Zadanie 3e
Wzorowane na: Chemistry HL Paper 1B, May 2026, TZ2, pytanie 3(e). 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
(i) The diagram shows the burette scale at the end of trial 4. The solution is deep purple, so the reading is taken at the top of the liquid. Determine the final burette reading for trial 4 and complete the table.
| Burette reading / cm3 (± 0.05 cm3) | Trial 1 | Trial 2 | Trial 3 | Trial 4 |
|---|---|---|---|---|
| initial | 0.20 | 1.35 | 0.75 | 3.40 |
| final | 19.20 | 20.30 | 19.80 | ? |
(ii) Suggest, with a reason, whether more trials should be carried out.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz CKE i punktacja
Odpowiedź z klucza
(i) 22.35 «cm3» ✔
(ii) no AND the four titres «19.00, 18.95, 19.05 and 18.95 cm3» agree within 0.10 cm3/are concordant ✔
Schemat punktowania
(i) [1] for 22.35; accept 22.30 to 22.40 «cm3». (ii) [1] for no with a reason based on concordant titres; a decision without the reason scores 0.
Komentarz
The scale increases downwards and has marks every 0.1 cm3, so a reading between two marks is estimated to the nearest 0.05 cm3.