Zadanie 4e
Wzorowane na: Chemistry HL Paper 2, May 2022, TZ1, pytanie 4(e). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
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Polecenie
Al(OH)2+ is a complex ion, yet aluminium is not classed as a transition metal. Contrast aluminium with chromium, Cr, for one characteristic chemical property of transition metals, apart from the formation of complex ions.
Property:
Comparison:
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Odpowiedź z klucza
Alternative 1
Property: variable oxidation state ✔
Comparison: Cr forms compounds with oxidation states +2, +3 and +6 AND Al is +3 in all its compounds ✔
Alternative 2
Property: coloured ions / compounds / complexes ✔
Comparison: Cr ions / compounds are coloured «for example Cr3+ green, CrO42− yellow» AND Al ions / compounds are colourless / white ✔
Alternative 3
Property: catalytic activity ✔
Comparison: chromium compounds act as catalysts AND aluminium compounds do not «generally» catalyse reactions ✔
Schemat punktowania
M1: a valid property; M2: a correct comparison for both elements. A correct named example may be used for any property. An answer that only cites atomic structure (for instance an incomplete d sublevel) does not earn the marks, although a correct discussion can earn ECF.