Green Chemistry Questions and Answers

Answer: A

Correct answer: near ambient temperature and pressure

Enzymes evolved to work in living cells, so they operate at moderate temperature, near-neutral pH and atmospheric pressure. A transformation that would otherwise need heating and pressure can therefore be run at ambient conditions, which saves energy directly and often improves selectivity so that protecting groups become unnecessary.

Answer: B

Correct answer: replenished on a human timescale

A renewable feedstock is one that regrows within a period comparable with its use, so it is not depleted by being consumed. Nothing else follows automatically: a renewable feedstock is not necessarily cheaper, purer, or of the same composition as its petrochemical counterpart, and its cultivation carries its own impacts.

Answer: C

Correct answer: can be converted into many downstream products

A platform chemical is a versatile intermediate that a biorefinery makes in quantity and from which a range of products can be built, exactly as a small number of building blocks serve a petrochemical complex. It is a starting point rather than an end product, which is what makes the economics of the refinery work.

Answer: D

Correct answer: heating the reacting mixture directly and rapidly

Microwaves are absorbed by the polar molecules of the mixture itself, so the contents are heated directly rather than through the vessel wall, and heating is fast and uniform. Reaction times can fall from hours to minutes, which saves energy. The activation energy and the atom economy are properties of the chemistry and are unchanged.

Answer: A

Bubbles form and collapse violently, and the conditions inside them for a fraction of a microsecond drive chemistry the bulk temperature would not. It is particularly useful for heterogeneous reactions with a solid reagent.

Answer: B

Correct answer: breaks down into innocuous substances

The principle asks that persistence be designed out: at the end of its useful life the product should degrade to harmless materials rather than accumulate. The difficulty is that stability during use and degradability afterwards pull against each other, so the design problem is to place the transition at the right point.

Answer: C

Efficacy and toxicity are separable properties, so a molecule can often be modified to keep the first and lose the second. It requires the structural basis of the toxicity to be understood, which is not always the case.

Answer: D

Correct answer: during the reaction so it can be controlled

In-process analysis lets the operator see the reaction as it proceeds and intervene - stopping at the optimum conversion, avoiding an excursion, preventing an off-specification batch that would become waste. Measuring the effluent afterwards records the loss without preventing it, which is the difference the principle is drawing.

Answer: A

Choosing substances and conditions with less stored hazard reduces what can go wrong, rather than adding protective systems to contain it. Holding a smaller inventory of a dangerous intermediate is the classic application.

Answer: B

Correct answer: adds reagents, steps and waste without building the product

A protecting group must be put on and taken off again, so it contributes two steps, two sets of reagents and two lots of waste, and the molecule ends up exactly where it would have been without it. Designing a route that needs none, often by using a more selective catalyst or enzyme, removes that whole burden.