Ligand substitution reactions

This question is about the chemistry of copper.

Deduce the number of unpaired electrons in a Cu²⁺ ion.

Describe how water acts as a ligand in the formation of [Cu(H₂O)₆]²⁺

A solution of sodium carbonate is added to a blue solution containing

State what is observed.

Give an equation for the reaction.

Equation

When a solution containing [Cu(H₂O)₆]²⁺ ions reacts with an excess of concentrated hydrochloric acid, a ligand exchange reaction occurs.

Blue Yellow

The shape and the colour of the [CuCl₄]^2– ion are different from the shape and the

Explain

• the shape of each complex ion and why these shapes are different

• how colour arises in complex ions

• why the [CuCl₄]^2– ion has a yellow colour, different from the blue colour of the

An excess of water, followed by an excess of concentrated aqueous ammonia, is added to a solution containing [CuCl₄]^2– ions.

State what is observed.

Give an equation for the overall change that occurs.

Equation

A solution contains M₂[Cu(C₂O₄)₂(H₂O)₂] where M is a metal.

A student does a titration to determine the identity of M.

• 2.52 g of solid M₂[Cu(C₂O₄)₂(H₂O)₂] are dissolved in dilute sulfuric acid.

• This solution is transferred to a volumetric flask and made up to 250 cm³ with dilute sulfuric acid.

• A 25.0 cm³ portion is pipetted into a conical flask.

• The mixture in the conical flask is heated to 60 °C and then titrated with 0.0200 mol dm^–3 KMnO₄ solution.

• Several titrations are done and the student’s results are shown in Table 3.

In this titration, only the C₂O₄^2– ions react with the MnO₄^– ions. 2 mol of MnO₄^– ions react with 5 mol of C₂O₄^2– ions.

Give an equation for the reaction between C₂O₄^2– ions and MnO₄^– ions in acidic solution.

Calculate the mean titre from the student’s results.

Calculate the M_r of M₂[Cu(C₂O₄)₂(H₂O)₂]

Identify M.

Draw the structure of two stereoisomers of the complex ion in M₂[Cu(C₂O₄)₂(H₂O)₂] and include the charge on each structure.

Structure 1
Structure 2

Which reaction produces an octahedral complex ion ?

This question is about aqueous ions of the metal iron.

When an aqueous [Fe(H₂O)₆]³⁺ ion reacts with ethanedioate ions, an iron(III) complex ion X is formed.

The only ligands in X are ethanedioate ions.

Draw the structure of X.

Include the charge.

The formation of X is an example of the chelate effect.

Explain the meaning of the chelate effect.

Outline how Fe²⁺ ions catalyse the reaction between S₂O₈^2– ions and I^– ions in aqueous solution.

In your answer you should include

• a sketch graph to show how the concentration of S₂O₈^2– ions changes over time

• an explanation of how Fe²⁺ ions catalyse the reaction, including equations

• an overall equation for the reaction.

A student adds dilute ammonia solution to a solution containing [Fe(H₂O)₆]²⁺ ions.

Give the formula of the precipitate that forms.

The student adds sodium carbonate solution to a solution containing

State one observation the student would make.

Give an equation for the reaction.

Equation

A solution containing [Fe(H₂O)₆]²⁺ ions changes to a yellow-brown colour after several hours in contact with air.

The student adds sodium carbonate to the yellow-brown solution.

Give an equation for the reaction with sodium carbonate.

This question is about complexes containing the aluminium ion.

Give the electron configuration of the Al³⁺ ion.

When anhydrous aluminium sulfate, Al₂(SO₄)₃, is added to water a solution forms that contains the complex aluminium ion, [Al(H₂O)₆]³⁺

Give the equation for the reaction.

Explain why the solution containing [Al(H₂O)₆]³⁺ is acidic.

State why the concentration of aluminium sulfate solution can not be determined by

An excess of aqueous ammonia is added to a solution containing [Al(H₂O)₆]³⁺

Give an ionic equation for the reaction and state one observation.

Equation

An excess of dilute sulfuric acid is added to the products of the reaction in Question 07.5

Identify the aluminium species produced.

Figure 3 shows the structure of the EDTA^4– ion.

Atoms of two different elements in EDTA^4– can form co-ordinate bonds with an aluminium ion.

On Figure 3, draw circles around the atoms of two different elements that would link to an aluminium ion by a co-ordinate bond.

Hydrated aluminium sulfate, Al₂(SO₄)₃.xH₂O, is soluble in water.

The relative formula mass and value of x can be found from a titration experiment.

Aqueous [Al(H₂O)₆]³⁺ ions react to form a stable complex when treated with an excess

The excess of EDTA^4– ions is determined by titration with ZnSO₄ solution.

• Dissolve 1.036 g of Al₂(SO₄)₃.xH₂O in distilled water and make up to 250 cm³

• Add 25.0 cm³ of this solution to 50.0 cm³ of a solution containing EDTA^4– ions of concentration 0.0100 mol dm^–3

• Determine the excess of EDTA^4– ions by titrating with ZnSO₄ solution in the presence of an indicator.

The excess of EDTA^4– ions requires 18.00 cm³ of 0.0105 mol dm^–3 ZnSO₄ solution to

The equations for the reactions are

Use the information given to calculate the M_r of Al₂(SO₄)₃.xH₂O

Give your answer as an integer.

There are no questions on this page

Copper(II) complexes are coloured. The colour is caused by the d electrons of copper moving from their ground state to an excited state.

Explain why aqueous solutions containing [CuCl₄]^2– ions are yellow.

When a d electron moves from the ground state to the excited state in a copper complex, the energy change is 3.98 x 10^–19 J

Calculate the frequency, in s^–1, of the light absorbed.

State three ways in which a transition metal complex can be changed to alter its colour.

Consider the following reaction scheme in which P, Q and R are different complex ions of copper.

Name the shape of the [CuCl₄]^2– ion.

Give an ionic equation for the conversion of [CuCl₄]^2– to complex ion P.

State the colour of the solution containing the complex ion Q.

Give an ionic equation for the conversion of [CuCl₄]^2– to Q.

Equation

Identify complex ion R.

Cobalt(II) chloride solution changes colour when an excess of concentrated hydrochloric acid is added.

What type of reaction takes place?

This question is about ethanedioic acid (HOOCCOOH) and the ethanedioate ion (⁻OOCCOO⁻).

Ethanedioic acid reacts with propane-1,3-diol (HOCH₂CH₂CH₂OH) to form a polyester.

Draw the repeating unit of this polyester.

Explain why polyesters are biodegradable but polyalkenes are not biodegradable.

Sodium ethanedioate is used to find the concentration of solutions of potassium manganate(VII) by titration. The equation for this reaction is

A standard solution is made by dissolving 162 mg of Na₂C₂O₄ (M_r = 134.0) in water and making up to 250 cm³ in a volumetric flask.

25.0 cm³ of this solution and an excess of sulfuric acid are added to a conical flask. The mixture is warmed and titrated with potassium manganate(VII) solution. The titration is repeated until concordant results are obtained.

Calculate the concentration, in mol dm^–3, of the potassium manganate(VII) solution.

Figure 1 shows the 25.0 cm³ pipette used to measure the sodium ethanedioate solution.

On Figure 1, draw the meniscus of the solution when the pipette is ready to transfer 25.0 cm³ of the sodium ethanedioate solution.

Potassium manganate(VII) is oxidising and harmful. Sodium ethanedioate is toxic.

Suggest safety precautions, other than eye protection, that should be taken when:

• filling the burette with potassium manganate(VII) solution

• dissolving the solid sodium ethanedioate in water.

Filling the burette

Dissolving the solid

State the colour change seen at the end point of each titration.

Figure 2 shows the burette containing potassium manganate(VII) solution.

Give two practical steps needed before recording the initial burette reading.

When Na₂C₂O₄(aq) is added to a solution containing [Fe(H₂O)₆]³⁺ ions, a reaction occurs in which all six water ligands are replaced by ethanedioate ions.

Explain why the replacement of the water ligands by ethanedioate ions is favourable. In your answer refer to:

• the enthalpy and entropy changes for the reaction

• how the enthalpy and entropy changes influence the free-energy change for the reaction.

Some reactions of the [Al(H₂O)₆]³⁺(aq) ion are shown.

Give the formula of the white precipitate B.

State one other observation when Na₂CO₃(aq) is added to a solution containing

Give an equation for this reaction.

Equation

Give the formula of the complex ion C.

State one condition needed for the formation of C from [Al(H₂O)₆]³⁺(aq) and NaOH(aq).

Give an equation for this reaction.

Equation

Deduce the formula of the complex ion A.

Explain, with the use of an equation, why a solution containing [Al(H₂O)₆]³⁺ has a pH ˂7

Equation

Figure 3 shows some reactions of aqueous iron ions.

Give the formula of Precipitate J and state its colour. Give an equation for Reaction 1.

Equation

Give the formula of L and an equation for Reaction 2.

Equation

Suggest a reagent for Reaction 3.

Give the formula of Precipitate M and state its colour.

Transition metal complexes have different shapes and many show isomerism.

Describe the different shapes of complexes and show how they lead to different types of isomerism. Use examples of complexes of cobalt(II) and platinum(II).

You should draw the structures of the examples chosen.

What is observed when concentrated hydrochloric acid is added to an aqueous solution of CuSO₄ until no further change occurs?

Which statement is correct about this reaction?