Zadanie 2c
Wzorowane na: Chemistry HL Paper 3, November 2024, 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.
The formula of an iron oxide can be found by reducing a weighed sample of the oxide to iron metal in a stream of hydrogen gas, H2. The empty reduction tube is weighed before the sample is added. The apparatus is shown.
Polecenie
Suggest why the amount of oxygen per mole of iron calculated from the results is often lower than the true value, and how this error could be reduced.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
reduction incomplete / some oxide not reduced «so oxygen remains in the solid»
OR
the hot iron re-oxidized in air before weighing
OR
impurities in the oxide sample ✔
reheat in hydrogen until the mass is constant
OR
heat for longer / at a higher temperature
OR
spread the sample thinly / increase its surface area
OR
cool the product in hydrogen before weighing ✔
Schemat punktowania
M2 must address the error given for M1. Accept 'weigh the product without exposing it to air'. Do not accept 'not all the oxygen burned' for M1.