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 = 2RCOO-(aq) + Ca2+(aq) –> (RCOO)2Ca(s))
- anionic detergents struggle (form soluble complexes with the 2 ions = reduce reaction efficiency) (although phosphate builders can precipitate with the ions)
- neutral non-anionic and cationic 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
- used for personal hygiene

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
- used for dishwashing liquid or bath cleaners

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
- used for emulsifying and solubilising agents in laboratory work

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

Question 9

saponification

Answer 9

1. esterification to produce triglyceride
   glycerol + fatty acid –> triglyceride + water
2. saponification
   triglyceride + 3(sodium hydroxide) –> glycerol + salt (soap)