Zadanie 17
Wzorowane na: Chemistry SL Paper 1, November 2024, pytanie 17. Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Polecenie
An excess of calcium carbonate lumps was added to a beaker of dilute hydrochloric acid, HCl(aq). Carbon dioxide escapes from the beaker, so the mass of the beaker and its contents was recorded against time to give curve 1.
Which change could give curve 2?
A. Using the same mass of calcium carbonate powder instead of lumps
B. Heating the acid before adding the calcium carbonate
C. Using a larger volume of acid of the same concentration
D. Using the same volume of more dilute acid
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
D ✔
«calcium carbonate is in excess, so the acid is the limiting reactant; a lower concentration of the same volume of acid contains fewer moles of HCl, so less CO2 is released and the final mass is higher, and the rate is lower because the concentration is lower; powder and heating only raise the rate and leave the final mass unchanged, while a larger volume of acid releases more CO2 and gives a lower final mass»
Schemat punktowania
One mark for the correct option.
Komentarz
A faster reaction on its own cannot give curve 2: the lowered plateau is the clue that the amount of acid is what changed.