Question 18N.2.hl.TZ0.3
| Date | November 2018 | Marks available | [Maximum mark: 16] | Reference code | 18N.2.hl.TZ0.3 |
| Level | hl | Paper | 2 | Time zone | TZ0 |
| Command term | Calculate, Deduce, Determine, Draw, Predict, Sketch, State, State and explain | Question number | 3 | Adapted from | N/A |
Bromine can form the bromate(V) ion, BrO3−.
State the electron configuration of a bromine atom.
[1]
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
OR
[Ar] 4s2 3d10 4p5 ✔
Accept 3d before 4s.
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]
Accept double-headed arrows.
Draw two Lewis (electron dot) structures for BrO3−.
[2]
Structure I - follows octet rule:
Structure II - does not follow octet rule:
Accept dots, crosses or lines to represent electron pairs.
Determine the preferred Lewis structure based on the formal charge on the bromine atom, giving your reasons.
[2]
«structure I» formal charge on Br = +2
OR
«structure II» formal charge on Br = 0/+1 ✔
structure II is preferred AND it produces formal charge closer to 0 ✔
Ignore any reference to formal charge on oxygen.
Predict, using the VSEPR theory, the geometry of the BrO3− ion and the O−Br−O bond angles.
[3]
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°.
Bromate(V) ions act as oxidizing agents in acidic conditions to form bromide ions.
Deduce the half-equation for this reduction reaction.
[2]
BrO3− (aq) + 6e− + 6H+ (aq) → Br− (aq) + 3H2O (l)
correct reactants and products ✔
balanced equation ✔
Accept reversible arrows.
Bromate(V) ions oxidize iron(II) ions, Fe2+, to iron(III) ions, Fe3+.
Deduce the equation for this redox reaction.
[1]
BrO3− (aq) + 6Fe2+ (aq) + 6H+ (aq) → Br− (aq) + 3H2O (l) + 6Fe3+ (aq) ✔
Calculate the standard Gibbs free energy change, ΔGΘ, in J, of the redox reaction in (ii), using sections 1 and 24 of the data booklet.
EΘ (BrO3− / Br−) = +1.44 V
[2]
EΘreaction = «+1.44 V – 0.77 V =» 0.67 «V» ✔
ΔGΘ = «–nFEΘreaction = – 6 × 96500 C mol–1 × 0.67 V =» –3.9 × 105 «J» ✔
State and explain the magnetic property of iron(II) and iron(III) ions.
[2]
both are paramagnetic ✔
«both» contain unpaired electrons ✔
Accept orbital diagrams for both ions showing unpaired electrons.