Answers to questions on Biochemistry & the environment

1. (a) Dichlorodiphenyltrichloethane

(b) It is thermodynamically stable so does not break down easily and it has very little polarity so is able to form weak intermolecular van der Waals’ type forces of attraction with molecules of fat.

(c) The DDT is absorbed by insects, which are then eaten by small animals, which in turn are eaten by larger animals. At each stage of the food chain the concentration of the DDT in the body increases. Birds of prey are relatively high up the food chain. This is an example of biomagnification.

(d) Mass of products = mass of reactants.

Mass of molar products = (14 x 12.01) + (11 x 1.01) + (5 x 35.45) + 16.00 = 372.50 g.

This contains 354.48 g of DDT and 18.02 g of water.

Atom economy = (354.48 ÷ 372.50) x 100 = 95.2%

(e) (i) Overall reaction is : H₃CCHO + 3Cl₂ → Cl₃CCHO + 3HCl

Mass of molar products = 147.38 + (3 x 36.46) = 256.76 g

Atom economy = (147.38 ÷ 256.76) x 100 = 57.4%

(ii) The HCl produced can be recycled either to use as the hydrochloric acid solvent or oxidised to produce chlorine so it is no longer a waste product.

2. Host-guest chemistry describes complexes composed of two or more molecules or ions (the larger being the host and the smaller being the guest) that are held together in unique 3-D structural relationships by non-covalent forces. The forces of attraction between the host and the guest include hydrogen bonding, van der Waals’ attraction and ionic bonding. These are weaker than covalent bonds and enable the 3-D structure to be maintained but only temporarily rather than permanently.

3. Any three from:

1. Ester, amide and ether groups, unlike the C-C bonds in many non-biodegradable polymers, can be hydrolysed by microorganisms/enzymes that occur naturally or broken down more easily by other factors, such as change in pH or temperature.

2. Biodegradable polymers tend to be more soluble in water than non-biodegradable polymers, which enable better interaction with the enzymes.

3. When they are broken down into smaller units the products can be natural substances, e.g. sugars, which can easily be further broken down by enzymes.

4. They tend to have less branching than non-biodegradable polymers. This increases the number of end groups per unit mass where degradation normally starts.

Answers to Biochemistry & the environment questions