Zadanie 3c, Paper 2, maj 2026, TZ1, Chemia IB SL
Wzorowane na: Chemistry SL Paper 2, May 2026, TZ1, pytanie 3(c). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
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Zadanie
Wspólne informacje do wiązki zadań
Pentane, CH3CH2CH2CH2CH3, is a common fuel.
Polecenie
Pentan-2-ol can form by reacting pent-1-ene with water in the presence of an acid catalyst.
CH2=CHCH2CH2CH3(g) + H2O(l) → CH3CH(OH)CH2CH2CH3(aq) ΔH⊖ = −84 kJ mol−1
(i) Explain why increasing the temperature would increase the rate of this reaction.
(ii) Explain the relative solubility of pentan-2-ol and pent-1-ene in water.
(iii) Pent-1-ene can also form a polymer. Draw a section of the polymer with three repeating units.
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Odpowiedź z klucza
(i) the frequency of collisions increases «the particles move faster, so more collisions per unit time» ✔
a greater proportion/fraction of the particles has energy ≥ Ea, so a greater proportion of collisions is successful ✔
(ii) pentan-2-ol is more soluble in water than pent-1-ene AND it has an –OH «hydroxyl» group which forms hydrogen bonds with water ✔
pent-1-ene is less soluble/not soluble AND is non-polar/has only London (dispersion) forces ✔
(iii) three repeating units of −CH2−CH(C3H7)− joined by single C–C bonds in one chain, e.g. …CH2−CH(C3H7)−CH2−CH(C3H7)−CH2−CH(C3H7)⋅⋅⋅, with propyl side chains «not methyl», no C=C bonds left and continuation bonds shown at both ends ✔
Schemat punktowania
(i) [2] M1: increased frequency of collisions; a reference to frequency or to time is required, so do not accept "chance" or "probability" without mention of time; M2: increased collision energy, so a greater proportion of collisions are successful, OR a greater fraction of molecules with E ≥ Ea. Do not accept answers about the equilibrium shifting. (ii) [2] M1: pentan-2-ol more soluble AND the –OH (hydroxyl) group forms hydrogen bonds with water; M2: pent-1-ene less/not soluble AND non-polar/only London forces. Do not accept hydroxide for hydroxyl. Award [1] for "pentan-2-ol is polar AND pent-1-ene is non-polar" alone; award [1] for "pentan-2-ol is soluble/more soluble AND pent-1-ene is not/less soluble" alone. (iii) [1] correct repeating unit with the propyl side chain, three units joined, no double bonds, continuation bonds shown; side chains may be drawn on opposite sides or head to tail; ignore square brackets or n; accept a skeletal formula.
Komentarz. The question is about rate, not equilibrium: the negative ΔH⊖ does not matter for part (i).