Topic 14: Polymers & Biopolymers

Question 1

Describe the structure of fatty acids, fats and oils

Answer 1

• Long chain carboxylic acids - long hydrocarbon chain attached to a -OH group
  + Saturated: single bond chain
  + Mono/polyunsaturated: 1 or more double bonds in the chain
• Fats and oils: esters of fatty acids and alcohols
  + fatty acids react with glycerol (a 3 -OH alcohol)
  + forms triester aka triglycerides

Question 2

Compare the melting point of saturated and unsaturated fatty acids

Answer 2

• Saturated: single bonds –> pack really well –> high melting point
• Unsaturated: double bonds in between –> less able to pack well –> lower melting point

Question 3

How is soap related to the hydrolysis of fats?

Answer 3

Fats are heated with NaOH –> hydrolysis happens to dissociate the H+ and produce carboxylate salts
The carboxyl group is now charged –> hydrophilic and the chain is hydrophobic

Question 4

How do the physical properties of soap allow it to wash away fatty dirt particles?

Answer 4

When soap is dissolved in water, the molecules cluster into micelles with the fatty acids chain in the middle to avoid water. When they cluster, they also take in the fatty dirt particle as these particles are hydropobic too –> wash away with water

Question 5

How are amino acids and its zwitterion form related?

Answer 5

A molecule cannot exist in a form with both acidic and basic functional groups as these 2 groups will react with each other to form an internal salt (dipolar ion) → an alpha-amino acid in its actual form is called zwitterrion

NH2 becomes protonated to NH3+
COOH becoems deprotonated to COO-

Question 6

Differentiate condensation and addition polymerisation

Answer 6

• Condensation: ejection of a small molecule in gaseous form when monomers are combines
  + conducted above boiling point of the molecules being ejects –> lost as gas, not affect the reaction
• Addition: addition of alkene monomers to a growing chain
  + requires catalyst