Edexcel IAL Chemistry Topic 17 Transition Metals and their Chemistry

Topic 17 questions move from definitions and electron configurations into ligands, complex ions, colour changes, catalysis and transition-metal redox chemistry.

Exam points

Classify transition metals by stable ions with incompletely filled d orbitals.
Deduce Period 4 d-block atom and ion configurations, including Cr and Cu exceptions.
Use ligand, complex-ion and colour evidence to interpret transition-metal reactions.

Covered syllabus points

17.1—Transition metals are d-block elements that form one or more stable ions with incompletely-filled d-orbitals 17.2—Deduce the electronic configurations of atoms and ions of the d-block elements of Period 4 (Sc-Zn) given their atomic number 17.3—Why transition metals show variable oxidation number 17.4—What is meant by the term ‘ligand’17.5—Dative (coordinate) covalent bonding is involved in the formation of complex ions 17.6—A complex ion is a central metal ion surrounded by ligands 17.7—Aqueous solutions of transition metal ions are usually coloured 17.8—The colour of aqueous ions, and other complex ions, is a consequence of the splitting of the energy levels of the d-orbitals 17.9—Why there is a lack of colour in some aqueous ions and other complex ions 17.10—The meaning of the term ‘coordination number’17.11—Colour changes in transition metal ions may arise as a result of changes in: i oxidation number of the ion ii ligand iii 17.12—H2O, OH- and NH3 act as monodentate ligands 17.13—Why complexes with six-fold coordination have an octahedral shape, such as those formed by metal ions with H2O, OH- and NH3 17.14—Transition metal ions may form tetrahedral complexes with relatively large ions such as Cl-17.15—Square planar complexes are also formed by transition metal ions and that cis-platin is an example of such a complex which 17.16—The terms ‘bidentate’ and ‘hexadentate’ in relation to ligands 17.17—Haemoglobin is an iron(II) complex containing a polydentate ligand and that ligand exchange occurs when an oxygen molecule 17.18—The colours of the oxidation states of vanadium (+5, +4, +3 and +2) in its compounds 17.19—Redox reactions for the interconversion of the oxidation states of vanadium (+5, +4, +3 and +2), in terms of the relevant Eo 17.20—Understand, in terms of the relevant E values, that the dichromate(VI) ion, Cr2O2- i can be reduced to Cr3+ and Cr2+ ions 17.21—Dichromate(VI) ions can be converted into chromate(VI) ions through the equilibrium Cr2O7^2− + H2O ⇌ 2CrO4^2− + 2H+17.22—Record observations and write suitable equations for the reactions of Cr3+(aq), Mn2+(aq), Fe2+(aq), Fe3+(aq), Co2+(aq)17.23—Write ionic equations to show the meaning of amphoteric behaviour, deprotonation and ligand exchange in the reactions 17.24—Ligand exchange, and an accompanying colour change, occurs in the formation of: i [Cu(NH3)4(H2O)2]2+ from [Cu(H2O)6]2+ via 17.25—Understand, in terms of the positive increase in ∆Ssystem, that the substitution of a monodentate ligand by a bidentate or 17.26—Transition metals and their compounds can act as heterogeneous and homogeneous catalysts 17.27—A heterogeneous catalyst is in a different phase from the reactants and that the reaction occurs at the surface of 17.28—Understand, in terms of oxidation number, how V2O5 acts as a catalyst in the contact process 17.29—How a catalytic converter decreases carbon monoxide and nitrogen monoxide emissions from internal combustion engines by: i 17.30—A homogeneous catalyst is in the same phase as the reactants and appreciate that the catalysed reaction will proceed via 17.31—The role of Fe2+ ions in catalysing the reaction between I− and S2O8^2− ions 17.32—The role of Mn2+ ions in autocatalysing the reaction between MnO4− and C2O4^2− ions 17.33—CORE PRACTICAL 14 The preparation of a transition metal complex

[Maximum number: 3]

This question is about mercury, Hg, and its compounds.
Mercury is a liquid element in the same group of the Periodic Table as zinc.
The electronic configuration of mercury is $[\mathrm{Xe}] 4 \mathrm{f}^{14} 5 \mathrm{~d}^{10} 6 \mathrm{~s}^{2}$ .

Mercury forms compounds in either the +1 or +2 oxidation states.

Explain why mercury is classified as a d-block element but is not a transition element.
(3)

An explanation that makes reference to the following points:

- $\left(\mathrm{Hg}^{+}\right.$ is $\left.[\mathrm{Xe}] 4 \mathrm{f}^{14}\right) 5 \mathrm{~d}^{10} 6 \mathrm{~s}^{1}$

and $\left(\mathrm{Hg}^{2+}\right.$ is $\left.[\mathrm{Xe}] 4 \mathrm{f}^{14}\right) 5 \mathrm{~d}^{10}\left(6 \mathrm{~s}^{0}\right)$

(1)

- (d-block element as last) electron goes into a (5)d-orbital(s) (when the electronic configuration is written according to the Aufbau principle)

(1)

- (not transition element as) $\mathrm{Hg}^{+}$ and $\mathrm{Hg}^{2+}$ /(stable) ions do not have incompletely filled (5)d-orbital(s)

(1)

Accept use of d-subshell for d-orbital(s) Allow use of d-shell for d-subshell Penalise use of just d-block for d-shell once only Penalise use of 3d/4d for 5d once only

Allow Hg loses (only) its 6s electrons (when forming ions/compounds)

Do not award answer in terms of the electronic configuration of an ion of mercury

Allow $\mathrm{Hg}^{+}$ and $\mathrm{Hg}^{2+}$ /(stable) ions have completely full (5)d-orbital(s) Ignore any reference to d-d transitions / other transition element properties

Do not award answer in terms of the electronic configuration of the element / an Hg atom

(3)

Expert

[Maximum number: 1]

Which d-block elements of Period 3 do not follow the periodic pattern in the electronic configuration of their atoms?

chromium and copper

chromium and manganese

scandium and copper

scandium and zinc

[Maximum number: 6]

This question is about the chemistry of vanadium.
The standard electrode potentials of some vanadium species are shown.

Table for Question Topic 17: Transition Metals and their Chemistry question 3 — Edexcel A-Level Chemistry A2

(a)

Explain the highest stable oxidation state formed by vanadium, by referring to its electronic configuration.

[ 3 ]

(b)

Most vanadium produced is used to make a steel alloy called ferrovanadium. The vanadium content of ferrovanadium may be determined by a titration method.

Procedure
- The sample of ferrovanadium is dissolved in chloric(V) acid.

The vanadium species formed is VO_3^-.
- The resulting solution is transferred to a 250.0 cm^3 volumetric flask, washings added and the solution made up to the mark with distilled water and mixed.
- Using a pipette, 25.0 cm^3 of the solution is transferred to a conical flask and 25.0 cm^3 of a 0.250 mol dm^-3 solution of iron(II) sulfate, FeSO_4, is added.
The iron(II) ions react with the VO_3^-ions:

\mathrm{VO}_{3}^{-}+4 \mathrm{H}^{+}+\mathrm{Fe}^{2+} \rightleftharpoons \mathrm{VO}^{2+}+2 \mathrm{H}_{2} \mathrm{O}+\mathrm{Fe}^{3+}

- The resulting solution is titrated against potassium manganate(VII) to determine the amount of iron(II) ions remaining.

\mathrm{MnO}_{4}^{-}+8 \mathrm{H}^{+}+5 \mathrm{Fe}^{2+} \rightarrow \mathrm{Mn}^{2+}+5 \mathrm{Fe}^{3+}+4 \mathrm{H}_{2} \mathrm{O}

In an experiment, the mass of ferrovanadium used was 4.87 g , the concentration of potassium manganate(VII) was 0.0195 mol dm^-3 and a mean titre of 22.50 cm^3 was obtained.

[ 1 ]

(i)

Give the colour of the solution at the end-point of the titration.

[ 1 ]

(c)

In the manufacture of sulfuric acid, vanadium(V) oxide, V_2 O_5, is the catalyst used in the conversion of sulfur dioxide to sulfur trioxide:

2 \mathrm{SO}_{2}+\mathrm{O}_{2} \rightleftharpoons 2 \mathrm{SO}_{3}

Write two equations to show a possible mechanism for this reaction.
State symbols are not required.

[ 2 ]

All question bank results loaded

Covered syllabus points

Topic 17: Transition Metals and their Chemistry question 1

Topic 17: Transition Metals and their Chemistry question 2

Topic 17: Transition Metals and their Chemistry question 3

Question (a)

Question (b)

Question (i)

Question (c)