Zadanie 2a
Wzorowane na: Chemistry SL Paper 3, May 2024, TZ2, pytanie 2(a). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Informacja do zadań 2a-2b.
Green chemistry aims to design chemical processes that produce less waste, use less energy and avoid hazardous substances. Four metrics used to judge how green a process is are defined in the table.
| Metric | Definition |
|---|---|
| Process mass intensity (PMI) | total mass of all materials used in the process (reactants, solvents, water, reagents and process aids) divided by the mass of the desired product |
| E-factor | mass of all waste, including used solvents, divided by the mass of the desired product |
| Atom economy | mass of the desired product divided by the total mass of the reactants in the balanced equation |
| Eco-Scale | 100 minus the sum of the penalty points given for low yield, hazardous chemicals, unconventional equipment and prolonged heating |
Polecenie
(i) The ideal PMI, which corresponds to the greenest possible process, is 1. Estimate the ideal value of each of the other three metrics.
(ii) Identify the metric in the table that cannot be affected by the choice of solvent.
(iii) Suggest one reason why the PMI for making a pharmaceutical is much greater than the PMI for making ammonia by the Haber process.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) E-factor: 0 ✔
atom economy: 1 «or 100 %» ✔
Eco-Scale: 100 ✔
(ii) atom economy ✔
(iii) any one of:
the synthesis has many steps, each needing solvents and purification ✔
OR
large masses of solvents/process aids are used for a small mass of product ✔
OR
low yields/many side products have to be separated ✔
OR
the Haber process is a single continuous step without solvent in which unreacted gases are recycled ✔
Schemat punktowania
(i) Award [2] for three correct values and [1] for two; accept "100 %" for 1 and "0 %" for 0. (ii) [1]: only atom economy, which counts the reactants in the balanced equation alone. (iii) [1]: any one reason; apply the list principle.