Zadanie 2d
Wzorowane na: Chemistry HL Paper 3, May 2023, TZ2, pytanie 2(d). 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-2d.
A student investigated how much spinach would supply the recommended daily intake of iron. The student
- weighed 63.2 g of spinach leaves and blended them with 600 cm3 of water
- boiled the mixture, filtered it and allowed the filtrate to cool
- pipetted 10.0 cm3 of the filtrate into 20.0 cm3 of 1.00 mol dm−3 sulfuric acid in a flask
- titrated the mixture with 0.00100 mol dm−3 potassium manganate(VII) solution.
The reaction taking place is:
5 Fe2+(aq) + MnO4−(aq) + 8 H+(aq) → 5 Fe3+(aq) + Mn2+(aq) + 4 H2O(l)
Polecenie
The result is roughly 30 times higher than the iron content of spinach given in reference tables (as a percentage by mass). Suggest one reason, apart from human error, for so large a difference.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
any one of:
other compounds in the extract «such as ascorbic acid/vitamin C or polyphenols» are also oxidized by manganate(VII), which uses up extra titrant ✔
OR
iron from the blender blades/water/container was added to the sample ✔
OR
the spinach used was not representative «a different variety, grown in different soil» ✔
OR
the concentration of the manganate(VII) solution changed over time ✔
Schemat punktowania
[1]: any one valid reason that is not human error. Accept "sample dried out/was dehydrated".