Zadanie 16b
Wzorowane na: Chemistry HL Paper 3, November 2023, TZ1, pytanie 16(b). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Polecenie
Benzocaine, a local anaesthetic, is the ethyl ester of 4-aminobenzoic acid. The crude product of its synthesis is purified by recrystallization.
(i) Discuss two ways in which the melting point of the recrystallized benzocaine can show that it still contains impurities.
(ii) Deduce the range of wavenumbers in the IR spectrum of the product that would show that it still contains unreacted 4-aminobenzoic acid. Use section 20 of the data booklet.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) the sample melts over a wider/larger range of temperatures ✔
the sample melts at a temperature below the literature melting point «of pure benzocaine» ✔
(ii) 2500–3000 «cm⁻¹» ✔
Schemat punktowania
(i) M1: a wider melting range. M2: a lower melting point than the accepted value; 'a different value' is not enough, the direction must be given. (ii) [1]: accept any value or range within 2500–3000 cm-1 (the very broad O–H absorption of a carboxylic acid).
Komentarz
The N–H and C=O absorptions occur in both compounds, so only the very broad O–H band of the carboxylic acid distinguishes the acid from the ester.