Zadanie 7b
Wzorowane na: Chemistry HL Paper 3, November 2023, TZ1, pytanie 7(b). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Polecenie
Palmitic acid, CH3(CH2)14COOH, and palmitoleic acid, CH3(CH2)5CH=CH(CH2)7COOH, which has a cis C=C double bond, both have a chain of sixteen carbon atoms. Predict which of the two fatty acids has the higher melting point and give two reasons for your choice.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
palmitic acid AND stronger London/dispersion forces between its molecules ✔
saturated/no C=C bond, so the chains are straight and the molecules pack closer together
OR
the cis double bond of palmitoleic acid puts a kink in the chain, so its molecules pack less closely ✔
Schemat punktowania
M1: palmitic acid with stronger London forces. M2: saturated chain, or the kink caused by the cis double bond, leading to closer packing. Do not accept arguments based on size or molar mass; do not award M2 if palmitoleic acid is chosen.
Komentarz
The two acids have the same chain length, so the difference in melting point cannot be explained by molecular size.