule in bulk of liquid have _____ attraction

Answer 3

equal

Question 4

Molecule at surface have ______ cohesive forces

Answer 4

unequal

• results in inward force towards bulk
• creates surface tension

Question 5

Def of surface tension:

Answer 5

force applied parallel to surface per unit length

- intrinsic property

Question 6

Surface tension counteracts…

Answer 6

inward pull and is proportionate to polarity

Question 7

Def of interfacial tension:

Answer 7

force at interface between 2 immiscible liquids

Question 8

Def of cohesion:

Answer 8

strong attractive forces between like molecules

Question 9

Def of adhesion:

Answer 9

strong attractive forces between unlike molecules

Question 10

How does the capillary rise method work?

Answer 10

liquid rises b/c adhesion between liquid and glass is > cohesive forces between liquid molecules
- only measures surface tension

Question 11

How does the DuNoviy method work?

Answer 11

• measures force needed to detach ring that is immersed @ surface/interface
• proportionate to surface/interface tension
• measures both surface and interface tension

Question 12

Def of critical micelle concentration:

Answer 12

concentration of monomer at which micelles form

Question 13

Def of aggregate #:

Answer 13

of monomers that aggregate to form micelle

Question 14

Trend of detergency:

Answer 14

• property that depends on function of monomer
• proportionate to # of monomers
• increase in [detergent] = increase in power

Question 15

Trend of conductivity:

Answer 15

• increase in surfactant = increase in conductivity

- plateaus once it hits CMC b/c surfactant forms micelle

Question 16

Trend of osmotic pressure:

Answer 16

• colligative property
• have to wait until there are enough to make micelle
• depends on # of particles, not size

Question 17

Trend of surface tension:

Answer 17

• inverse property with # of surfactant b/c they start @ surface

Question 18

The longer the C chain, the _____ the HLB

Answer 18

lower

Question 19

Def of wetting:

Answer 19

adsorption that occurs at solid interfaces

Question 20

What counts as high for HLB?

Answer 20

10+

Question 21

Def of contact angle:

Answer 21

angle between surface of solid and wetting agent

• 0 degrees: complete wetting
• 180 degrees: insignificant wetting

Question 22

Def of wetting agent:

Answer 22

SAA that lowers contact angle

- displaces air phase at the surface and replaces it with liquid phase

Question 23

What are some applications of SAA:

Answer 23

• antibacterial
• GI absorptions
• foaming agents
• lung surfactant

Question 24

Why is work needed to move molecule from bulk?

Answer 24

molecule at surface has excess potential E

Question 25

Liquid takes form of ____ surface E

Answer 25

minimal

Question 26

What happens when work is done against surface tension?

Answer 26

increase in liquid surface tension

Question 27

Surfactant affects SA, which makes work…

Answer 27

more favorable

Question 28

Def of spreading:

Answer 28

force of adhesion > cohesive forces

Question 29

Def of work of adhesion (Wa):

Answer 29

E needed to break attraction between different molecule

- proportionate to surface tension

Question 30

Def of work of cohesion (Wc):

Answer 30

E needed to separate like molecules

Question 31

When does spreading occur?

Answer 31

Wa > Wc

- has to be positive in the equation