Zadanie 3b
Wzorowane na: Chemistry HL Paper 2, November 2024, pytanie 3(b). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Polecenie
(i) A dilute aqueous solution of sodium chloride is electrolysed using inert electrodes. Give the half-equation for the process at the anode and the half-equation for the process at the cathode. Use section 19 of the data booklet.
(ii) Identify the product at the anode when a concentrated aqueous solution of sodium chloride is electrolysed using inert electrodes.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) anode (positive electrode): 2 H2O(l) → O2(g) + 4 H+(aq) + 4 e−
OR
4 OH−(aq) → O2(g) + 2 H2O(l) + 4 e− ✔
cathode (negative electrode): 2 H2O(l) + 2 e− → H2(g) + 2 OH−(aq)
OR
2 H+(aq) + 2 e− → H2(g) ✔
(ii) chlorine / Cl2 ✔
Schemat punktowania
(i) M1: oxygen formed at the anode; M2: hydrogen formed at the cathode. Correct equations placed on the wrong electrodes earn [1] at most. An equation that produces chlorine does not earn M1. Accept equations written for one electron or two electrons per species; ignore state symbols and reversible arrows. (ii) [1].
Komentarz
In a dilute solution water is oxidized in preference to chloride ions; in a concentrated solution chloride ions are oxidized.