Wzorowane na: Chemistry SL Paper 2, November 2025, TZ3, pytanie 5(c). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Informacja do zadań 5a-5c.
The relative abundances of the two isotopes in a sample of chlorine are shown below.
| Isotope | Relative abundance / % |
|---|---|
| 75.50 |
| 24.50 |
(i) Deduce the condensed electron configuration of chlorine.
(ii) Describe the bonding in a molecule of chlorine in terms of valence electrons.
(iii) Explain why chlorine has a much lower boiling point than bromine, although both exist as simple diatomic molecules.
(iv) Deduce the equation, and the colour change observed, for the reaction of aqueous chlorine with a dilute aqueous bromide solution.
(v) Outline why chlorine does not react with an aqueous fluoride solution.
(vi) Deduce the products of the electrolysis of molten cobalt(II) chloride, .
(i) ✔
(ii) «single» shared pair «of electrons» between the two atoms ✔
(iii) both and are non-polar molecules with «only» London/dispersion forces between molecules ✔
has more electrons «greater molar mass» than
(iv)
colour change: «almost» colourless to orange/yellow ✔
(v) chlorine is a weaker oxidizing agent than fluorine / more difficult to reduce than fluorine ✔
(vi) Product at anode: chlorine /
Product at cathode: cobalt / ✔
(i) [1]; do not accept the full, non-condensed electron configuration. (ii) [1]; do not accept just 'covalent'. (iii) M1: both molecules are non-polar with only London/dispersion forces; M2: bromine has more electrons, so stronger dispersion forces and a higher boiling point. (iv) M1: correct equation; M2: correct colour change; accept a more specific shade of orange/yellow. (v) [1]; accept a valid answer referring to oxidizing power decreasing down group 17, or to E⊖ values; do not accept just 'fluorine is more reactive' with no comparison of oxidizing/reducing power. (vi) [1] for each correct product; award [1 max] for both products correct but assigned to the wrong electrode; do not accept ions.
The direction of a halogen displacement reaction, and the fact that chlorine cannot displace fluoride, both follow from the same trend: oxidizing power falls down group 17, so a halogen higher in the group always displaces a halide ion below it, never the reverse.
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