A LevelChemistryCambridge (CIE)Exam Questions28. Chemistry of Transition ElementsStereoisomerism in Transition Element Complexes

Stereoisomerism in Transition Element Complexes (Cambridge (CIE) A Level Chemistry): Exam Questions

Exam code: 9701

41 mins4 questions
Medium
Hard
1a
2 marks

Cobalt is a transition element with atomic number 27.

Complete the electronic configurations of a Co atom and a Co2+ ion.

Co atom   1s2 2s2 2p6  ..................................

Co2+ ion   1s2 2s2 2p6  ..................................

How did you do?

1b
2 marks

When concentrated hydrochloric acid is added to a solution containing [Co(H2O)6]2+, a ligand exchange reaction occurs.

Draw a three-dimensional diagram to show the shape of the complex ion formed. Include the overall charge.

overall charge ......................................

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1c
3 marks

Co2+ ions exist as [Co(H2O)6]2+ complex ions in aqueous solution.

Complete the three-dimensional diagram to show the shape of this complex. State the geometry. On your diagram, state the bond angle.

Blank three-dimensional octahedral diagram of [Co(H2O)6]2+ with cobalt at the centre and positions for six water ligands to be added

geometry ..................................................

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1d
4 marks

When aqueous ammonia, NH3 (aq), is added to [Co(H2O)6]2+ (aq), dropwise at first and then in excess, two distinct chemical reactions occur. For each reaction, state the expected observations and construct an equation.

i) Addition of a few drops of NH3 (aq)

observation .............................................................................

equation ..................................................................................

[2]

ii) Addition of an excess of NH3 (aq)

observation .............................................................................

equation ..................................................................................

[2]

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1e
5 marks

EDTA4- is a hexadentate ligand. When a solution of EDTA4- is added to a solution containing [Co(H2O)6]2+, a new complex is formed. The formula of this complex is [CoEDTA]2-.

i) Explain what is meant by the term hexadentate ligand.

[2]

ii) State the type of reaction occurring here.

[1]

iii) Write an expression for the stability constant, Kstab, of [CoEDTA]2- in this reaction.

[1]

iv) The numerical value of the Kstab of [CoEDTA]2- is 7.7 x 104 mol-1 dm3 at 298 K.

Deduce what this value indicates about the stability of [CoEDTA]2- compared to [Co(H2O)6]2+.

[1]

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2a
4 marks

The chloride ion is a monodentate ligand. When concentrated hydrochloric acid is added to [Co(H2O)6]2+(aq) ions the water ligands are replaced.

i) Construct an equation for the reaction of [Co(H2O)6]2+(aq) with concentrated hydrochloric acid. Include state symbols.

[2]

ii) Draw the three-dimensional diagram to show the complex formed in the reaction between [Co(H2O)6]2+(aq) and HCl.

[2]

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2b
4 marks

[Co(NH3)4Cl2]+ is an example of an octahedral complex which exhibits cis-trans isomerism.

i) Deduce the oxidation state of cobalt in [Co(NH3)4Cl2]+.

[1]

ii) Draw three-dimensional diagrams of the two [Co(NH3)4Cl2]+ isomers. Label each isomer as cis or trans.

[3]

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2c
4 marks

Explain the origin of colour in a transition element complex such as [Co(NH3)4Cl2]+.

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3a
1 mark

Bidentate ligands form two coordinate bonds to a central metal atom or ion in a complex.

State what is meant by a bidentate ligand.

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3b
3 marks

The product of the reaction between [Cu(H2O)6]2+ and 1,2-diaminoethane exists as a pair of optical isomers.

Draw three-dimensional diagrams to show the two optical isomers.

How did you do?

3c
2 marks

1,2-diaminoethane is an example of a compound which is a bidentate ligand. Full ligand substitution occurs when 1,2-diaminoethane is added to [Cu(H2O)6]2+.

Construct an equation for the reaction of [Cu(H2O)6]2+ with 1,2-diaminoethane. Include state symbols.

How did you do?

1a
2 marks

Several platinum complexes, including oxoplatin, iproplatin, ormaplatin and satraplatin, are used as anti-cancer drugs. The central platinum ions in the four complexes shown in Fig. 1.1 all have the same geometry and oxidation state.

Structural diagrams of four platinum anti-cancer drug complexes: oxoplatin, iproplatin, ormaplatin and satraplatin

Fig. 1.1

State the oxidation state of the platinum ion and the geometry of these complexes.

oxidation state of the platinum ion ..................................................

geometry of the complexes ..................................................

How did you do?

1b
4 marks

One isomer of the [Pt(NH3)2Cl2(OH)2] complex oxoplatin is shown in (a) Fig. 1.1.

Draw three-dimensional diagrams to show the other stereoisomers of oxoplatin. State which of these stereoisomers are chiral.

Blank three-dimensional octahedral templates for drawing oxoplatin stereoisomers

How did you do?

1c
1 mark

Cisplatin can be produced by the reduction of the complex cis, trans, cis-[PtCl2(OCOCH3)2(NH3)2].

Draw a three-dimensional diagram to show the structure of cis, trans, cis-[PtCl2(OCOCH3)2(NH3)2].

How did you do?