CAIE A-Level Chemistry 28.2 Chemical Properties of Transition Elements

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

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 complexes 28.2.2—Terms: ligand as a species that contains 28.2.3—Terms 28.2.4—Complex ions 28.2.5—Shapes of transition metal complexes 28.2.6—Coordination number and complex formula 28.2.7—Ligand exchange reactions 28.2.8—Predict, using E 28.2.9—Transition metal redox calculations 28.2.10—Calculations: other redox systems

[Maximum number: 4]

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

(a)

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

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

Fig. 3.1

[ 4 ]

(i)

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

[ 1 ]

(ii)

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

[ 1 ]

$\begin{aligned} \mathrm{TiO}_{2}+6 \mathrm{HF} \rightarrow \mathrm{TiF}_{6}{ }^{2-}+2 \mathrm{H}_{2} \mathrm{O}+2 \mathrm{H}^{+} \mathrm{OR} \mathrm{TiO}_{2}+6 \mathrm{HF} \rightarrow \mathrm{TiF}_{6}{ }^{2-}+2 \mathrm{H}_{3} \mathrm{O}^{+} \end{aligned}$

(iii)

State what is meant by bidentate ligand.

[ 2 ]

[Maximum number: 4]

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

(a)

Two different complex ions, X and Y, can form when anhydrous $\mathrm{RuCl}_{3}$ reacts with water under certain conditions.
X and Y have octahedral geometry.
Aqueous samples of X and Y react separately with an excess of $\mathrm{AgNO}_{3}(\mathrm{aq})$ . 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 ]

(i)

Complete Table 4.1 to suggest formulae for X and Y.

Table 4.1

[ 2 ]

X $\left[\mathrm{Ru}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5} \mathrm{Cl}\right]^{2+}$

Y $\left[\mathrm{Ru}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4} \mathrm{C}_{2}\right]^{+} \quad$ ECF [1] if reversed

(b)

Fig. 4.1 shows another ruthenium complex.

Fig. 4.1

This complex contains the neutral ligand pyrazine.

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

[ 1 ]

(i)

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

[ 1 ]

(c)

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

$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 ]

(i)

Suggest a reagent for step 1.

[ 1 ]

$\mathrm{SOCl}_{2}$ OR $\mathrm{PCl}_{3}$ OR $\mathrm{PCl}_{5}$

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Covered syllabus points

28.2 Chemical properties of first-row transition elements question 1

Question (a)

Question (i)

Question (ii)

Question (iii)

28.2 Chemical properties of first-row transition elements question 2

Question (a)

Question (i)

Question (b)

Question (i)

Question (c)

Question (i)