Zadanie 3b
Wzorowane na: Chemistry HL Paper 1B, May 2026, TZ2, pytanie 3(b). 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-3f.
A titration was performed to find the concentration of iron(II) ions in a solution made from iron tablets. Portions of 25.00 cm3 of the iron(II) solution were acidified with excess dilute sulfuric acid and titrated with potassium manganate(VII) solution, which acts as its own indicator.
MnO4−(aq) + 5 Fe2+(aq) + 8 H+(aq) → Mn2+(aq) + 5 Fe3+(aq) + 4 H2O(l)
A standard 0.0200 mol dm−3 potassium manganate(VII) solution was used in a preliminary trial. The volume of titrant required was less than 5 cm3, so the standard solution was diluted before the main titrations.
Polecenie
Suggest why diluting the standard solution was necessary.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz CKE i punktacja
Odpowiedź z klucza
a titre of under 5 cm3 has a large percentage uncertainty «two readings of ±0.05 cm3 give ±0.10 cm3, over 2 % of 4.75 cm3» ✔
OR
the diluted solution gives a larger titre, so the percentage uncertainty in the volume is smaller ✔
Schemat punktowania
[1] for a reference to the uncertainty of the burette readings relative to a small volume. 'To make the titration easier' scores 0.