Zadanie 1d
Wzorowane na: Chemistry SL Paper 2, November 2023, TZ2, 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, is the carboxylic acid that gives vinegar its sour taste.
Polecenie
Ethanoic acid and propanone, CH3COCH3, both contain a carbonyl group and have similar molar masses.
(i) Explain, in terms of the strongest intermolecular forces present in each liquid, why propanone boils at a much lower temperature than ethanoic acid.
(ii) Outline why propanone and ethanoic acid are both fully miscible with water.
(iii) Predict the order of electrical conductivity of solutions of ethanoic acid, propanone and hydrochloric acid that all have the same concentration, and explain your order. Give the order in the form: lowest < middle < highest.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) «strongest forces:» hydrogen bonds between ethanoic acid molecules AND dipole–dipole forces between propanone molecules ✔
hydrogen bonds are stronger than dipole–dipole forces «so more energy is needed to separate ethanoic acid molecules, giving the higher boiling point» ✔
(ii) both can form hydrogen bonds with water molecules ✔
(iii) propanone < ethanoic acid < hydrochloric acid ✔
electrical conductivity depends on the concentration of ions in solution
OR
the solutions contain increasing concentrations of ions in this order ✔
hydrochloric acid is a strong acid / is fully ionized AND ethanoic acid is a weak acid / is partially ionized AND propanone is not an acid / does not ionize ✔
Schemat punktowania
(i) [2]: M1 for the correct type of strongest force in each substance, M2 for the comparison of strengths. Do not award marks for explanations based on molar mass or on polarity alone, and do not accept London (dispersion) forces as the strongest force in propanone. (ii) [1]. (iii) [3]: M1 for the complete correct order, M2 for linking conductivity to ion concentration (may be implied by M3), M3 for the extent of ionization of the three substances. Accept equations with appropriate arrows for M3.