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

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 K_stab of [Cu(NH₃)₄]²⁺. 

K_stab = 

[1]

 ii) State the colour of the solution of [Cu(NH₃)₄]²⁺. 

[1]

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.

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

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

Table 1.1

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

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.

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 ..............................................................................

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

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

Suggest the type of stereoisomers.

Compound A, C₄H₁₃N₃, is a tridentate ligand. 

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]

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]

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.

[2]

iv) State the change in coordination number. 

[1]

[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]

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

Suggest why the ammonium ion cannot act as a ligand.

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.

The structures of the ligands ethane-1,2-diamine and EDTA^4– are shown in Fig. 1.1.

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.

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.

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.

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

Fig. 2.1 shows some reactions of solution A.

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

Using complex ions formed by Cu²⁺ with ligands selected from H₂O, NH₃, Cl^–,  and EDTA^4–, 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]

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

Fig. 3.1

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

Explain why it is not possible to identify complex B.

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]

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]

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.

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.

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

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

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

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.

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

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