Zadanie 2b
Wzorowane na: Chemistry HL Paper 2, May 2022, TZ1, pytanie 2(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 2a-2c.
Zinc is a reactive metal that is found in alloys such as brass.
Polecenie
A block of zinc attached to a steel structure acts as a sacrificial anode.
(i) Calculate the standard cell potential, in V, of a cell made from zinc and steel half-cells. Use section 19 of the data booklet and take the standard electrode potential of steel to be that of iron.
(ii) Calculate ΔG⊖, in kJ, for the cell reaction. Use sections 1 and 2 of the data booklet.
(iii) Dissolved oxygen is reduced to hydroxide ions at the steel surface. State the half-equation for this process.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) Ecell⊖ «= −0.45 V − (−0.76 V)» = «+»0.31 «V» ✔
(ii) ΔG⊖ = −nFE⊖ AND n = 2 ✔
ΔG⊖ «= −2 × 9.65 × 104 C mol−1 × 0.31 V» = −59 830 «J» = −59.8 «kJ» ✔
(iii) O2 + 2 H2O + 4 e− → 4 OH− ✔
OR
✔
Schemat punktowania
(i) [1]. (ii) M1: n = 2 with the equation; M2: value in kJ. If n = 1 is used, award [1] for −29.9 kJ. A positive 59.8 kJ earns [1] in total. ECF from (i). Accept values from −59.8 to −60 kJ. (iii) [1]; accept equilibrium arrows. Ignore state symbols.