AQA A Level Chemistry

Topic Questions

A LevelChemistryAQATopic Questions6. Advanced Inorganic Chemistry (A Level only)6.2 Transition Metals (A Level only)

6.2 Transition Metals (A Level only)

DownloadView
Easy
Medium
Hard
Easy
Medium
Hard
1a2 marks

Transition metals can form complex ions where ligands are coordinately bonded to the central metal ion.

State the meaning of the terms ligand and bidentate with respect to transition metal complexes.

How did you do?

1b2 marks

Transition metals are located in the d-block of the periodic table.

i)
State the electron configuration of V2+.

ii)

Explain, using the electron configuration, why scandium is found in the d-block of the periodic table but not classed as a transition metal.

How did you do?

1c2 marks

Prussian Blue, Fe4[Fe(CN)6]3, is a dark blue pigment used in painting and dyeing. 

Prussian Blue is formed when an iron (III) salt is added to a solution containing the complex ion [Fe(CN)6]4−.

i)
State the oxidation state of Fe in [Fe(CN)6]4− ion.

ii)
State the name of the shape and bond angle between the ligands in [Fe(CN)6]4− ion.

How did you do?

1d3 marks

Iron and zinc are in the d-block of the Periodic Table.

Iron (II) ions, [Fe(H2O)6]2+, form a pale green solution but zinc ions, [Zn(H2O)6]2+, form a colourless solution.

i)
Write the electron configuration of Zn2+ ion.

ii)
Explain, with reference to your answer from part (i), why zinc ions are colourless.

How did you do?

Did this page help you?

2a1 mark

A complex ion contains one Fe3+ ion, four ammonia molecules and two chloride ions.

State the formula of this complex ion.

How did you do?

2b2 marks

Transition metals have characteristic properties. One of these properties is that they form coloured ions.

State two other properties that transition metals or their ions exhibit.

How did you do?

2c2 marks

Transition metals can be used as successful catalysts in a range of reactions.

i)
State what is meant by the term homogeneous catalyst.

ii)
State what is meant by the term autocatalysis.

How did you do?

2d2 marks

Transition metals can form complexes with different ligands.

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

CO         H2O         SCN-          H2

How did you do?

Did this page help you?

3a3 marks

Transition metals can form complex ions which contain bidentate ligands.

i)

State the formula of a bidentate ligand.
EDTA4- is an example of a multidentate ligand.

ii)

Write an equation showing the reaction when a solution containing [Fe(H2O)6]2+ ions is treated with a solution containing EDTA4– ions.

iii)
State what happens to the entropy value of this reaction.

How did you do?

3b2 marks

Blood carries oxygen around the body due to the presence of haemoglobin. Haemoglobin consists of a haem molecule that has a central metal iron (II) ion which can bind to oxygen gas.

Figure 1

Ah4W~JqV_1

Explain why carbon monoxide bonding to haemoglobin can be deadly.

How did you do?

3c1 mark

The equilibrium below shows the ligand substitution of a water molecule by oxygen in the pulmonary alveoli.

Hb(H2O) + O2 ⇋ Hb(O2) + H2O

Write the overall equilibrium constant, Kc,  for this reaction.

How did you do?

3d2 marks

The [Ni(NH3)4Cl2]+ ion exists as two isomers. One geometric isomer is shown in Figure 2 below.

Figure 2

urkOQfis_2

Draw the structure of the other isomer and state the type of isomerism.

How did you do?

Did this page help you?

4a2 marks

The reaction between iodide ions and peroxodisulfate ions is catalysed by iron (II) ions.

2I- + S2O82- → I2 + 2SO42-

i)
Give a reason why the reaction between iodide ions and peroxodisulfate ions has a high activation energy and is therefore very slow without a catalyst.

ii)
Explain how the iron (II) ions catalyse this reaction.

How did you do?

4b1 mark

The element vanadium exists in a variety of oxidation numbers in its compounds.

Calculate the oxidation number of vanadium in the compound NH4VO3.

How did you do?

4c1 mark

The solid compound V2O5 is used as a heterogeneous catalyst in the Contact Process to speed up the reaction between oxygen and sulfur dioxide gas.

Define the term heterogeneous.

How did you do?

4d2 marks

Write two equations to show how vanadium (V) oxide acts as a catalyst in the Contact Process as discussed in part (c).

How did you do?

Did this page help you?

5a1 mark

Ammonia can react with transition metal complexes as a Lewis base or Brønsted-Lowry base.

Define the term Lewis base.

How did you do?

5b3 marks
i)

Write an equation to show the reaction of dropwise dilute ammonia with aqueous [Fe(H2O)6]2+.

ii)
State whether in the reaction, ammonia is reacting as Lewis base or Brønsted-Lowry base in part (i).

iii)

State what you would observe for this reaction.

How did you do?

5c1 mark

Transition metals can form different coloured complexes. The colour of the complex formed can be represented using the relationship ΔE = hv.

State what h and v represent in the equation.

How did you do?

5d3 marks

State three factors that affect the value of ΔE.

How did you do?

Did this page help you?

1a4 marks

This question is about transition metals and transition metal complexes.

When chromium (III) sulfate dissolves in water, a green solution containing the [Cr(H2O)6]3+ ion forms.

i)
State the bond angles found in this complex ion.

ii)
Explain why the chromium (III) complex ion is coloured.

How did you do?

1b3 marks

This question is about transition metals and transition metal complexes.

The ligand ethylenediaminetetraacetate, EDTA4−, is shown in Figure 1.

Figure 1

1ddFxNzA_18

When a solution of EDTA4− is added to a solution of [Cr(H2O)6]3+ ions, a new complex ion is formed.

[Cr(H2O)6]3+ + EDTA4-   ⇌  [Cr(EDTA)]- + 6H2O

The equilibrium constant for this equilibrium is 2.51 × 1023  mol−1dm3.

By considering the equilibrium for this reaction and changes in entropy, comment on the value of the equilibrium constant. No calculations are required.

How did you do?

1c3 marks

Compound I is a complex with the empirical formula CoN4H12Cl3.

The formula of compound I contains one chloride ion and a complex ion J, which has two stereoisomers.

Draw and label the three-dimensional structures of the two stereoisomers of complex ion J. Include the charge of the complex ion in your diagrams.

How did you do?

1d3 marks

Chromium (III) picolinate, shown in Figure 2, is a neutral complex that can be prepared from the weak acid, picolinic acid.

Figure 2

AQ4CbKxZ_20

Chromium (III) picolinate is used in tablets as a nutritional supplement for chromium.

i)
Draw the structure of the ligand in chromium (III) picolinate.

ii)

A typical tablet of chromium (III) picolinate contains 200 μg of chromium.

Calculate the mass, in g, of chromium (III) picolinate in a typical tablet.

Give your answer to three significant figures.

How did you do?

Did this page help you?

2a5 marks

Chromium is in the d-block of the Periodic Table.

Hydrated chromium (II) ions react with ethanedioate ions, C2O42-, to form geometric isomers.

[Cr(H2O)6]2+ +2C2O42- ⇌ [Cr(C2O4)2(H2O)2]2- + 4H2O

i)
Draw a structure of the cis [Cr(C2O4)2(H2O)2]2– ion, showing all of the bonds.

ii)
Explain, in terms of entropy, why this reaction is feasible.

How did you do?

2b3 marks

Table 1 below shows the first and second ionisation energies of nickel, copper and zinc.

Table 1

Element

1st ionisation energy / kJ mol-1

2nd ionisation energy / kJ mol-1

Ni

737

1753

Cu

746

1958

Zn

906

1733


The values for the first ionisation energies of copper and nickel are similar, but the values of the second ionisation energies are significantly different.

i)
Explain how these data give evidence for the electronic configuration of a copper atom.

ii)
Suggest why you might expect the third ionisation energies of the three elements to increase from nickel to zinc.

How did you do?

2c5 marks

The equilibrium reaction for the transport of oxygen by haemoglobin (Hb) in blood can be represented as shown.

Hb (aq) + O2 (aq) ⇌ HbO2 (aq)

i)
Explain how ligand substitution reactions allow haemoglobin to transport oxygen in blood.

ii)

Write an expression for the equilibrium constant, Kc, for the equilibrium involved in the transport of oxygen by haemoglobin.
Use the simplified species in the equation.

iii)

In the presence of carbon monoxide, less oxygen is transported in the blood.
Explain why, in terms of bond strength and Kc.

How did you do?

2d2 marks

Iron and zinc are in the d-block of the Periodic Table.

Iodide ions, I–, react with peroxodisulfate (VI) ions, S2O82- as shown in the reaction below.

2I- (aq) + S2O82- (aq) →  I2 (aq) + 2SO42- (aq)

This reaction is catalysed by iron (II) ions, Fe2+(aq).

Write two ionic equations to show how iron (II) ions act as a catalyst in this reaction.

State symbols are not required.

How did you do?

Did this page help you?

3a6 marks

Prince’s metal is a type of brass alloy that is used as imitation gold due to its yellow colour.

The copper content of a 5.00 g sample of Prince’s metal was analysed.

As part of the reaction process, copper ions are reacted with excess potassium iodide.

2Cu2+ + 4I- → 2CuI + I2

The iodine formed is analysed by titration with sodium thiosulfate.

I2 + 2S2O32- → 2I- + S4O62-

The sample containing iodine was diluted to 250 cm3 and then 10.0 cm3 aliquots were titrated with 0.100 mol dm-3 sodium thiosulfate solution. The mean titre used was 22.65 cm3.

i)
Calculate the percentage of copper, by mass, in the sample of Prince’s metal.

ii)

The burette used had a margin of error of ±0.15 cm3.
Calculate the percentage error in the burette for the titration.

How did you do?

3b3 marks

A complex of cobalt has the following composition by mass:

Co, 21.98%; N, 31.35%; H, 6.81%; Cl, 39.86%

i)
Calculate the empirical formula of this complex.

ii)

The formula of this cobalt complex can be expressed in form [Co(L)m]x+(Cl−)n.
Suggest the chemical formula of [Co(L)m]x+.

How did you do?

3c5 marks

EDTA4- is very soluble in water and is a multidentate ligand which can react with iron (II) ions to form complex ions. The concentration of iron (II) ions in a sample of river water was determined by colorimetry to be 7.84 × 10−5 mol dm−3.

This result was checked by titrating a sample of the water with a solution containing EDTA4−(aq) ions.

The EDTA4−(aq) had a concentration of 1.50 × 10−3 mol dm−3.

i)
Write an equation for the reaction between [Fe(H2O)6]2+ and EDTA4− ions.

ii)
Calculate the volume of the EDTA4− solution needed to react with a 30.0 cm3 sample of the water.

iii)
Justify whether this titration will give an accurate value for the concentration of iron (II) ions. If necessary, suggest a practical step that would improve the accuracy.

How did you do?

3d5 marks

1,2-diaminoethane is a bidentate ligand which can form a complex with [Co(NH3)4(H2O)2]2+. In this reaction only the ammonia molecules are replaced.

i)
Write an equation for this reaction.

ii)
Suggest why the enthalpy change for the reaction is approximately zero.

iii)

Explain why the reaction proceeds despite having an enthalpy change that is approximately zero.

How did you do?

Did this page help you?

4a2 marks

State and draw the number of stereoisomers that Co(H2NCH2CH2NH2)2Cl2 can form?

How did you do?

4b1 mark

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 Stage 1 to 250.0 cm3 in a volumetric flask.
  3. The student then titrated 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.

How did you do?

4c5 marks

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

Give your answer to 3 significant figures.

How did you do?

4d1 mark

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

Table 1 shows the information taken from the labels of two iron supplements, A and B.

Table 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.

How did you do?

Did this page help you?

5a4 marks

Fe2+ ions can be used to test for NO3− ions.

In this test, aqueous iron (II) sulfate is added to a solution containing NO3− ions, followed by slow addition of concentrated sulfuric acid. The sulfuric acid forms a layer below the aqueous solution.

In the presence of NO3− ions, a brown ring forms between the two layers.

Two reactions take place.

Reaction 1:

In the acid conditions Fe2+ ions reduce NO3- ions to NO. Fe2+ ions are oxidised to Fe3+ ions and water also forms.

Reaction 2:

A ligand substitution reaction of [Fe(H2O)6]2+ takes place in which one NO ligand exchanges with one water ligand. A deep brown complex ion forms as the brown ring.

i)
Construct equations for these two reactions.

ii)
State the type of reaction that occurs in reaction 1 and reaction 2.

How did you do?

5b2 marks

When an acidified solution of potassium manganate (VII) is reacted with a sample of sodium ethanedioate, the reaction is quite slow initially for the purple colour to decolourise.

Write the overall equation for the reaction between manganate (VII) ions and ethanedioate ions in acidic solution.

How did you do?

5c3 marks

Explain how the use of a colorimeter can be used to measure the increasing concentration of manganate ions formed in part (b).

How did you do?

5d1 mark

Iron is a transition element that forms a number of ions with the iron in different oxidation states.

State the shorthand electron configuration of the iron cation that can form the complex ion [Fe(CN)6]4−.

How did you do?

Did this page help you?

1a6 marks

This question is about the transition metal copper.

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

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

How did you do?

1b5 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.

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

iii)

Draw a diagram to show the structure of the complex ion formed and name the shape it takes.

iv)
State the change in coordination number.

How did you do?

1c4 marks

[Cu(H2O)6]2+  absorbs red light (700 nm) and the solution appears blue.

i)

Give the equation which relates the energy change to the Planck constant, h, and the frequency of the visible light.

ii)

Calculate a value for the energy in J associated with this wavelength of light. The Planck constant h = 6.63 x 10-34J s and c = 3 x 108 m s-1.

iii)

State two different features of a transition metal complex which cause a change in the energy change value.

How did you do?

1d5 marks

EDTA is a multidentate ligand with a wide range of applications in both medicine and Industry.

Figure 1

NmxXl7Bk_4

When added to a solution containing [Ni(H2O)6]2+ ions a ligand substitution reaction will occur:

[Ni(H2O)6]2+ + EDTA4- → [NiEDTA]2- + 6H2O

i)
EDTA4- is a chelating ligand.  Explain this term.

ii)
Explain why this ligand substitution reaction occurs.

iii)
State the coordination number of the two complexes [Ni(H2O)6]2+ and [NiEDTA]2-.

How did you do?

Did this page help you?

2a7 marks

12.2 g of hydrated iron (II) sulfate, FeSO4.xH2O were dissolved in acidic solution and made up to a volume of 500 cm3.  A 25.0 cm3 sample of this solution was titrated against 0.0200 mol dm-3 potassium manganate (VII) solution.  21.95 cm3 of this solution were required.

i)
Give an equation for the reaction between iron (II) ions and manganate ions.

ii)
State the colour change that occurs at the end-point.

iii)
Calculate the value of x in FeSO4.xH2O.

How did you do?

2b8 marks

Complexes of [Pt(NH3)2Cl2] and [Ni(H2NCH2CH2NH2)3]2+ exhibit different forms of stereoisomerism.

i)
State the type of stereoisomerism shown by each of the complexes.

ii)
Draw the isomers of each complex.

iii)
Give a use of an isomer of [Pt(NH3)2Cl2].

iv)
Explain why [Ni(H2NCH2CH2NH2)3]2+ has a 2+ charge overall.

How did you do?

2c7 marks

Transition metals and their compounds are important catalysts.

i)
Explain the term heterogeneous catalyst.

ii)
Name the heterogeneous catalyst used in the Haber Process.

iii)
Heterogeneous catalysts work by chemisorption. Explain this process.

iv)
Explain why heterogeneous catalysts can become ineffective as a result of impurities. 

How did you do?

2d7 marks

The reaction of manganate (VII) ions with ethanedioate ions is initially very slow. However, the reaction is catalysed by manganese (II) ions which are formed in the reaction.

i)

Give an equation for the reaction between manganate (VII) ions and ethanedioate ions using the half equations below.

MnO4- + 8H+ + 5e- → 2Mn2+ + 4H2O

C2O42- → 2CO2 + 2e-

ii)
Explain why the reaction can be monitored using colorimetry.

iii)

Sketch a graph of concentration of manganate (VII) ions against time. Explain the shape of the graph.

How did you do?

Did this page help you?

3a4 marks

Complete Table 1 below giving the formula, oxidation number and colour in solution of some vanadium ions.

Table 1

ION

OXIDATION NUMBER

AQUEOUS COLOUR

V2+

 

 

 

 

Yellow

VO2+

 

 

 

+3

 

How did you do?

3b3 marks

Vanadium (V) oxide is the catalyst used in the contact process as shown by the reactions:

SO2 + V2O5 → SO3 + V2O4

V2O4 + begin mathsize 16px style 1 half end styleO2 → V2O5

i)
Using the equations, write an overall equation for the reaction.

ii)
Explain using the equations why V2O5 is a catalyst.

iii)
Explain why V2O5 is able to act as a catalyst in this reaction.

How did you do?

3c5 marks

When iron (II) compounds dissolve in water they form [Fe(H2O)6]2+, the hexaaquairon (II) complex.

i)
State the full electronic configuration of an iron (II) ion.

ii)
Predict the shape, and the bond angle of the hexaaquairon (II) complex.

iii)

The complex [Fe(H2O)6]2+ will react with sodium carbonate solution. Give an observation and an equation for the reaction with carbonate ions.

How did you do?

3d6 marks

Ligand and coordination number are common terms related to transition metals and their complexes.

i)
Explain the meaning of the terms ligand and coordination number. 

ii)

When ammonia (NH3) is added to [Co(H2O)6]2+ a ligand substitution reaction takes place and a new complex is formed, [Co(NH3)6]2+. Give an equation for this reaction.

iii)

[Co(H2O)6]2+ is pink and [Co(NH3)6]2+ is yellow.  Explain why the two complexes have different colours.  

How did you do?

Did this page help you?

4a4 marks

Aqueous Iron (II), Fe2+ and iron (III), Fe3+ ions catalyse the reaction between peroxodisulfate ions, S2O82-and iodide ions, I-. It forms sulfate (VI) ions SO42- and iodine, I2 and is an example of homogeneous catalysis.

i)
Explain what is meant by the term homogeneous catalysis.

ii)

Give an equation for the conversion of S2O82- ions into SO42- ions using I- ions and explain why it is slow.

iii)

Explain how the iron (II), Fe2+ or iron (III), Fe3+ ions catalyse the reaction.

How did you do?

4b4 marks

The complex [Ni(H2O)6]2+ reacts with 1,2-diaminoethane according to the equation:

[Ni(H2O)6]2+ + 3H2NCH2CH2NH2 → [Ni(H2NCH2CH2NH2)3]2+ + 6H2O

i)
State and explain the change in coordination number during this reaction.

ii)
Predict the sign of ΔS for the reaction. Justify your prediction.

How did you do?

4c5 marks

People with anaemia are often advised to take iron tablets which contain hydrated iron (II) sulfate, FeSO4.6H2O.  The composition of these tablets can be analysed by titration with acidified potassium manganate (VII) solution. 

6 g of tablets were crushed, dissolved in deionised water and made up to a volume of 250 cm3 in a volumetric flask.  25.0 cm3 samples of the iron tablet solution were titrated with 0.0200 mol dm-3 potassium manganate (VII) solution and the average titre value was 22.4 cm3.

Use this information to calculate the percentage of FeSO4.6H2O in the tablets.

How did you do?

4d3 marks

In humans, oxygen from the lungs dissolves in the blood and enters red blood cells where it forms a complex with haemoglobin.  A molecule of haemoglobin consists of four subunits, each containing an iron-haem complex, as shown in Figure 1 below.

Figure 1

0PuzBs6__7

i)
Explain the role of iron (II) in haemoglobin.

ii)

With reference to iron (II) in haemoglobin, explain why breathing carbon monoxide can result in death.

How did you do?

Did this page help you?

5a4 marks

Reduction potentials can be used to predict the feasibility of reactions. Consider the two half equations below:

VO2+ + 2H+ + e- → V3+ + H2O             E = +0.34V

Zn2+ + 2e- → Zn                                   E = -0.76V

i)

Give an ionic equation for the reaction between zinc and the oxovanadium (IV) VO2+ ions.

ii)
Calculate the EMF of this reaction.
iii)
Predict the colour change which would be observed.

How did you do?

5b8 marks

EDTA can sequester metal ions in a mixture by forming a stable complex that prevents the metal ions from reacting with other molecules or ions in the mixture.  The reaction is used in medicine to sequester calcium ions to prevent them from participating in clot formation.  It can also be used to determine the concentration of calcium compounds in hard water.

Figure 1

0PuzBs6__7

i)
Give an equation to represent the reaction between [Ca(H2O)6]2+ and EDTA.

ii)
Explain why the entropy value for the reaction is positive.

iii)

A solution of calcium chloride was diluted by placing 25.0 cm3 into a volumetric flask and volume made up to 250.0 cm3 using deionised water.  25.0 cm3 of this solution was titrated with 0.0500 mol dm-3 EDTA solution and the average titre was found to be 12.7 cm3.

Calculate the concentration of the original calcium chloride solution in g dm-3.

How did you do?

5c4 marks

Tollens’ reagent is used to distinguish between aldehydes and ketones.  It can also be referred to as the diamminesilver (I) complex.

i)
Write the formula of the complex.

ii)
Draw the displayed structure of the complex.

iii)
Name the shape the complex takes and give a value for the bond angle.

How did you do?

5d6 marks

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

i)
Deduce the oxidation state of cobalt in this complex and explain your answer.

ii)

Draw and label each isomer of the complex.

How did you do?

Did this page help you?