transition map

Here is a comprehensive and rigorously structured Obsidian Markdown file containing all question permutations for the Cambridge A Level Chemistry (9701) topic 28. Chemistry of the transition elements.

It includes exact past-paper questions, variations of those questions, and potential questions derived directly from the syllabus learning outcomes. The questions are formatted as requested using Obsidian [!info] callouts, with the maximum observed/expected marks in parentheses.

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Topic 28: Chemistry of the Transition Elements

28.1 General Physical and Chemical Properties

Definition of a Transition Element (2 marks)

Define a transition element.

Electronic Configurations of Atoms and Ions (2 marks)

Complete the electronic configuration for an isolated gaseous copper atom, Cu, and a copper(II) ion, .

Typical Chemical Properties (2 marks)

Transition elements such as iron and copper exhibit specific chemical properties not seen in s-block elements. State two typical chemical properties of a transition element.

Shape of d-orbitals (2 marks)

There are five different 3d orbitals. Sketch the shapes of a orbital and a orbital on the axes provided.

Variable Oxidation States (2 marks)

Explain why transition elements have variable oxidation states in their compounds, whereas s-block elements such as calcium do not.

Complex Ion Formation (2 marks)

Explain, in terms of d-orbitals, why transition elements are able to form complex ions.

Catalytic Behaviour (2 marks)

Explain why transition elements and their compounds behave as catalysts.

Modes of Action of Catalysts (3 marks)

Iron acts as a heterogeneous catalyst in the Haber process, whereas ions act as a homogeneous catalyst in the reaction between and .

1. Explain the difference between a homogeneous catalyst and a heterogeneous catalyst.
2. Describe the mode of action of a heterogeneous iron catalyst.

Homogeneous Catalysis Equations (2 marks)

Write equations for the two reactions that occur when is added to a mixture of and to act as a homogeneous catalyst.

28.2 Characteristic Chemistry and Ligands

Definition of a Ligand (2 marks)

Explain what is meant by the term ligand in the context of transition element chemistry.

Classification of Ligands (2 marks)

Explain what is meant by the terms monodentate, bidentate, and polydentate ligand.

Identifying Ligand Donation (2 marks)

1,2-diaminoethane (en) and ethanedioate () are bidentate ligands. is a polydentate ligand. Deduce the number of lone pairs donated by each ligand in a single complex ion.

Definition of a Complex (1 mark)

Define the term complex (or complex ion).

Definition of Coordination Number (1 mark)

State what is meant by the coordination number of a transition metal complex.

Deducing Geometry and Bond Angles (4 marks)

Complete the table to state the geometry (shape) and bond angles for the following complex ions:

Deducing Complex Formulae and Charge (2 marks)

Ruthenium(III) ions, , form an octahedral complex with phenanthroline (, a neutral bidentate ligand) and chloride ions. The complex ion contains two phenanthroline molecules. Deduce the formula and overall charge of this complex ion.

Copper(II) Aqueous Reactions: Precipitation vs Ligand Exchange (6 marks)

Aqueous copper(II) sulfate contains the complex ion.

1. Describe what is observed when a few drops of aqueous ammonia are added to this solution. Write an ionic equation for this reaction.
2. Describe what is observed when an excess of aqueous ammonia is added. Write an ionic equation for this ligand exchange reaction.
3. Describe what is observed when an excess of concentrated is added. Write the equation and state the geometry of the product.

Cobalt(II) Aqueous Reactions (6 marks)

An aqueous solution of cobalt(II) chloride contains and is pink. State the reagents, the colour of the products, and write the ionic equations when: 4. Aqueous sodium hydroxide is added. 5. An excess of concentrated hydrochloric acid is added.

Redox Reactions: Manganate(VII) and Ethanedioate (4 marks)

Ethanedioate ions, , form complexes with transition elements. The concentration of can be found by titration with acidified . 6. Write the half-equations for the oxidation of and the reduction of . 7. Construct the overall ionic equation for this reaction. 8. Describe the colour change observed at the end-point of this titration.

Redox Reactions: Copper(II) and Iodide (4 marks)

An excess of is added to an aqueous solution containing ions. All the copper is precipitated as white , and iodine is liberated. 9. Write the ionic equation for this reaction. 10. The liberated iodine is titrated with sodium thiosulfate, . Write the equation for this titration reaction.

Predicting Redox Feasibility using Data (3 marks)

A green precipitate of turns brown on standing in air. Using standard electrode potential data from the Data Booklet, explain why this occurs and construct an equation for the reaction.

Quantitative Redox Calculations (4 marks)

A sample containing iron(II) is dissolved in water and made up to . A sample of this solution requires of acidified to reach the end-point. Calculate the mass, in mg, of iron in the original sample. Show your working.

28.3 Colour of Complexes

Degenerate and Non-Degenerate Orbitals (2 marks)

The 3d orbitals in an isolated ion are degenerate.

1. Define the term degenerate.
2. Define the term non-degenerate in the context of transition metal complexes.

D-orbital Splitting Diagrams (2 marks)

Complete the energy level diagram to show the splitting of the 3d orbitals when an isolated transition metal ion forms:

1. An octahedral complex.
2. A tetrahedral complex.

Origin of Colour in Transition Metal Complexes (4 marks)

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

Effect of Ligand Exchange on Colour (3 marks)

A solution of is pale blue, while a solution of is deep blue/purple. Explain, in terms of d-orbitals and energy gaps (), why the solutions of these two complex ions are different colours.

Lack of Colour in Certain Ions (2 marks)

Solutions containing the complex or ions are colourless. Explain why these complexes do not exhibit colour.

28.4 Stereoisomerism in Transition Element Complexes

Types of Stereoisomerism (2 marks)

State the two types of stereoisomerism shown by transition element complexes.

Geometrical Isomerism in Square Planar Complexes (2 marks)

The complex displays geometrical isomerism. Draw the three-dimensional structures of the cis and trans isomers. State the shape and the bond angles.

Geometrical Isomerism in Octahedral Complexes (2 marks)

The complex exists as two stereoisomers. Draw the three-dimensional structures of both isomers.

Polarity of Isomers (2 marks)

Deduce which of the stereoisomers of or is polar and which is non-polar. Explain your answer in terms of dipole moments.

Optical Isomerism with Bidentate Ligands (3 marks)

The complex (where en is 1,2-diaminoethane) exhibits stereoisomerism. Draw three-dimensional diagrams to show the two stereoisomers of this complex, and state the type of stereoisomerism shown.

Combined Geometrical and Optical Isomerism (3 marks)

The complex exists in three isomeric forms. Draw the three-dimensional structures of these three isomers, identifying which two are optical isomers of each other.

28.5 Stability Constants,

Definition of Stability Constant (2 marks)

Define the term stability constant, , of a complex.

Writing Expressions (2 marks)

When is added to , the complex is formed. Write an expression for the stability constant, , for this equilibrium and deduce its units.

Interpreting Values (2 marks)

Table 1 shows the stability constants for various silver(I) complexes: () () Use this information to identify the most stable silver(I) complex and explain your reasoning.

Ligand Exchange and (2 marks)

An aqueous solution containing () is added to a solution containing equal concentrations of ions. The complex has a of . Predict what reaction, if any, will occur. Explain your answer with reference to the values.

Calculating Equilibrium Concentrations using (3 marks)

In a particular solution at equilibrium, the concentration of is and the concentration of is . Given that , calculate the concentration of the complex ion in this solution. Show your working.