Topic 7 Flashcards
1
Q
Define cohesion
A
- Attractive forces between alike substances
- Responsible = surface tension
2
Q
Define adhesion
A
- Attractive forces between unlike substances
- Responsible = capillary action
3
Q
Define surface tension
A
- Property of liquid surface
- Due to IMF = resist surface deformation
- Reduces surface area
4
Q
How can surface tension be measured?
A
- Force required to hold in place wire stretching film of liquid
5
Q
What is the formula for surface tension?
A
γ = F/L
- Nm-1
6
Q
Describe the pressure in a bubble
A
- Pressure inside > outside = doesn’t collapse
7
Q
Give the formula for pressure in a bubble
A
ΔP = Pint - Pext = 4𝛾/r
8
Q
What happens when 2 bubbles collide?
A
- Air flows from small > larger = from high pressure > low
9
Q
Define surfactant
A
- When added to a liquid = reduces surface tension
- Concentrates near the surface
- Have hydrophilic + hydrophobic side
- E.g soap
10
Q
Define interfacial tension
A
- Tension at point of contact
- Liquid + non-mixing liquid/solid
11
Q
Describe interfacial tension between water + oily surface
A
- Causes beading
- Cohesive forces > adhesive forces
- Compact droplet = large contact angle
12
Q
Describe interfacial tension between water + hydrophilic surface
A
- Adhesive forces > cohesive forces
- Droplet spreads out = low contact area
13
Q
What are the contact angles?
A
ON FLAT SURFACE
- > 90 = beading
- < 90 = wetting
IN VERTICAL TUBE
- Adhesive > cohesive = negative meniscus
- Cohesive > adhesive = positive meniscus
14
Q
Describe capillarity
A
- Thinner the tube = more liquid rises up
15
Q
What is the formula for capillary action?
A
h = 2𝛾𝑐𝑜𝑠θ/𝜌𝑔r
