| Date | November 2018 | Marks available | 2 | Reference code | 18N.2.hl.TZ0.3 |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | State and explain | 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 two Lewis (electron dot) structures for BrO3−.
Determine the preferred Lewis structure based on the formal charge on the bromine atom, giving your reasons.
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.
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
State and explain the magnetic property of iron(II) and iron(III) ions.
Markscheme
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
OR
[Ar] 4s2 3d10 4p5 ✔
Accept 3d before 4s.
Accept double-headed arrows.
Structure I - follows octet rule:
Structure II - does not follow octet rule:
Accept dots, crosses or lines to represent electron pairs.
«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.
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) ✔
EΘreaction = «+1.44 V – 0.77 V =» 0.67 «V» ✔
ΔGΘ = «–nFEΘreaction = – 6 × 96500 C mol–1 × 0.67 V =» –3.9 × 105 «J» ✔
both are paramagnetic ✔
«both» contain unpaired electrons ✔
Accept orbital diagrams for both ions showing unpaired electrons.
Examiners report
Syllabus sections
- 22M.1.hl.TZ2.7: Which of these ions are likely to be paramagnetic? I. Ti3+II. Cr3+III. Fe3+ A. I and II...
-
18M.2.hl.TZ2.3d:
Explain why transition metals exhibit variable oxidation states in contrast to alkali metals.
-
18M.2.hl.TZ1.1h:
Describe the bond formation when urea acts as a ligand in a transition metal complex ion.
-
17M.2.hl.TZ1.4d:
Suggest why experiments involving tetracarbonylnickel are very hazardous.
-
18N.1.hl.TZ0.8:
Which is correct for the complex ion in [Fe(H2O)5Cl]SO4?
-
17M.1.hl.TZ1.8:
What is the charge on the iron(III) complex ion in [Fe(OH)2(H2O)4]Br?
A. 0
B. 1+
C. 2+
D. 3+
-
19M.1.hl.TZ1.8:
Which electrons are removed from iron (Z = 26) to form iron(II)?
A. two 3d electrons
B. two 4s electrons
C. one 4s electron and one 3d electron
D. two 4p electrons
-
19M.1.hl.TZ2.8:
What is the oxidation state of the metal ion and charge of the complex ion in [Co(NH3)4Cl2]Cl?
- 17N.2.hl.TZ0.3d.ii: Deduce the charge on the complex ion and the oxidation state of cobalt.
-
17M.2.hl.TZ2.2b.iii:
Explain why iron forms many different coloured complex ions.
- 16N.2.hl.TZ0.2f: Explain how ethanedioate ions act as ligands.
- 17N.2.hl.TZ0.3e: Describe, in terms of acid-base theories, the type of reaction that takes place between the...
- 17N.2.hl.TZ0.3d.i: State the shape of the complex ion.
-
17M.2.hl.TZ1.2e:
Describe, in terms of the electrons involved, how the bond between a ligand and a central metal ion is formed.
-
17M.2.hl.TZ1.4a:
Formulate an equation for the oxidation of nickel(II) sulfide to nickel(II) oxide.
-
22M.2.hl.TZ1.4e:
Mg(OH)+ is a complex ion, but Mg is not regarded as a transition metal. Contrast Mg with manganese, Mn, in terms of one characteristic chemical property of transition metals, other than complex ion formation.
-
19M.2.hl.TZ2.4b(iii):
Predict two other chemical properties you would expect rhenium to have, given its position in the periodic table.
-
17M.1.hl.TZ2.8:
Ammonia is a stronger ligand than water. Which is correct when concentrated aqueous ammonia solution is added to dilute aqueous copper(II) sulfate solution?
A. The d-orbitals in the copper ion split.
B. There is a smaller splitting of the d-orbitals.
C. Ammonia replaces water as a ligand.
D. The colour of the solution fades.
-
17M.2.hl.TZ1.4b:
The nickel obtained from another ore, nickeliferous limonite, is contaminated with iron. Both nickel and iron react with carbon monoxide gas to form gaseous complexes, tetracarbonylnickel, , and pentacarbonyliron, . Suggest why the nickel can be separated from the iron successfully using carbon monoxide.
-
21M.1.hl.TZ1.9:
What is the overall charge, , of the chromium (III) complex?
A. 0
B. 1+
C. 2−
D. 3+
-
20N.1.hl.TZ0.8:
Which of these statements are correct?
I. Zinc is not a transition element.
II. Ligands are Lewis bases.
III. Manganese(II) chloride is paramagnetic.A. I and II only
B. I and III only
C. II and III only
D. I, II and III
-
21N.1.hl.TZ0.8:
Which complex ion contains a central ion with an oxidation state of +3?
A. [PtCl6]2−B. [Cu(H2O)4(OH)2]
C. [Ni(NH3)4(H2O)2]2+
D. [Co(NH3)4Cl2]+
