Zadanie 16b
Wzorowane na: Chemistry HL Paper 3, November 2023, TZ2, 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 is a local anaesthetic. It is made by reacting the carboxylic acid X with ethanol.
(i) Discuss two ways in which the melting point of a crystallized sample of benzocaine can show that it still contains X.
(ii) Deduce the range of wavenumbers in the IR spectrum of the sample that would indicate that it contains X as an impurity. Use section 20 of the data booklet.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) the sample melts gradually over a wider temperature range than a pure sample ✔
the temperature at which it melts is lower than the literature value for pure benzocaine ✔
(ii) 2500–3000 «cm⁻¹» ✔
Schemat punktowania
(i) One mark per way. A vague "different from the literature value" does not earn the second point. (ii) Accept the range 2500–3000 cm⁻¹ described as a very broad band. A single value is accepted only between 2500 and 2850 cm⁻¹, because pure benzocaine itself absorbs strongly from 2850 cm⁻¹ upwards (C–H).
Komentarz
The broad O–H absorbance of the carboxylic acid overlaps the C–H region, but pure benzocaine has no O–H group.