Zadanie 2b
Wzorowane na: Chemistry SL Paper 3, May 2024, TZ2, pytanie 2(b). 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
Two methods of making ethyl ethanoate are compared using the Eco-Scale. The penalty points are given in the table.
| Parameter | Penalty points |
|---|---|
| N (dangerous for the environment) | 5 |
| T (toxic) | 5 |
| F (highly flammable) | 5 |
| F+ (extremely flammable) | 10 |
| Yield | |
| Unconventional activation, for example microwave heating | 2 |
| Inert gas atmosphere | 1 |
| Heating for less than 1 hour | 2 |
| Heating for more than 1 hour | 3 |
Method 1: ethanoic acid reacts with ethanol, with concentrated sulfuric acid as the catalyst. The mixture is heated in a microwave reactor for 40 minutes and the yield is 68 %. The hazard codes of the reagents are ethanoic acid (F) and ethanol (F).
Method 2: ethanoyl chloride reacts with ethanol in the presence of pyridine, under a dry nitrogen atmosphere, at room temperature for 30 minutes. The yield is 88 %. The hazard codes of the reagents are ethanoyl chloride (F, T), ethanol (F) and pyridine (F, T).
(i) Determine the Eco-Scale value for Method 1, ignoring the sulfuric acid catalyst.
(ii) Suggest one reason why Method 2 has a lower Eco-Scale value than Method 1.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) total penalty points «= 5 + 5 + + 2 + 2 = 10 + 16 + 2 + 2 =» 30 ✔
Eco-Scale «= 100 − 30 =» 70 ✔
(ii) any one of:
more of the reagents earn penalty points «ethanoyl chloride and pyridine are both flammable and toxic» ✔
OR
the penalty points for the reagents are greater «25 compared with 10» ✔
OR
it needs an inert nitrogen atmosphere, which Method 1 does not ✔
OR
it uses more toxic reagents ✔
Schemat punktowania
(i) M1: the penalty points added up, including the halved yield penalty. M2: subtraction from 100. ECF from M1. Award [1 max] if one penalty is omitted or if the yield penalty is not halved. (ii) [1]: any one reason; apply the list principle. A lower yield is not accepted, because Method 2 has the higher yield.
Komentarz
Method 2 scores 68: penalty points 25 for the reagents, 6 for yield and 1 for the inert atmosphere.