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Question 18N.2.sl.TZ0.3

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Date November 2018 Marks available [Maximum mark: 9] Reference code 18N.2.sl.TZ0.3
Level sl Paper 2 Time zone TZ0
Command term Deduce, Draw, Predict, Sketch, State Question number 3 Adapted from N/A
3.
[Maximum mark: 9]
18N.2.sl.TZ0.3

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

(a.i)

State the electron configuration of a bromine atom.

[1]

Markscheme

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5

OR

[Ar] 4s2 3d10 4p5 ✔

 

Accept 3d before 4s.

(a.ii)

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]

Markscheme

Accept double-headed arrows.

(b)

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

[1]

Markscheme

Accept dots, crosses or lines to represent electron pairs.

(c)

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

[3]

Markscheme

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°.

(d.i)

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

Deduce the half-equation for this reduction reaction.

[2]

Markscheme

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

correct reactants and products ✔

balanced equation ✔

 

Accept reversible arrows.

(d.ii)

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

Deduce the equation for this redox reaction.

[1]

Markscheme

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

 

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