Green Chemistry & Sustainability

Q1. (4 marks — 1 each, any four) Accept any four of:

1. Prevention of waste
2. Atom economy (maximise incorporation of materials into product)
3. Less hazardous chemical syntheses
4. Designing safer chemicals
5. Safer solvents and auxiliaries
6. Design for energy efficiency
7. Use of renewable feedstocks
8. Reduce derivatives
9. Catalysis (catalytic reagents preferred over stoichiometric)
10. Design for degradation
11. Real-time analysis for pollution prevention
12. Inherently safer chemistry for accident prevention

Why: These are the standard Anastas & Warner principles guiding waste and hazard reduction.

Q2. (3 marks) Atom economy = a measure of how much of the reactant mass ends up in the desired product. (1) $\% \text{ atom economy} = \frac{\text{mass of atoms in desired product}}{\text{total mass of atoms in reactants}} \times 100 \;\;(2)$

Q3. (4 marks) $M(C_2H_4O) = 2(12)+4(1)+16 = 44$ (1) Desired product mass (2 mol) $= 2 \times 44 = 88$ (1) Reactant mass $= 2(28) + 32 = 56 + 32 = 88$ (1) $\% = \frac{88}{88}\times 100 = 100\%$ (1) Why: All reactant atoms appear in product; addition/oxidation with full incorporation gives 100%.

Q4. (3 marks) $M(C_2H_4Br_2) = 24 + 4 + 160 = 188$ (1) Reactants: $C_2H_4 = 28$, $Br_2 = 160$; total $= 188$ (1) $\% = \frac{188}{188}\times 100 = 100\%$ (1) Why: Addition reactions have 100% atom economy (single product).

Q5. (6 marks — 1 for name + 1 for property, any three)

• Water: non-toxic, non-flammable, cheap, abundant.
• Supercritical CO₂: non-toxic, easily removed by depressurisation, recyclable, non-flammable.
• Ionic liquids: negligible vapour pressure (no VOC emission), thermally stable, tunable.

Q6. (4 marks — 2 reasons × 2)

• Non-toxic, non-flammable and readily available/recyclable. (2)
• Easily separated from products by releasing pressure (returns to gas), leaving no solvent residue; low environmental impact. (2)

Q7. (4 marks) LMP-103S (based on ammonium dinitramide/ADN) and AF-M315E (hydroxylammonium nitrate, HAN-based) are ionic-liquid monopropellants. (1 for identification) Advantages over hydrazine (any two, 1 each + up to 3 marks):

• Much lower toxicity (hydrazine is highly toxic/carcinogenic). (1)
• Higher performance/density (greater specific impulse and density-impulse). (1)
• Safer handling — reduced hazard, no full "SCAPE" suits, lower vapour hazard. (1)

Q8. (4 marks) Cathode (reduction): $2H_2O + 2e^- \rightarrow H_2 + 2OH^-$ (1) Anode (oxidation): $2H_2O \rightarrow O_2 + 4H^+ + 4e^-$ (1) (Acceptable acidic/alkaline versions.) Overall: $2H_2O \rightarrow 2H_2 + O_2$ (2)

Q9. (4 marks) Carbon capture = the process of trapping/removing $CO_2$ produced from industrial processes or power generation to prevent its release to the atmosphere (then storing or using it). (2) Method (any one, 2 marks): Post-combustion capture — flue gases passed through an amine solvent (e.g. monoethanolamine) which absorbs $CO_2$; the $CO_2$ is later released by heating and stored underground. (2)

Q10. (4 marks) (a) $2H_2 + O_2 \rightarrow 2H_2O$ (2) (b) The only product is water; no CO₂ or pollutants are emitted, and the reaction directly converts chemical energy to electricity efficiently. (2)

[
  {"claim":"Ethene oxide atom economy = 100%","code":"M_prod=2*(2*12+4*1+16); M_react=2*(2*12+4*1)+32; ae=Rational(M_prod,M_react)*100; result=(ae==100)"},
  {"claim":"Ethene bromination atom economy = 100%","code":"M_prod=2*12+4*1+2*80; M_react=(2*12+4*1)+2*80; ae=Rational(M_prod,M_react)*100; result=(ae==100)"},
  {"claim":"Molar mass of ethene oxide C2H4O = 44","code":"M=2*12+4*1+16; result=(M==44)"},
  {"claim":"Water electrolysis mass balance: 2H2O -> 2H2 + O2 balances H and O","code":"H_left=2*2; H_right=2*2; O_left=2*1; O_right=2; result=(H_left==H_right and O_left==O_right)"}
]