Zadanie 1d
Wzorowane na: Chemistry SL Paper 2, November 2023, TZ1, pytanie 1(d). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Informacja do zadań 1a-1d.
Ethanoic acid, CH3COOH, belongs to the homologous series of carboxylic acids, in which it is the second member.
Polecenie
Ethanoic acid and propanone, CH3COCH3, each contain a C=O group, and their molar masses are close.
(i) Considering the strongest intermolecular forces in each liquid, explain why propanone boils at a much lower temperature than ethanoic acid.
(ii) Outline why propanone and ethanoic acid each mix with water in all proportions.
(iii) Predict how the electrical conductivities of solutions of ethanoic acid, propanone and nitric acid of equal concentration compare, and explain your prediction. List the three substances in order of increasing conductivity.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) ethanoic acid molecules are held together by hydrogen bonds AND propanone molecules by dipole–dipole forces ✔
more energy is needed to overcome hydrogen bonds than dipole–dipole forces «so ethanoic acid has the higher boiling point» ✔
(ii) each «propanone and ethanoic acid» hydrogen-bonds to water ✔
(iii) propanone < ethanoic acid < nitric acid ✔
the more ions per unit volume, the higher the conductivity «so the order follows the ion concentration» ✔
nitric acid ionizes completely «strong acid» AND ethanoic acid ionizes only slightly «weak acid» AND propanone gives no ions ✔
Schemat punktowania
(i) M1: type of force in each compound; M2: hydrogen bonds stronger. No marks for arguments based on polarity or molar mass, and “van der Waals’ forces” is not an acceptable name for hydrogen bonds. (ii) [1]. (iii) M1: correct order; M2: link between conductivity and ion concentration; M3: strong, weak and non-acidic behaviour. M2 may be implied by the answer to M3.
Komentarz
Propanone is a hydrogen bond acceptor, not a donor, so it hydrogen-bonds with water but not with itself.