Zadanie 2c
Wzorowane na: Chemistry HL Paper 2, May 2022, TZ1, pytanie 2(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 2a-2c.
Zinc is a reactive metal that is found in alloys such as brass.
Polecenie
The graph shows the volume of hydrogen produced when a small piece of zinc reacts with a large excess of 2.0 mol dm−3 hydrochloric acid.
(i) Deduce from the graph how the rate of reaction depends on the amount of zinc present.
(ii) The rate is first order in HCl. Calculate how long, in seconds (s), it would take for half of the zinc to dissolve if [HCl] were 0.50 mol dm−3.
(iii) Following the loss in mass is a common way to study reactions that give off carbon dioxide. Suggest why it is a poorer choice for zinc and hydrochloric acid.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) independent of / not dependent on the amount of zinc «the volume rises at a constant rate until all the zinc has reacted» ✔
OR
zero order with respect to zinc ✔
(ii) half of the zinc gives 36 cm3 of gas, reached at 180 s with 2.0 mol dm−3 HCl ✔
the concentration is four times smaller, so the rate is four times smaller and the time is 4 × 180 s = 720 «s» ✔
(iii) the mass lost «hydrogen» is very small «relative to the mass of the flask contents» / the percentage uncertainty in the mass loss is too great ✔
OR
the molar mass / density of H2 is much lower than that of CO2 ✔
Schemat punktowania
(i) [1]. (ii) [1] for 720 s; accept 700-740 s. (iii) [1]. Accept “the balance cannot detect such a small change in mass”.