Zadanie 3c
Wzorowane na: Chemistry HL Paper 2, May 2024, TZ2, pytanie 3(c). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Informacja do zadań 3a-3c.
Metal oxides and non-metal oxides behave differently when they dissolve in water, and several of them affect the environment.
Polecenie
Hypochlorous acid, HOCl(aq), has Ka = 2.95 × 10−8.
(i) Determine the pH of an aqueous solution of hypochlorous acid of concentration 0.150 mol dm−3.
(ii) State one assumption you made in the calculation in (i).
(iii) State what a buffer solution based on hypochlorous acid must contain.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) [H+]2 = Ka[HOCl] = 2.95 × 10−8 × 0.150 ✔
[H+] = «» 6.65 × 10−5 «mol dm−3» ✔
pH = 4.18 ✔
(ii) [H+] ≪ 0.150 mol dm−3 «so the equilibrium concentration of HOCl equals its initial concentration»
OR
[H+] from the ionization of water is negligible ✔
(iii) a mixture of HOCl and its conjugate base, OCl−, in comparable amounts «e.g. NaOCl as the source of the base»
OR
partial neutralization of HOCl with a strong base / OH− ✔
Schemat punktowania
(i) M1: expression for [H+]² from Ka (with [H+] = [OCl-]); M2: [H+]; M3: pH. Award [3] for the correct final answer. (ii) [1]. (iii) [1]: accept an OCl- salt as the source of the conjugate base.