surfactants

Question 1

in presence of a non-polar substance the action of surfactants on the water

Answer 1

• hydrophilic head in water and hydrophobic tail sticking out in a line
• dissolve to form spherical micelles (repel each other) with head outside and tail inside
• if non-polar substances are stuck onto a surface:
  1. surfactant dissolves in water
  2. monolayer formation in grease
  3. agitation separates grease from surface
  4. micellisation and emulsifica

Question 2

parts of a surfactant

Answer 2

• polar hydrophilic head (water loving, interacts with water, H-bond and dipole dipole and dispersion)
• non-polar hydrophobic tail (water hating, interacts with oil, dispersion forces)

Question 3

what is hard water

Answer 3

is impure water which contains >20ppm of Ca2+ or Mg2+ ions
- soaps struggle (carboxylate ion precipitates with the 2 ions to form a solid called scum
- anionic detergents struggle (form soluble complexes with the 2 ions although phosphate builders can precipitate with the ions)
- neutral non-anionic detergents are not affected (don’t react with Ca2+ and Mg2+)

Question 4

what is a soap

Answer 4

a soap is an ion with a long non-polar alkyl tail and a polar charged carboxylate head (usually present in Na and K salts) (from natural oils and fats)

Question 5

what is an anionic detergent

Answer 5

is an ion with a ion with a long non-polar alkyl tail and a polar anionic sulfate or benzenesulfonate head (usually present in Na and K salts) (too harsh for personal hygiene)

Question 6

what is a non-anionic detergent

Answer 6

is a molecule with a long non-polar alkyl tail and a polar repeating uncharged polyethylene glycol head
- ends in an alcohol group

Question 7

what is a cationic detergent

Answer 7

is an ion with a long non-polar alkyl tail and a polar cationic trimethylammonium or quaternary ammonium head (usually present in Cl or Br salts) (biocidal reduces static friction and tangling)

Question 8

what are surfactants

Answer 8

soaps and detergents are surfactants and they are more effective at cleaning than water alone
- used to clean non-polar substances from surfaces
- soaps are produced from natural sources while detergent is made from artificial products
- surfactants have 2 parts: hydrophilic head and hydrophobic tail