Zadanie 3a
Wzorowane na: Chemistry SL Paper 2, May 2023, TZ2, pytanie 3(a). 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-3b.
Electrolysis and the Winkler method for dissolved oxygen are both applications of redox reactions.
Polecenie
Molten lithium bromide, LiBr(l), is electrolysed using inert graphite electrodes, as shown in the diagram.
(i) Identify the product formed at the cathode.
(ii) State the direction in which the electrons flow in the external circuit, referring to the battery and to the two electrodes.
(iii) Describe the arrangement of the carbon atoms in graphite and explain why graphite, unlike diamond, conducts electricity.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) lithium / Li «metal» ✔
(ii) electrons flow from the anode «right-hand electrode» to the positive terminal of the battery
OR
from the negative terminal of the battery to the cathode «left-hand electrode» ✔
(iii) carbon atoms are arranged in layers «hexagonal rings, each carbon bonded to three others in a covalent network within the layer» ✔
each carbon atom has one electron that is delocalized and free to move along the layers, carrying charge «in diamond all four electrons are held in localized bonds» ✔
Schemat punktowania
(i) [1] for lithium; do not accept lithium ions or Li+. (ii) [1] for a correct direction of flow in the external circuit, either from the anode to the battery or from the battery to the cathode. Do not award the mark if electrons are shown moving through the molten electrolyte. (iii) [1] for layers; [1] for delocalized / mobile electrons. Accept a suitable diagram for M1.
Komentarz
Lithium ions are reduced at the cathode: Li+ + e− → Li. The molten salt contains no water, so the metal is the only possible product at the negative electrode.