Transition Elements

Define complex.

Table 3.1 gives some details of different complexes of $\text{Fe}^{2+}$ and of $\text{Fe}^{3+}$.

Complete Table 3.1.

Table 3.1

Complete Fig. 3.1 to show the splitting of the d-orbitals in a tetrahedral complex.

Explain the reason for the difference in colour of the two complexes $[\text{Fe(H}_2\text{O)}_6]^{3+}$ and $[\text{Fe(H}_2\text{O)}_5\text{SCN}]^{2+}$.

Write an expression for $K_{\text{stab}}$ of $[\text{Fe(H}_2\text{O)}_5\text{SCN}]^{2+}$.

Use information in Table 3.2 to calculate the value of the equilibrium constant, $K_c$, for the following reaction.

A few drops of KF(aq) are added to a solution of $[\text{Fe(H}_2\text{O)}_6]^{3+}(aq)$, followed by a few drops of KSCN(aq).

Use information in Table 3.2 to describe any observations after each addition. Explain your answer.

Write half equations for the oxidation of $\text{C}_2\text{O}_4^{2-}$ ions and for the reduction of $\text{MnO}_4^-$ ions.

• oxidation of $\text{C}_2\text{O}_4^{2-}$

• reduction of $\text{MnO}_4^-$

A student prepares a solution containing 0.100 g of J.

The student titrates this solution with $0.0200\text{ mol dm}^{-3}$ acidified $\text{KMnO}_4(aq)$. The titre obtained is $12.20\text{ cm}^3$.

Assume all of the $\text{C}_2\text{O}_4^{2-}$ ions are oxidised.

Calculate the value of $x$ in $\text{K}_3\text{Fe(C}_2\text{O}_4)_3 \cdot x\text{H}_2\text{O}$.

Give your answer to the nearest whole number. Show your working.

[$M_r$: $\text{K}_3\text{Fe(C}_2\text{O}_4)_3$, 437.1]

Complex ion A contains one $\text{Fe}^{3+}$ ion and six $\text{CN}^-$ ligands.

Complex ion B contains one $\text{Fe}^{2+}$ ion and six $\text{CN}^-$ ligands.

State the formulae of these two complex ions. Include the overall charge of each complex ion.

complex ion A .................................................

complex ion B .................................................

Explain why a solution containing complex ion A and a solution containing complex ion B are different colours.

In complex ion A, the carbon atom of each $\text{CN}^-$ ligand bonds to the $\text{Fe}^{3+}$ ion.

State the type of bonding involved.

Complex ions have different geometries.

Complex ion A is octahedral.

$\text{Ag}^+$ ions form a linear complex with ammonia.

Ni atoms form a tetrahedral complex with carbon monoxide molecules. The carbon atom in the monodentate carbon monoxide ligand bonds to the nickel atom.

$\text{Pd}^{2+}$ ions form a square planar complex with chloride ions.

Complete Fig. 6.1 to show the geometry of each of these four ions, using three-dimensional bonds where necessary. Label one bond angle on each complex ion.

Complex ion A contains one $\text{Fe}^{3+}$ ion and six $\text{CN}^-$ ligands.

Complex ion B contains one $\text{Fe}^{2+}$ ion and six $\text{CN}^-$ ligands.

State the formulae of these two complex ions. Include the overall charge of each complex ion.

complex ion A .................................................

complex ion B .................................................

Explain why a solution containing complex ion A and a solution containing complex ion B are different colours.

In complex ion A, the carbon atom of each $\text{CN}^-$ ligand bonds to the $\text{Fe}^{3+}$ ion.

State the type of bonding involved.

Complex ions have different geometries.

Complex ion A is octahedral.

$\text{Ag}^+$ ions form a linear complex with ammonia.

Ni atoms form a tetrahedral complex with carbon monoxide molecules. The carbon atom in the monodentate carbon monoxide ligand bonds to the nickel atom.

$\text{Pd}^{2+}$ ions form a square planar complex with chloride ions.

Complete Fig. 6.1 to show the geometry of each of these four ions, using three-dimensional bonds where necessary. Label one bond angle on each complex ion.

Copper shows typical properties of transition elements, including its behaviour as a catalyst.

Complete Table 5.1 to show the total number of unpaired electrons in the 3d and 4s orbitals of an isolated gaseous Cu atom and a $\text{Cu}^{2+}$ ion.

The 3d orbitals in an isolated $\text{Cu}^{2+}$ ion are degenerate.

Complete the diagram to show the relative energies of the 3d orbitals in an isolated $\text{Cu}^{2+}$ ion and in $\text{Cu}^{2+}$ in a tetrahedral complex.

Explain why transition elements behave as catalysts.

$\text{CN}^-$ is a monodentate ligand.

Table 5.2 shows information about two complex ions that contain only $\text{CN}^-$ ions as ligands.

Complete Table 5.2.

The complex ion $[\text{Au(CN)}_2\text{Br}_2]^-$ displays geometrical (cis/trans) isomerism.

Draw the structure of trans-$[\text{Au(CN)}_2\text{Br}_2]^-$. State its shape and the Br-Au-Br bond angle.

Calculate the percentage by mass of vanadium in the $0.250\text{ g}$ of impure sample. Assume the impurities do not contain any vanadium ions.

Show your working.

Complete the equation for the reaction between acidified $\text{VO}_3^-$ ions and Zn metal.

Give the formula and charge of the tetrahedral complex formed by $\text{Ni}$ atoms with carbon monoxide molecules. Carbon monoxide is a monodentate ligand. This is complex E.

E = ...............................................................................................................................

Give the formula and charge of the octahedral complex formed by $\text{Ni}^{2+}$ ions with ethanedioate ions. This is complex F.

F = ...............................................................................................................................

Identify which complex, E or F, exists as a mixture of two stereoisomers and the type of stereoisomerism involved.

The complex which exists as a mixture of two stereoisomers is .............................. .

The type of stereoisomerism involved is .............................. .

Explain, by reference to its structure, why $\text{CH}_3\text{NH}_2$ acts as a monodentate ligand.

Some $\text{Cd}^{2+}\text{(aq)}$ is added to a solution containing equal concentrations of $\text{CH}_3\text{NH}_2$ and en.

Predict which of the two complexes in Table 6.1 forms at the higher concentration.

Explain your answer.

complex that forms at the higher concentration ................................................................

explanation ........................................................................................................................

Complete the expression for the $K_{stab}$ of $[\text{Cd(CH}_3\text{NH}_2)_4]^{2+}$.

$K_{stab}$ =

Copper shows typical properties of transition elements, including its behaviour as a catalyst.

Complete Table 5.1 to show the total number of unpaired electrons in the 3d and 4s orbitals of an isolated gaseous Cu atom and a $\text{Cu}^{2+}$ ion.

Table 5.1

The 3d orbitals in an isolated $\text{Cu}^{2+}$ ion are degenerate.

Complete the diagram to show the relative energies of the 3d orbitals in an isolated $\text{Cu}^{2+}$ ion and in $\text{Cu}^{2+}$ in a tetrahedral complex.

Explain why transition elements behave as catalysts.

$\text{CN}^-$ is a monodentate ligand.

Table 5.2 shows information about two complex ions that contain only $\text{CN}^-$ ions as ligands.

Complete Table 5.2.

Table 5.2

The complex ion $[\text{Au}(\text{CN})_2\text{Br}_2]^-$ displays geometrical (cis/trans) isomerism.

Draw the structure of trans-$[\text{Au}(\text{CN})_2\text{Br}_2]^-$. State its shape and the Br-Au-Br bond angle.

Calculate the percentage by mass of vanadium in the $0.250 \text{ g}$ of impure sample.

Assume the impurities do not contain any vanadium ions.

Show your working.

Complete the equation for the reaction between acidified $\text{VO}_3^-$ ions and Zn metal.

Define a transition element.

Define the term degenerate.

Complete the electronic configuration of $\text{Cu}^{2+}$.

$1\text{s}^2$ ...............................................................................................................................

State the colours of the aqueous solutions for the two copper(II) complex ions shown.

• $[\text{Cu}(\text{NH}_3)_4(\text{H}_2\text{O})_2]^{2+}(\text{aq})$ .............................................................................................
• $[\text{CuCl}_4]^{2-}(\text{aq})$ .............................................................................................................

Explain why aqueous complex ions of transition elements are usually coloured.

When an excess of $\text{NH}_3(\text{aq})$ is added to a solution of $[\text{CuCl}_4]^{2-}(\text{aq})$, $[\text{Cu}(\text{NH}_3)_4(\text{H}_2\text{O})_2]^{2+}(\text{aq})$ is formed.

State the type of reaction.
Complete the equation for this reaction. State symbols are not required.

type of reaction ..................................................................................................................

equation

$[\text{CuCl}_4]^{2-} +$ ..................................... $\rightarrow [\text{Cu}(\text{NH}_3)_4(\text{H}_2\text{O})_2]^{2+} +$ .....................................

The $[\text{Cu}(\text{NH}_3)_4(\text{H}_2\text{O})_2]^{2+}$ complex ion shows stereoisomerism.

Complete the three-dimensional diagrams in Fig. 1.1 to show the two different stereoisomers of $[\text{Cu}(\text{NH}_3)_4(\text{H}_2\text{O})_2]^{2+}$.

Deduce which stereoisomer in (d)(ii) is polar.

Explain your answer.

polar isomer ......................................................................................................................

explanation ........................................................................................................................

Suggest how $\mathbf{P}$ can form three dative covalent bonds.

$2$ moles of dianion $\mathbf{P}$, $\text{C}_4\text{H}_5\text{NO}_4^{2-}$, react with $1$ mole of aqueous cobalt(III) ions, $[\text{Co}(\text{H}_2\text{O})_6]^{3+}$ to form $1$ mole of complex ion $\mathbf{Q}$.

Deduce the formula and charge of $\mathbf{Q}$.

Define the stability constant of a complex.

Use the information in Table 1.1 to identify the most stable silver(I) complex.

Explain your answer.

most stable ........................................................................................................................

explanation ........................................................................................................................

Sodium sulfite, $\text{Na}_2\text{SO}_3$, is used as a food preservative.

A $3.75\text{ g}$ sample of impure $\text{Na}_2\text{SO}_3$ is dissolved in distilled water and made up to $250\text{ cm}^3$ in a volumetric flask.

$10.0\text{ cm}^3$ of this solution requires $18.70\text{ cm}^3$ of acidified $0.0150\text{ mol dm}^{-3}$ $\text{MnO}_4^-(\text{aq})$ to reach the end-point.

The equation for the reaction is shown.

Calculate the percentage by mass of $\text{Na}_2\text{SO}_3$ in the sample.

Explain why iron has variable oxidation states.

Complete the shorthand electronic configurations of $\text{Fe}$ and $\text{Fe}^{3+}$.

Define complex.

State the coordination number of $\text{Fe}$ in $[\text{Fe}(\text{H}_2\text{O})_6]^{3+}$.

The H—O—H bond angle in water is $104.5^\circ$.

Suggest the H—O—H bond angle in $[\text{Fe}(\text{H}_2\text{O})_6]^{3+}$.

Explain your answer.

Explain why iron complexes are coloured.

Aqueous solutions of complexes $[\text{Fe}(\text{H}_2\text{O})_6]^{3+}$ and $[\text{Fe}(\text{H}_2\text{O})_5\text{SCN}]^{2+}$ are different colours.

Explain why these complexes are different colours.

$[\text{Fe}(\text{H}_2\text{O})_5(\text{H}_2\text{PO}_4)]^{2+}$ can form when $\text{H}_3\text{PO}_4$ reacts with $[\text{Fe}(\text{H}_2\text{O})_6]^{3+}$.

Write an equation for this reaction.

Write an expression for $K_{\text{stab}}$ of $[\text{Fe}(\text{H}_2\text{O})_5\text{SCN}]^{2+}$ and give its units.

Use the stability constant data in Table 3.1 to calculate the value of the equilibrium constant, $K_{\text{c}}$, for the following equilibrium.

Explain why transition elements have variable oxidation states.

Sketch the shape of a $3\text{d}_{z^2}$ orbital in Fig. 4.1.

Samples of $[\text{Cu}(\text{H}_2\text{O})_6]^{2+}(\text{aq})$ are reacted separately with an excess of solution $\mathbf{A}$ and with an excess of solution $\mathbf{B}$.

The reaction of $[\text{Cu}(\text{H}_2\text{O})_6]^{2+}(\text{aq})$ with solution $\mathbf{A}$ is a precipitation reaction.

The reaction of $[\text{Cu}(\text{H}_2\text{O})_6]^{2+}(\text{aq})$ with solution $\mathbf{B}$ is a ligand substitution reaction.

Suggest a possible identity for solution $\mathbf{A}$ and for solution $\mathbf{B}$. Give relevant observations and the formula of the copper-containing product for each reaction.

solution $\mathbf{A}$ ..................................................................................................................

observations .............................................................................................................................

formula of the copper-containing product .................................................................................

solution $\mathbf{B}$ ..................................................................................................................

observations .............................................................................................................................

formula of the copper-containing product .................................................................................

Solutions containing the $[\text{Ag}(\text{NH}_3)_2]^+$ complex are colourless.

Explain why this complex is colourless.

Two bidentate ligands are shown in Fig. 4.2.

Explain what is meant by a bidentate ligand.

Complete the three-dimensional diagrams in Fig. 4.3 to show the three different stereoisomers of $[\text{Ru}(\text{dpys})_2\text{Cl}_2]^+$.

The dpys ligand can be represented using

State the different types of stereoisomerism shown by $[\text{Ru}(\text{dpys})_2\text{Cl}_2]^+$.

Deduce which stereoisomers in (e)(i) are non-polar. Explain your answer.

Label one bond angle on each of complexes $\mathbf{P}$, $\mathbf{Q}$, $\mathbf{R}$ and $\mathbf{S}$, and identify the size of the angle in degrees.

Identify the shapes of complexes $\mathbf{P}$, $\mathbf{Q}$, $\mathbf{R}$ and $\mathbf{S}$.

$\mathbf{P}$ ...............................................................................................................................................

$\mathbf{Q}$ ...............................................................................................................................................

$\mathbf{R}$ ...............................................................................................................................................

$\mathbf{S}$ ...............................................................................................................................................

Two $\mathbf{L}$ ligands are exchanged with two different monodentate ligands $\mathbf{X}$ and $\mathbf{Y}$ in each of complexes $\mathbf{P}$, $\mathbf{Q}$, $\mathbf{R}$ and $\mathbf{S}$.

Identify all the complexes which form new complexes that show geometrical isomerism.

Three $\mathbf{L}$ ligands are exchanged with three different monodentate ligands $\mathbf{X}$, $\mathbf{Y}$ and $\mathbf{Z}$ in each of complexes $\mathbf{P}$, $\mathbf{Q}$ and $\mathbf{R}$.

Identify all the complexes which form new complexes that show optical isomerism.