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A LevelChemistryCIEExam Questions28. Chemistry of Transition Elements28.2 General Characteristic Chemical Properties of the First Set of Transition Elements, Titanium to Copper

General Characteristic Chemical Properties of the First Set of Transition Elements, Titanium to Copper (CIE A Level Chemistry)

Exam Questions

2 hours12 questions
Easy
Medium
Hard
1a2 marks

This question is about transition metal complexes. 

Define the terms ligand and complex.

 

Ligand = ............................................................ 

Complex = ..........................................................

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1b1 mark

Transition metals can form complexes with different ligands.

 

Identify one species from the following list that does not act as a ligand. Explain your answer.

 
CO         H2O         SCN-          H2 

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1c2 marks

A complex contains one Co2+ ion, four ammonia molecules and two chloride ions.

 
i)
State the formula of this complex.
 
[1]
 
ii)
Name the shape of this complex. 
 
[1]

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1d2 marks

The H2O ligands in [Fe(H2O)6]3+ can be exchanged for other ligands. 

 

Predict the shape of the complex ions formed after the following substitutions.

 

i)
All the H2O ligands are exchanged for OH– ligands.
 
[1]
 
ii)
The six H2O ligands are exchanged for four Cl– ligands.
 
[1]

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1e2 marks

Cisplatin can be used to treat some types of cancer.

 

It is a square planar transition metal complex with a central platinum(II) ion, two chloride ligands and two ammonia ligands.

 

Complete the three-dimensional diagram in Fig. 1.1 to show the shape of cisplatin. Label and state the value of one bond angle.

 
 
 
 
Pt
 
 
 
Fig. 1.1 

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2a2 marks

This question is about ligand exchange in copper(II) complexes.

Complete Table 2.1 to show whether the coordination number and shape of the complex changes in the given situations.

 
Table 2.1 
 
  Ligand exchange of similarly sized ligands Ligand exchange of differently sized ligands
Coordination number    
Shape    
 

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2b1 mark

When copper(II) sulfate dissolves in water, the conventional equation for this can be represented as

 
CuSO4 (s) + aq → Cu2+ (aq) + SO42– (aq) 
 

State the formula of the hexaaquacopper(II) complex represented by Cu2+ (aq).

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2c2 marks

Complete the three-dimensional diagram in Fig. 2.1 to show the hexaaquacopper(II) ion complex.

 
 
 
 
Cu
 
 
 
 
Fig. 2.1 

 

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2d2 marks

Hexaaquacopper(II) ions react with concentrated hydrochloric acid to form complex A.

 

Complete Table 2.2 with the colour and geometry of the hexaaquacopper(II) complex and the colour, geometry and formula of complex A.

 
Table 2.2 
 
  Hexaaquacopper(II) complex A
colour of complex    
geometry of complex    
formula of complex    
 

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2e3 marks

In the presence of concentrated ammonia, hexaaquacopper(II) initially reacts to form Cu(OH)2(H2O)4.

 
i)
Give the colour and state of Cu(OH)2(H2O)4.
 
colour ..................................................
 
state ..................................................
 
[1]
 
ii)
In the presence of excess concentrated ammonia, the Cu(OH)2(H2O)4 further reacts to form [Cu(NH3)4(H2O)2]2+.
 
Give the colour and state of [Cu(NH3)4(H2O)2]2+.
 
colour ..................................................
 
state ..................................................
 
[1]
 
iii)
The [Cu(NH3)4(H2O)2]2+ formed is a mixture of two geometrically isomeric octahedral complexes.
 
Fig. 1.2 shows the three-dimensional diagram of the trans isomer. Complete Fig. 1.2 to show the three-dimensional diagram of the cis isomer.
 
cuii-conc-ammonia-cis-trans-q
 
Fig. 1.2 
 
[1]

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3a2 marks

The feasibility of redox reactions can be determined using standard electrode potential, Eθ, values.

The following electrochemical cell is set up.

 
Pb4+ (aq) + 2Mn2+ (aq) → 2Mn3+ (aq) + Pb2+ (aq) 
 
Table 3.1
 
Electrode reaction Eθ / V
Mn2+ + 2e– ⇌ Mn – 1.18
Mn3+ + e– ⇌ Mn2+ + 1.49
Pb2+ + 2e– ⇌ Pb – 0.13 
Pb4+ + 2e– ⇌ Pb2+ + 1.69

 
Use Table 3.1 to determine the half-equations for reduction and oxidation. Your half-equations should be written in the conventional reduction format. 

Reduction half-equation ...................................................................... 

Oxidation half-equation ...................................................................... 

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3b
Sme Calculator1 mark

Use Table 3.1 and your answer to part (a) to calculate the standard cell potential, Eθcell, for the reaction.

 
Eθcell = ...................... V

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3c1 mark

Use your answer to part (b) to suggest whether the reaction is feasible. Explain your answer.

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4a2 marks

Potassium manganate(VII) can be used to titrate a sample containing an unknown percentage of iron(II).

i)
Complete the half-equation for the reduction of manganate ions, MnO4–, to manganese ions, Mn2+.
 
MnO4– (aq) + ........H+ (aq) + ........e– → Mn2+ (aq) + ........H2O (aq)
 
[1]
 
ii)
Explain whether this reaction is oxidation or reduction.
 
[1]

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4b2 marks
i)
Write the half-equation for the oxidation of Fe2+ to Fe3+. Your answer should include state symbols. 
 
[1]
 
ii)
Explain whether this reaction is oxidation or reduction.
 
[1]

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4c2 marks

Using your answers to parts (a) and (b), write the full equation for the reaction between Fe2+ ions and MnO4– ions.

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1a2 marks

A solution is made by dissolving CuSO4•5H2O in an excess of aqueous ammonia. This solution contains the copper complex [Cu(NH3)4]2+.

i)
Write an expression for the Kstab of [Cu(NH3)4]2+.
 
Kstab =
 
[1]
 
ii)
State the colour of the solution of [Cu(NH3)4]2+.
 
[1]

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1b1 mark

The solution of [Cu(NH3)4]2+ is heated gently in a fume cupboard so that NH3 is released. Some NH3 remains in solution and some forms NH3 gas. The colour of the solution changes; a precipitate of Cu(OH)2 forms and is collected.

A sample of Cu(OH)2 is added to concentrated hydrochloric acid. A reaction takes place forming a coloured copper complex, Y.

A sample of Cu(OH)2 is added to dilute sulfuric acid. A reaction takes place forming a coloured copper complex, Z.

[Cu(NH3)4]2+, Y and Z are different colours.

Suggest an equation for the reaction of [Cu(NH3)4]2+ to form Cu(OH)2 as the aqueous solution of [Cu(NH3)4]2+ is heated.

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1c2 marks

Suggest an equation for the reaction of Cu(OH)2 with concentrated hydrochloric acid, forming Y.

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1d2 marks

Complete Table 1.1 with the colour and geometry of complex Y and the colour, geometry and formula of complex Z.

Table 1.1

  Y Z
colour of complex    
geometry of complex    
formula of complex    
 

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1e5 marks

Explain why complexes Y and Z are coloured and why their colours are different.

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2a1 mark

This question is about transition metal complexes.

An aqueous solution of copper(II) contains the [Cu(H2O)6]2+ complex ion.

 

Define the term complex ion.

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2b6 marks

A sample of [Cu(H2O)6]2+ is reacted with aqueous sodium hydroxide and a separate sample of [Co(H2O)6]2+ with an excess of aqueous ammonia.

 

Give the following information about these reactions.

  • the reaction of [Cu(H2O)6]2+ with aqueous sodium hydroxide
     
    colour and state of the copper-containing species

    .......................................................................................................
     
    ionic equation ................................................................................
     
    type of reaction ..............................................................................

  • the reaction of [Co(H2O)6]2+ with an excess of aqueous ammonia
     
    colour and state of the cobalt-containing species

    .......................................................................................................
     
    ionic equation ................................................................................
     
    type of reaction ..............................................................................

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2c3 marks

The [Fe(NH3)2CN4]– complex shows stereoisomerism.

 

Complete the three-dimensional diagrams to show the two isomers of  [Fe(NH3)2CN4]–.

 
6-3-2c-m-fe-txn-isomers-b
 

Suggest the type of stereoisomers.

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2d2 marks

Compound A, C4H13N3, is a tridentate ligand. 

 
6-3-2d-m-tridentate-ligand-example
 
i)
Suggest why one molecule of A can form three dative bonds.
 
[1]
 
ii)
C4H13N3 reacts with aqueous chromium(III) ions, [Cr(H2O)6]3+, in a 2:1 ratio to form a new complex ion.
 
Construct an equation for this reaction.
 
[1]

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3a6 marks

This question is about the transition metal copper.

i)
Give the full electronic configuration of a Cu atom and a Cu2+

Cu: .................................................................

Cu2+: .............................................................
[2]
ii)
State four characteristic features of the chemistry of copper and its compounds.
 
characteristic 1 ....................................................................................
 
characteristic 2 ....................................................................................
 
characteristic 3 ....................................................................................
 
characteristic 4 ....................................................................................
[4]

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3b5 marks

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

i)
Explain what is meant by the term monodentate ligand.
[1]
ii)
Write an equation to represent the ligand substitution reaction.
[1]
iii)
Draw a diagram to show the structure of the complex ion formed and name the shape it takes.

screenshot-2024-03-18-110656

[2]

iv)
State the change in coordination number. 
[1]

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3c6 marks

[Co(NH3)4Cl2]+ is an example of a complex containing cobalt.

i)
Deduce the oxidation number of cobalt in this complex. Explain your answer
 
oxidation number: ..................................................
 
explanation: .......................................................................................................................................

[2]

ii)
State the shape of this complex.
 
shape: ..................................................

[1]

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1a1 mark

Complex ions have a central transition metal ion surrounded by ligands.

Suggest why the ammonium ion cannot act as a ligand.

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1b4 marks

Explain why the complex ions [Co(NH3)6]2+ and [Co(H2O)6]2+ both form coloured solutions but exhibit different colours to each other.

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1c4 marks

The structures of the ligands ethane-1,2-diamine and EDTA4– are shown in Fig. 1.1.

ethane-1-2-diamine edta4-
ethane-1,2-diamine EDTA4– 

 Fig. 1.1

State the similarities and differences between the complex ions formed by cobalt(III) ions with each ligand. Ignore any difference in colour.

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1d2 marks

Hydrated chromium(III) chloride, CrCl3.6H2O, dissolves in water to form a number of different complex ions containing both chloride and water ligands.

The general formula of these complex ions is [Cr(H2O)x(Cl)y](3–y)+

In an experiment, 0.10 mol of a complex reacted with excess silver nitrate solution to produce 0.20 mol of silver chloride.

Chloride ions which are ligands within the complex do not react with silver nitrate.

Deduce the formula of this chromium(III) complex ion. Justify your answer.

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2a1 mark

Cobalt(II) and copper(II) undergo similar reactions to each other.

Cobalt(II) nitrate and copper(II) nitrate both decompose in a similar manner to that of Group 2 nitrates.

Write an equation for the thermal decomposition of Co(NO3)2.

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2b4 marks

Co(NO3)2 is added to water to form solution A.

Fig. 2.1 shows some reactions of solution A.

6-2-2b-h-cobalt-nitrate-reaction-scheme

Fig 2.1

Complete Table 2.1 to show the state, formula and colour of each of the cobalt-containing species present in A, B and C.

Table 2.1

  State of cobalt-containing species formed Formula of cobalt-containing species formed Colour of cobalt-containing species formed
A      
B      
C      
D      

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2c8 marks

Using complex ions formed by Cu2+ with ligands selected from H2O, NH3, Cl–,  and EDTA4–, give an equation for each of the following.

i)
A ligand substitution reaction with no change in the coordination number or the charge on the complex ion.
 
[2]
 
ii)
A ligand substitution reaction with both a change in the coordination number and the charge on the complex ion.
 
[2]
 
iii)
A ligand substitution reaction with no change in the coordination number but a change in the charge on the complex ion.
 
[2]
 
iv)
A ligand substitution reaction where there is a large change in entropy.
 
[2]

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3a2 marks

Fig. 3.1 shows a reaction pathway involving various copper(II) species.

6-2-3a-h-copper-carbonate-reaction-scheme

Fig. 3.1

Write the equation for the formation of complex D from complex A.

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3b2 marks

Explain why it is not possible to identify complex B.

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3c4 marks
i)
Using the information in Fig. 3.1, write the equation including state symbols to form compound C and other products.
 
[3]
 
ii)
Identify the type of reaction that occurs when compound C is converted into copper(II) oxide.
 
[1]

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3d2 marks

The oxidation number of copper in [CuCl4]3– is +1.

i)
Give the electronic configuration of a Cu+ ion.
 
[1]
 
ii)
Deduce the role of copper metal in the formation of [CuCl4]3– from the complex D.
 
[1]

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4a
Sme Calculator4 marks

Iron(II) gluconate, C12H22FeO14, is the active ingredient in some brands of iron supplements.

A student carries out an experiment to determine the mass of iron(II) gluconate in one tablet of an iron supplement, using the method below.

  1. The student crushes two tablets and dissolves the powdered tablets in dilute sulfuric acid
  2. The student makes up the solution from step 1 to 250.0 cm3 in a volumetric flask.
  3. The student then titrated 25.0 cm3 portions of the solution obtained in step 2 with 0.00200 mol dm−3 potassium manganate(VII).

The student obtains a mean titre of 13.50 cm3.

In this titration, 1 mole of manganate(VII) ions reacts with 5 moles of iron(II) ions.

Determine the mass, in mg, of iron(II) gluconate in one tablet. Give your answer to 3 significant figures.

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4b
Sme Calculator2 marks

The typical concentration of a potassium manganate(VII) solution used in redox titrations is 0.0200 mol dm-3.

Use the information in part (a) to explain, quantitatively, why the student replaced this with a 0.00200 mol dm-3 potassium manganate(VII) solution for this titration.

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4c
Sme Calculator1 mark

Some iron supplements contain iron(II) sulfate or iron(II) fumarate.

Table 4.1 shows the information taken from the labels of two iron supplements, A and B.

Table 4.1

Iron
supplement

Iron
compound

Mass of iron compound
in one tablet / mg

A

Iron(II) sulfate, FeSO4

180

B

Iron(III) fumarate, C4H2FeO4

210

 

State which iron supplement, A or B, would provide the greater mass of iron per tablet. Show your workings.

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5a1 mark

Write an equation for the reaction between ethanedioic acid, H2C2O4, and sodium hydroxide, NaOH.

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5b3 marks

15.00 cm3 of H2C2O4 (aq) requires 10.30 cm3 of a 0.25 mol dm-3 solution of NaOH for complete neutralisation using a phenolphthalein indicator for the first permanent colour change. 

15.00 cm3 of the same H2C2O4 (aq) required 12.35 cm3 of potassium permanganate, KMnO4, solution for complete oxidation to carbon dioxide and water in the presence of dilute sulfuric acid to further acidify the H2C2O4 (aq) for the first permanent
colour change. 

Calculate the moles of H2C2O4 (aq) therefore the concentration of the solution.

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5c3 marks

Write the full redox equation, including state symbols, for this redox titration.

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5d2 marks

Calculate the concentration of the potassium permanganate, KMnO4, solution.

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