Transition metals

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

This question is about complexes of the transition metal chromium.

State the meaning of the term transition metal complex.

Cr(PF₃)₆ is a complex of chromium that contains molecules of PF₃

The electron pair repulsion theory can be used to predict the shape of a PF₃ molecule.

Draw the shape of a PF₃ molecule. Include any lone pairs of electrons that influence the shape.

Name the shape.

Shape

Suggest why the oxidation state of chromium is zero in Cr(PF₃)₆

The compound [Cr(NH₃)₄Cl₂]Cl contains ammonia molecules.

Deduce the oxidation state of chromium in [Cr(NH₃)₄Cl₂]Cl

Name the type of bond between N and H in ammonia.

The compound [Cr(NH₃)₄Cl₂]Cl contains a complex ion that shows isomerism.

Draw the two isomers of the complex ion.

State the type of isomerism shown.

Isomer 1
Isomer 2

Type of isomerism

Complete the equation to show the formation of one complex that contains chromium in its +3 oxidation state.

Which shows the electron configuration of an atom of a transition metal?

Which will not act as a ligand in the formation of a complex ion?

Which shows the correct oxidation state and co-ordination number of cobalt in