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) State the expression for the K_stab of [Cu(NH₃)₄]²⁺.

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

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The solution of [Cu(NH₃)₄]²⁺ is heated gently so that NH₃ is released. A precipitate of Cu(OH)₂ forms and is collected.

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

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

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

Construct 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.

Complete Table 1.2 to show the colour and state of the product, the ionic equation, and the type of reaction for each case.

Table 1.2

The [Fe(NH₃)₂(CN)₄]^– complex shows stereoisomerism.

Complete the three-dimensional diagrams to show the two isomers of [Fe(NH₃)₂(CN)₄]^–.

State the type of stereoisomerism shown.

Compound A, C₄H₁₃N₃, is a tridentate ligand.

i) Explain why one molecule of A can form three coordinate bonds.

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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.

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This question is about the transition metal copper.

i) State the full electronic configuration of a Cu atom and a Cu²⁺ ion.

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ii) State four characteristic features of the chemistry of copper and its compounds.

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

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

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ii) Construct an equation to represent the ligand substitution reaction.

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iii) Draw a diagram to show the structure of the complex ion formed.

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iv) State the geometry of the complex ion formed.

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v) State the change in coordination number.

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

i) Deduce the oxidation state of cobalt in this complex ion. Explain your answer.

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ii) State the geometry of this complex ion.

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

Explain 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

Compare the complex ions formed by cobalt(III) ions with each ligand. In your answer, state one similarity and three differences. 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. Explain your reasoning.

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.

Construct 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^–, C₂O₄^2– and EDTA^4–, construct 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.

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ii) A ligand substitution reaction with both a change in the coordination number and the charge on the complex ion.

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iii) A ligand substitution reaction with no change in the coordination number but a change in the charge on the complex ion.

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iv) A ligand substitution reaction with the greatest increase in entropy.

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

Fig. 3.1

Construct 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, construct the equation including state symbols to form compound C and other products.

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ii) State the type of reaction that occurs when compound C is converted into copper(II) oxide.

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

i) State the electronic configuration of a Cu⁺ ion.

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ii) Deduce the role of copper metal in the formation of [CuCl₄]^3– from the complex D.

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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.

Calculate the mass, in mg, of iron(II) gluconate in one tablet. Show your working and 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 working.

Construct 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 phenolphthalein as the indicator.

15.00 cm³ of the same H₂C₂O₄ (aq) required 12.35 cm³ of potassium manganate(VII), KMnO₄, solution for complete oxidation to carbon dioxide and water, in the presence of dilute sulfuric acid.

Calculate the concentration of the H₂C₂O₄ (aq) solution.

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

Calculate the concentration of the potassium manganate(VII), KMnO₄, solution.