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CAIE A-Level Chemistry A2 28.2 Chemical Properties of First Row Transition Elements Questions

Practise ligand definitions, complex geometry, ligand exchange, precipitation and redox reactions of first-row ions.

Syllabus
2028–2030
Course
Chemistry 9701
Level
A2

Exam points

  • identify ligands, denticity and coordination number from the number of donated lone pairs and bonds
  • write ligand-exchange or hydroxide-deprotonation equations and predict formulae and colours
  • distinguish precipitation, ligand exchange and redox when interpreting Cu2+ or Co2+ observations

Covered syllabus points

28.2.1—Ligand reactions forming complexes28.2.2—Terms: ligand as a species that contains28.2.3—Terms28.2.4—Complex ions28.2.5—Shapes of transition metal complexes28.2.6—Coordination number and complex formula28.2.7—Ligand exchange reactions28.2.8—Predict, using E28.2.9—Transition metal redox calculations28.2.10—Calculations: other redox systems

Question 1

[Maximum number: 4]

Titanium is a transition element in Period 4. It is commonly found as TiO2\mathrm{TiO}_{2} in minerals.

Question (a)

(a)

Some reactions of TiO2\mathrm{TiO}_{2} are shown in Fig. 3.1.

The anion, acac −^{-}, is a bidentate ligand.

Fig. 3.1

Fig. 3.1

[ 4 ]

Question (i)

(i)

The titanium ions in TiF62−\mathrm{TiF}_{6}{ }^{2-} and Ti(acac)2Cl2\mathrm{Ti}(\mathrm{acac})_{2} \mathrm{Cl}_{2} have a coordination number of 6 . State what is meant by coordination number.

[ 1 ]

Question (ii)

(ii)

Write an equation for the formation of TiF62−\mathrm{TiF}_{6}{ }^{2-} from TiO2\mathrm{TiO}_{2}.

[ 1 ]

Question (iii)

(iii)

State what is meant by bidentate ligand.

[ 2 ]

Question 2

[Maximum number: 4]

Ruthenium and osmium are transition metals below iron in Group 8 of the Periodic Table.

Question (a)

(a)

Two different complex ions, X and Y, can form when anhydrous RuCl3\mathrm{RuCl}_{3} reacts with water under certain conditions.
X and Y have octahedral geometry.
Aqueous samples of X and Y react separately with an excess of AgNO3(aq)\mathrm{AgNO}_{3}(\mathrm{aq}). Different amounts of AgClare precipitated:
- 1 mole of complex ion X produces 2 moles of AgCl
- 1 mole of complex ion Y produces 1 mole of AgCl.

[ 2 ]

Question (i)

(i)

Complete Table 4.1 to suggest formulae for X and Y.

Table 4.1

Table 4.1

[ 2 ]

Question (b)

(b)

Fig. 4.1 shows another ruthenium complex.

Fig. 4.1

Fig. 4.1

This complex contains the neutral ligand pyrazine.

Figure for Question (b) — CAIE A-Level Chemistry A2
[ 1 ]

Question (i)

(i)

Suggest how pyrazine is able to bond to two separate ruthenium ions.

[ 1 ]

Question (c)

(c)

Osmium tetroxide, OsO4\mathrm{OsO}_{4}, reacts with alkenes in a similar manner to cold dilute acidified MnO4−\mathrm{MnO}_{4}{ }^{-}.

Fig. 4.2 shows a proposed synthesis of a condensation polymer \(\mathbf{G

Fig. 4.2 shows a proposed synthesis of a condensation polymer \(\mathbf{G

[ 1 ]

Question (i)

(i)

Suggest a reagent for step 1.

[ 1 ]
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