Ligand substitution reactions

This question is about transition elements.

Suggest the formulae of A, B and C.

Complex ion A:........

Solid B:........

Complex ion C:........

Cobalt (III) forms an octahedral complex ion D, which contains both ammonia and chloride ligands.

Complex ion D has a molar mass of 197.9 g mol^–1.

Determine the formula and charge of complex ion D.

Red blood cells contain haemoglobin which transports oxygen around the body.

For efficient transportation of oxygen, healthy human blood must be maintained at a pH value between 7.35 and 7.45.

Human blood acts as a buffer due to the presence of carbonic acid, H₂CO₃, and hydrogencarbonate, HCO₃^–, ions as shown below.

• Explain, using ligand substitution, how haemoglobin transports oxygen around the body.

• Determine whether a sample of blood with a [HCO₃^–]: [H₂CO₃] ratio of 8.5:1 is healthy.

This question is about the d-block elements in Period 4 of the periodic table (Sc to Zn).

* Explain, with examples from Period 4, what is meant by the terms d-block element and transition element.

Explain why some d-block elements are not transition elements.

Use electron configurations to support your explanations.

Describe precipitation reactions using either copper or chromium ions as examples.

Include equations.

Describe ligand substitution reactions using either copper or chromium ions as examples.

Include equations.

The ethanedioate ion, C₂O₄^2–, is a bidentate ligand.

A complex ion of cobalt(III) contains two ethanedioate ligands and two water ligands.

Determine the charge of this complex ion and the coordination number of cobalt in the complex ion.

Charge of complex ion........

Coordination number of cobalt........

An acidified solution containing Cr₂O₇^2– ions reacts with vanadium(III) ions in a redox reaction to form a solution containing Cr³⁺ ions and VO₂⁺ ions.

Construct the overall equation for this reaction.

Tutton’s salts are ‘double salts’ with the formula X₂Y(ZO₄)₂ • 6H₂O.

A Tutton’s salt contains two cations: X⁺ and Y²⁺.

• X + can be an ion of the Group 1 elements K, Rb, Cs or Fr, or an ammonium ion.

• Y²⁺ can be a 2+ ion of magnesium or an ion of most of the transition elements in Period 4.

• Z can be S or Cr.

(NH₄)₂Cu(SO₄)₂ • 6H₂O is an example of a Tutton’s salt.

Predict the formula of a Tutton’s salt containing different ions from (NH₄)₂Cu(SO₄)₂ • 6H₂O.

A student prepares a sample of the Tutton’s salt, (NH₄)₂Cu(SO₄)₂ • 6H₂O using the method shown below.

Step 1 Dissolve 0.025 mol of ammonium sulfate and 0.025 mol of hydrated copper(II) sulfate, CuSO₄ • 5H₂O, in water and make up to 50 cm³.

Step 2 Boil the resulting mixture for 2 minutes and allow to cool.

Step 3 Allow the solvent to evaporate slowly. Pale blue crystals of the Tutton’s salt form.

What masses are needed of ammonium sulfate and CuSO₄ • 5H₂O?

mass of ammonium sulfate........ g

mass of CuSO₄ • 5H₂O........ g

In Step 3, why does the student allow the solvent to evaporate and not boil off all the solvent in Step 2 ?

The student dissolves their Tutton’s salt in water. A pale blue solution forms.

The student carries out two tests on this aqueous solution.

The student adds an excess of aqueous ammonia to their aqueous solution of Tutton’s salt. A deep blue solution forms.

The complex ion responsible for the deep blue solution has a molar mass of 167.5 g mol^–1.

Suggest the formula of this complex ion.

The student adds NaOH(aq) to the aqueous solution of Tutton’s salt and warms the mixture.

A precipitate and a gas are formed.

Write the formulae of the precipitate and gas and suggest a test that could confirm the identity of the gas.

Formula of precipitate........

Formula of gas........

Test to confirm the identity of the gas........

How could the student carry out a test-tube test to confirm the anion in the Tutton’s salt?

This question is about reactions of transition metal compounds.

Explain why ethane-1,2-diamine can act as a bidentate ligand.

The iron(III) ion, Fe³⁺, forms a complex ion A with two ethane-1,2-diamine ligands and two chloride ligands.

Complex ion A has cis and trans stereoisomers. One of these stereoisomers exists as optical isomers.

Determine the empirical formula, with charge, of complex ion A and draw the 3-D structures of the three stereoisomers.

Empirical formula with charge........

Structures

Aqueous sodium hydroxide is added to an aqueous solution of iron(II) sulfate. A pale green precipitate forms which turns brown when left to stand in air.

Write an ionic equation for the formation of the pale green precipitate.

* This question is about copper and copper compounds.

Experiment 1 Hydrochloric acid, HCl (aq), is added to an aqueous solution containing [Cu(H₂O)₆]²⁺ complex ions. A yellow-green solution forms containing complex ion B.

Experiment 2 A piece of copper metal is heated with concentrated sulfuric acid. A reaction takes place forming a pale blue solution C and 45 cm³ of a gas D, measured at RTP. The mass of gas D is 0.12 g.

Experiment 3 An excess of copper(II) oxide is heated with dilute nitric acid. The resulting mixture is filtered. The filtrate is a blue solution E. Aqueous potassium iodide, K I (aq), is added to the blue solution E. A white precipitate F and a brown solution G form.

Determine the formulae of B – G. Construct equations for the reactions taking place, include any changes in oxidation number,

and show your working where appropriate.

Healthy human blood needs to be maintained at a pH of 7.40 for the body to function normally.

Red blood cells contain haemoglobin.

Explain using ligand substitutions:

• how haemoglobin transports oxygen around the body

• why carbon monoxide is toxic.

This question is about reactions of ions and compounds of transition elements.

A student carries out two experiments on a solution containing [Cr(H₂O)₆]³⁺(aq).

Experiment 1 The student adds an excess of aqueous ammonia to a solution containing [Cr(H₂O)₆]³⁺ until a purple solution is formed.

Experiment 2 The student carries out the following reaction sequence.

Step 1 NaOH(aq) is added slowly to a solution containing [Cr(H₂O)₆]³⁺(aq) in a boiling tube. A grey–green precipitate forms.

Step 2 An excess of NaOH(aq) is added to the boiling tube. The precipitate dissolves and a green solution forms containing a 6 coordinate complex ion.

Step 3 H₂O₂ is added to the mixture and the boiling tube is heated. A yellow solution forms.

Step 4 The solution in the boiling tube is acidified. The solution now contains Cr₂O₇²⁻(aq).

What is the formula of the complex ion in the purple solution that forms in Experiment 1

Suggest an equation for the reaction in Experiment 2, Step 1. Include state symbols.

Draw a 3-D diagram for the shape of the complex ion that forms in Experiment 2, Step 2 Include the charge of the ion.

What is the formula of the ion that causes the yellow colour in Experiment 2, Step 3

State the colour of the solution that forms in Experiment 2, Step 4.

Vanadium ions have four common oxidation states. Table 18.1 shows the colours of the ions in aqueous solution.

Complete the electron configuration of a V³⁺ ion.

The student adds excess iron to a solution containing VO²⁺(aq) ions, and observes that the colour of the solution changes from blue to green and then to violet.

Use the relevant standard electrode potentials shown in Table 18.2 to explain these observations.

Construct an equation for the first colour change from blue to green.

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.

Stage 1 The student crushes two tablets and dissolves the powdered tablets in dilute sulfuric acid.

Stage 2 The student makes up the solution from Stage 1 to 250.0 cm³ in a volumetric flask.

Stage 3 The student then titrates 25.0 cm³ portions of the solution obtained in Stage 2 with 0.00200 mol dm⁻³ potassium manganate(VII).

The student obtains a mean titre of 13.50 cm³.

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

Explain why the student used 0.00200 mol dm⁻³ potassium manganate(VII) solution for this titration, rather than the more usual concentration of 0.0200 mol dm⁻³ used in manganate(VII) titrations.

Use the student’s results to determine the mass, in mg, of iron(II) gluconate in one tablet.

Give your answer to 3 significant figures.

This question is about some reactions of d block elements and their ions.

Table 21.1 shows standard electrode potentials which will be needed within this question.

Complete the electron configuration of

a Ni atom: 1s²........

a Ni²⁺ ion: 1s²........

A standard cell is set up in the laboratory with the cell reaction shown below.

Draw a labelled diagram to show how this cell could be set up to measure its standard cell potential.

Include details of apparatus, solutions and the standard conditions required.

Standard conditions........

Predict the standard cell potential of this cell.

Use the information in Table 21.1 to help you answer both parts of this question.

Write the overall equation for the oxidation of Fe²⁺ by acidified H₂O₂.

Zinc reacts with acidified Cr₂O₇^2– ions to form Cr²⁺ ions in two stages.

Explain why this happens in terms of electrode potentials and equilibria.

Include overall equations for the reactions which occur.

* Three different reactions of copper compounds are described below.

Reaction 1: Aqueous copper(II) sulfate reacts with excess aqueous ammonia in a ligand substitution reaction. A deep-blue solution is formed, containing an octahedral complex ion, C, which is a trans isomer.

Reaction 2: Copper(I) oxide reacts with hot dilute sulfuric acid in a disproportionation reaction. A blue solution, D, and a brown solid, E are formed.

Reaction 3: Copper(II) oxide reacts with warm dilute nitric acid in a neutralisation reaction, to form a blue solution. Unreacted copper(II) oxide is filtered off, and the solution is left overnight in an evaporating basin. A hydrated salt, F, crystallises, with the percentage composition by mass: Cu, 26.29%; H, 2.48%; N, 11.59%; O, 59.63%.

Identify C – F by formulae or structures, as appropriate.

Include equations, any changes in oxidation number, and working.