Zadanie 1a
Wzorowane na: Chemistry HL Paper 3, May 2024, TZ2, pytanie 1(a). 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-1b.
The decomposition of aqueous hydrogen peroxide is catalysed by iodide ions:
2 H2O2(aq) → 2 H2O(l) + O2(g)
Polecenie
State one method that could be used to follow the progress of this reaction and explain how its measurements allow the rate, in mol dm−3 s−1, to be determined.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
ALTERNATIVE 1
collect the oxygen in a gas syringe/measure the volume of gas released ✔
the amount of O2 is proportional to the volume of gas «and equals half the amount of H2O2 decomposed» ✔
ALTERNATIVE 2
measure the mass of the reaction flask on a balance «the mass falls as oxygen escapes» ✔
the mass lost is proportional to the amount of O2 released ✔
ALTERNATIVE 3
withdraw samples at intervals, quench them and titrate with acidified potassium manganate(VII) ✔
the titre is proportional to the concentration of H2O2 remaining in the sample ✔
FOR ALL ALTERNATIVES
the measurement is repeated at known time intervals «and converted to concentration, so that rate = change in concentration/time» ✔
For a gas-volume method, convert each oxygen reading to moles using PV = nRT (or the molar gas volume), then divide by the reaction-solution volume in dm3 before finding the change per second. Multiply oxygen amount by two if following peroxide consumption.
Schemat punktowania
M1: a suitable measurement. M2: the measured quantity linked to the amount or concentration of reactant or product. M3: the measurement followed against time. Award [2 max] for two different correct methods, M1 only for each. Accept other valid methods, for example a pressure sensor in a sealed flask. Accept "weight" for "mass". M3 must refer to the measurement being repeated over time.