Zadanie 3c
Wzorowane na: Chemistry SL Paper 3, November 2024, pytanie 3(c). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Polecenie
(i) Bronze, an alloy of copper and tin, is used for ship propellers and bearings. Explain, by referring to its structure, why bronze is less malleable than pure copper.
(ii) In a separate process, zinc is removed from a copper-zinc alloy by reaction with aqueous potassium hydroxide. Deduce the coefficients, using the smallest whole numbers, for the equation below.
(iii) The copper remaining after this treatment is porous. Suggest why this makes it an effective solid catalyst.
(iv) Suggest how scientists could recognize that copper catalyses a reaction before understanding its mechanism.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) tin atoms are a different size from copper atoms «so they distort/disrupt the regular lattice» ✔
layers of atoms cannot slide over each other as easily ✔
(ii) Zn(s) + 2 KOH(aq) + 2 H2O(l) → K2[Zn(OH)4](aq) + H2(g) ✔
(iii) pores provide a large surface area for reactants to contact the catalyst ✔
(iv) experiments show a faster reaction in its presence while the copper is recovered unchanged overall ✔
Schemat punktowania
(i) Two marks as in HL: lattice disruption and hindered sliding. (ii) One mark for 1,2,2,1,1. (iii) One mark for large surface area. (iv) One mark for an observation of increased rate with catalyst unchanged overall; trial and error alone is insufficient.