Week 4 Material

Question 1

What is a colloid?

Answer 1

A mixture where tiny particles of one substance are dispersed throughout another, but they don’t settle out over time. These particles are larger than those in a solution but smaller than those in a suspension

Question 2

Applications of colloids

Answer 2

• Recovery of metals from ores
  
  • Explosives
  • Extractions
  • Coatings
  • Paints
  • Lubricants and cutting fluids
  • Fertilizers
  • Water purification
  • Food
  • Cleaning products
  • Consumer care products
  • Pharmaceutical delivery devices
  • Clean energy

Question 3

Sol

Answer 3

• solid in a liquid
• Eg. Gold atoms in water
  OR
• solid in a solid
• Eg. Ruby glass (gold in glass sol)

Question 4

Aerosol

Answer 4

• liquid in a gas
• Eg. fog, sprays
  OR
• solid in a gas
• Eg. smoke

Question 5

Emulsion

Answer 5

• liquid in a liquid
• Eg. milk, paints, mayo

Question 6

Gel

Answer 6

• solid in a liquid
• Eg. Jelly

Question 7

Foam

Answer 7

• liquid in a gas
• Eg. shaving cream
  OR
• solid in a gas
• Eg. marshmellow

Question 8

What are hydrophobic colloids?

Answer 8

• weak attractive forces between the water
• surfaces of the colloidal particles
• Eg. emulsion droplets, hydrophobic polymers

Question 9

what are hydrophillic colloids?

Answer 9

• strongly attracted to water
• functional groups (-OH, -NH2) which forms strong H-bonds
• Eg. mineral oxides (silica, proteins, starch)

Question 10

are colloids a spontaneous or nonspontaneous reaction?

Answer 10

• not spontaneous
• requires energy

Question 11

are colloids thermodynamocally stable?

Answer 11

• unstable
• large surface area
• long range = collapse into single blob - van der waals forces

Question 12

are colloids stable?

Answer 12

• hydrophobic colloid is stablised by positve ion absorbed onto each particle and a secondary layer of negative ion

Question 13

what is a surfactant

Answer 13

• surface, active, agent
• species that accumulates at the interface of two phases or substances that modifies the properties of the surface

Question 14

what are the 4 basic classes of surfactants?

Answer 14

1. ionic: anionic/cationic which dissociate in water into two oppositely charged species
2. non ionics: highly polar moiety
3. zwitterionic (amphoteric): both + and - groups

Question 15

what are emulsions

Answer 15

• disperion of two immiscible liquids
• shaking two components together
• emulsifying agent stabilises that product
• can be a soap, surfactant of iyophilic sol

Question 16

what is the molecular orbital theory?

Answer 16

• atomic orbitals from different atoms in a molecule are mathematically combined to form molecular orbits spanning two or more atoms

Question 17

what is band theory?

Answer 17

• MO are constructed from the valence orbitals on each atom are delocailsed over all atoms
• MOs so close together are indistiguishable
• band is composed of as many molecular orbitals as there are contrubiting atomic orbitals

Question 18

what is the fermi level?

Answer 18

• in metals band gap is small
• at temps above 0K, the thermal energy causes the electrons to occupy higher energy orbitals
• can result in:
  1. a negative electron on the orbital above Fermi level
  2. a positve hole from the absence of an electron below the Fermi level

Question 19

what is an alloy?

Answer 19

• mixtue of metals or with a non-metal
• two metals with different electronegativities t