Date | November 2018 | Marks available | 1 | Reference code | 18N.2.sl.TZ0.3 |
Level | SL | Paper | 2 | Time zone | TZ0 |
Command term | Sketch | Question number | 3 | Adapted from | N/A |
Question
Bromine can form the bromate(V) ion, BrO3−.
State the electron configuration of a bromine atom.
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.
Draw the Lewis (electron dot) structure for BrO3− that obeys the octet rule.
Predict, using the VSEPR theory, the geometry of the BrO3− ion and the O−Br−O bond angles.
Bromate(V) ions act as oxidizing agents in acidic conditions to form bromide ions.
Deduce the half-equation for this reduction reaction.
Bromate(V) ions oxidize iron(II) ions, Fe2+, to iron(III) ions, Fe3+.
Deduce the equation for this redox reaction.
Markscheme
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
OR
[Ar] 4s2 3d10 4p5 ✔
Accept 3d before 4s.
Accept double-headed arrows.
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.
BrO3− (aq) + 6Fe2+ (aq) + 6H+ (aq) → Br− (aq) + 3H2O (l) + 6Fe3+ (aq) ✔