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Date	November 2018	Marks available	1	Reference code	18N.2.sl.TZ0.3
Level	SL	Paper	2	Time zone	TZ0
Command term	Draw	Question number	3	Adapted from	N/A

Question

Bromine can form the bromate(V) ion, BrO₃⁻.

State the electron configuration of a bromine atom.

[1]

a.i.

Sketch the orbital diagram of the valence shell of a bromine atom (ground state) on the energy axis provided. Use boxes to represent orbitals and arrows to represent electrons.

[1]

a.ii.

Draw the Lewis (electron dot) structure for BrO₃⁻ that obeys the octet rule.

[1]

Predict, using the VSEPR theory, the geometry of the BrO₃⁻ ion and the O−Br−O bond angles.

[3]

Bromate(V) ions act as oxidizing agents in acidic conditions to form bromide ions.

Deduce the half-equation for this reduction reaction.

[2]

d.i.

Bromate(V) ions oxidize iron(II) ions, Fe²⁺, to iron(III) ions, Fe³⁺.

Deduce the equation for this redox reaction.

[1]

d.ii.

Markscheme

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵

[Ar] 4s² 3d¹⁰ 4p⁵ ✔

Accept 3d before 4s.

a.i.

Accept double-headed arrows.

a.ii.

Accept dots, crosses or lines to represent electron pairs.

Geometry:
trigonal/pyramidal ✔

Reason:
three bonds AND one lone pair
OR
four electron domains ✔

O−Br−O angle:
107° ✔

Accept “charge centres” for “electron domains”.

Accept answers in the range 104–109°.

BrO₃⁻ (aq) + 6e⁻ + 6H⁺ (aq) → Br⁻ (aq) + 3H₂O (l)

correct reactants and products ✔

balanced equation ✔

Accept reversible arrows.

d.i.

BrO₃⁻ (aq) + 6Fe²⁺ (aq) + 6H⁺ (aq) → Br⁻ (aq) + 3H₂O (l) + 6Fe³⁺ (aq) ✔

d.ii.

Examiners report

[N/A]

a.i.

[N/A]

a.ii.

[N/A]

d.i.

[N/A]

d.ii.

Syllabus sections

Core » Topic 4: Chemical bonding and structure » 4.3 Covalent structures

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