Zadanie 4b
Wzorowane na: Chemistry HL Paper 2, May 2024, TZ1, pytanie 4(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 4a-4b.
Carbonyl chloride (phosgene), COCl2, is made industrially from carbon monoxide and chlorine over a charcoal catalyst:
CO(g) + Cl2(g) → COCl2(g) ΔH = −108 kJ mol−1
Polecenie
(i) Draw the Lewis (electron dot) structure of carbonyl chloride.
(ii) Mark the bond polarities on your Lewis structure using the symbols δ+ and δ−.
(iii) Explain the shape of the carbonyl chloride molecule and whether it is polar.
(iv) State the hybridization of carbon in CO and in COCl2.
(v) State how many σ bonds and how many π bonds one molecule of carbonyl chloride contains.
(vi) Determine the bond enthalpy of carbon monoxide, in kJ mol−1. Use section 12 of the data booklet and the enthalpy change given in the stem; assume that the carbon-oxygen bond in carbonyl chloride is a double bond.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) carbon in the centre joined to oxygen by a double bond and to two chlorine atoms by single bonds; two lone pairs on oxygen and three lone pairs on each chlorine ✔
(ii) δ+ on carbon AND δ− on oxygen AND δ− on each chlorine ✔
(iii) trigonal planar AND three electron domains repel each other «to a maximum separation» ✔
polar AND bond dipoles do not cancel / asymmetric distribution of charge ✔
(iv) carbon monoxide: sp AND carbonyl chloride: sp2 ✔
(v) three σ AND one π ✔
(vi) x + 242 − [804 + 2(324)] = −108 ✔
x = −108 − 242 + 804 + 648 = 1102 «kJ mol−1» ✔
Schemat punktowania
(i) [1]; dots, crosses and lines are all acceptable in any combination; the shape of the drawing is not marked. (ii) [1]; accept only one correct δ+ and δ− pair. (iii) Award [1] for "trigonal planar and polar" without correct explanations. (iv) [1] for both. (v) [1] for both. (vi) Award [2] for the correct final answer; M1 for the correct bond enthalpies set into the equation (C=O 804, C-Cl 324, Cl-Cl 242), M2 for the value.
Komentarz
The result (1102) differs from the data booklet value for the triple bond in CO (1077) because booklet values are averages over many compounds, while here the value is derived from one measured reaction enthalpy and two other average bond enthalpies; accept 1100 within rounding.