Green Chemistry Questions and Answers

Answer: A

Correct answer: reduce or eliminate the use and generation of hazardous substances

The definition puts the emphasis on design rather than on treatment: the hazard is to be designed out at the outset, not managed after it exists. That is what distinguishes green chemistry from pollution control, and it is why the discipline belongs to the chemist rather than to the effluent engineer.

Answer: B

Correct answer: prevent waste than to treat or clean it up

The first of the twelve principles establishes the whole approach. Waste that is never made needs no treatment, no storage, no transport and no disposal, and it carries no residual liability. Every treatment, however good, leaves something and costs something, so prevention is preferable wherever it is achievable.

Answer: C

Correct answer: design stage of the process

End-of-pipe control accepts the process as given and cleans up what emerges; green chemistry changes the process so that less emerges. Acting at the design stage is cheaper, because the cost of treatment plant is avoided altogether, and more effective, because a hazard that is not created cannot escape.

Answer: D

It is computed from the balanced equation alone and is fixed by the chemistry chosen, whatever the operator does. Percentage yield measures how well the reaction was run; atom economy measures whether it was the right reaction.

Answer: A

Correct answer: much of the reactant mass leaves as by-product

Yield and atom economy answer different questions. Yield asks how much of the theoretical product was obtained; atom economy asks how much of the reactant mass ends up in that product at all. A reaction that converts every molecule of substrate but sheds most of its mass as a by-product has a perfect yield and a poor atom economy.

Answer: B

Correct answer: incorporates all of the reactants into the product

In an addition every atom of both reactants appears in the product, so the atom economy is one hundred per cent by construction. A substitution expels a leaving group, which is waste by definition, and the larger that group the worse the economy. This is why addition and rearrangement are the preferred reaction types.

Answer: C

Correct answer: elimination

An elimination discards a fragment from the substrate itself, so mass is lost from the very molecule being built and none of it can be recovered in the product. Rearrangement and cycloaddition retain all the atoms and addition combines both reactants entirely, so all three score far better.

Answer: D

Correct answer: waste per unit mass of product

The E-factor is kilograms of waste per kilogram of product, so a low figure is good and zero would be perfect. It rises from about 0.1 in bulk petrochemicals to 25 or more in fine chemicals and often above 100 in pharmaceuticals, which is what first drew attention to how wasteful complex syntheses are.

Answer: A

Correct answer: mass of solvent and auxiliaries used

Atom economy is computed from the balanced equation and therefore sees only the reagents that appear in it. Solvent, water, drying agents and chromatography media appear nowhere in the equation and yet are usually the largest part of the mass consumed. The E-factor counts everything that leaves as waste, which is why the two figures can point in opposite directions.

Answer: B

It includes reactants, solvents, water and processing aids, so it is the most comprehensive of the common metrics and differs from the E-factor by exactly one. The pharmaceutical industry adopted it as its standard measure.