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Question 1
Vanadium(V) oxide acts as a catalyst in the oxidation of sulfur dioxide in the Contact process. |
a) | State the meaning of the term heterogeneous as applied to catalysts.
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b) | Give two equations to describe how V2O5 acts as a catalyst in this process.
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c) | Explain why V2O5 can be described as a catalyst in this reaction.
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d) | Fe2+ ions catalyse the reaction between iodide and peroxodisulfate ions: S2O82-(aq) + 2I-(aq) ➔ 2SO42-(aq) + I2(aq) |
Explain what type of catalysis is occuring this reaction.
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Question 2
Ethanedioic acid, (COOH)2, is the active ingredient in a spray to treat infections of the outer ear. A chemist carries out a redox titration using aqueous cerium(IV) sulfate, Ce(SO4)2(aq), to determine the percentage, by mass, of ethanedioic acid in the spray. In the titration, Ce4+(aq) ions oxidise ethanedioic acid in acidic conditions, as shown by the equation below 2Ce4+(aq) + (COOH)2(aq) → 2Ce3+(aq) + 2CO2(g) + 2H+(aq) Ce4+(aq) ions have a yellow colour. Ce3+(aq) ions are colourless. Dilute sulfuric acid is added to 5.00 g of the spray to form a colourless solution which is made up to 250.0 cm3 with distilled water. 25.00 cm3 of this solution is titrated with 1.00 x 10-2 moldm-3 Ce(SO4)2 from the burette. The titration is repeated until concordant titres are obtained. The mean titre is 22.25 cm3.
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a) | What colour change would the chemist observe at the end point?
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b) | Calculate the percentage, by mass, of ethanedioic acid, (COOH)2, in the spray. Give your answer to 3 significant figures.
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Question 3
A chemist uses the following procedure to analyse iron tablets containing iron in the form of iron(II) sulfate, FeSO4.
The overall equation for the reaction occurring in the titration is: MnO4-(aq) + 8H+(aq) + 5Fe2+(aq) ⇌ Mn2+(aq) + 4H2O(l) + 5Fe3+(aq)
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The table below shows some standard electrode potential data. |
a) | Using data in the table, explain why the chemist used sulfuric acid and not hydrochloric acid in their titration.
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b) | Suggest why this titration does not require the addition of an indicator.
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c) | State the colour change at the end-point of this titration.
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d) | The chemist decides to take burette readings from the top of the meniscus rather than from the bottom. Explain the effect of this, if any, on the titre values.
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e) | The chemist's titration readings are shown in the table below. Complete the table.
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f) | Use the titration results in part e) and information from the procedure to calculate the mass of FeSO4 in 1 iron tablet. Give your answer to 3 significant figures.
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Question 4
Some transition metals and their compounds act as catalysts. The catalysis can be classified as heterogeneous or homogeneous.
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a) | Complete the table below to indicate the type of catalysis in each reaction.
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b) | The oxidation of C2O42- ions by MnO4- ions in acidic solution is an example of a reaction that is autocatalysed.
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State the meaning of the term autocatalysed.
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c) | Write 2 equations to show how the autocatalyst, Mn2+, is involved in this oxidation of C2O42- ions.
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Question 5
This question look at the ions and complexes of cobalt. An octahedral complex ion Y, C9H30N6Co3+, exists as two optical isomers. In complex ion Y, Co3+ is bonded to three molecules of a bidentate ligand L.
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a) | Write the molecular formula of the bidenitate ligand L.
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The diagram below shows the skeletal formula of L. |
b) | Explain how L is able to act as a bidentate ligand.
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c) | Draw a diagram that shows the shape of the complex ion Y and shows the type of bond between the ligand L and the cobalt.
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d) | The compounds [Co(NH3)5Br]SO4 and [Co(NH3)5SO4]Br are structural isomers.
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Define the term structural isomer.
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e) | What is the oxidation number of cobalt in [Co(NH3)5Br]2+? A +1 B +2 C +3 D +4
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Question 6
Ammonium hexachloroplatinate, (NH4)2PtCl6, is a complex of platinum used in platinum plating. Ammonium hexachloroplatinate contains the hexachloroplatinate ion.
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a) | Draw a 3D diagram to show the shape of a hexachloroplatinate ion. On your diagram, show:
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b) | Platin, Pt(NH3)2Cl2, is a neutral complex of platinum(II).
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Explain why Pt(NH3)2Cl2 has no overall charge.
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Pt(NH3)2Cl2, displays cis-trans isomerism.
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c) | Draw the structure of cis-platin. State its shape and give a value of the Cl-Pt-Cl bond angle.
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d) | The use of cis-platin can cause side effects so oxaliplatin has been developed. The structure of oxaliplatin is shown below.
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Draw the structures of the two bidentate ligands in oxaliplatin.
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Question 7
Steel pipelines carrying natural gas can corrode to form ‘green rust’, Fe(OH)2. After some time, green rust can change into ‘black rust’ via the equation shown below. 3Fe(OH)2 ➔ Fe2+Fe3+2O4 + H2 + 2H2O
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a) | Use oxidation states to show that this is a redox reaction.
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b) | If seawater is present, the green rust is often oxidised to [FeCl4]- ions. Draw diagrams to show two possible shapes for [FeCl4]-. Name the shapes.
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c) | State the type of bonding between the chloride ligands and the iron ion in [FeCl4]-.
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d) | Cu+ also forms complexes with chloride ligands. One example is the colourless complex [CuCl2]-. Explain why [CuCl2]- ions are colourless.
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Question 8
The complex [Co(NH3)4Cl2]+ shows isomerism. |
a) | Suggest the type of isomerism shown in [Co(NH3)4Cl2]+ and draw 3D structures of the two isomers.
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b) | The diagram below shows the structure of ethane-1,2-diamine, en. en is an example of a bidentate ligand. |
Explain what is meant by the term bidentate ligand.
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c) | [Cr(en)2Cl2]+ shows geometrical and optical isomerism. Complete the 3D diagrams to show the 3 stereoisomers of [Cr(en)2Cl2]+.
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d) | Using the model answer diagram, give the letters of the two isomers of [Cr(en )2Cl2]+ which show optical isomerism.
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e) | Using the model answer diagram, give the letter of the isomer which has no overall dipole moment.
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Question 9
a) | Explain what is meant by the term transition element.
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b) | Draw electrons in the boxes below to show the electronic configurations of Cu, Cu+ and Cu2+.
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c) | Complete the table by predicting the appropriate metal ions, co-ordination numbers, formulae and charges for the complexes A-D.
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Question 10
Transition metals have characteristic properties due to their electron arrangements.
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a) | Give two characteristic properties of transition metals.
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b) | Give the electronic configurations of a chromium atom, a Cr2+ ion and a Cr3+ ion.
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c) | Explain why chromium has variable oxidation states.
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Question 11
Ethanal is oxidised to ethanoic acid by oxygen. The equation for this reaction is: 2CH3CHO + O2 ➔ 2CH3COOH This redox reaction is slow at room temperature but speeds up in the presence of cobalt compounds.
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a) | Explain why a cobalt compound is able to act as a catalyst for this process.
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b) | In the Haber process, iron acts as a heterogeneous catalyst.
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State the meaning of the term heterogeneous.
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c) | Write 2 equations to show how vanadium(V) oxide acts as a catalyst in the Contact process.
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d) | Give a reason why impurities in the reactants can cause problems in processes that use heterogeneous catalysts.
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Question 12
a) | Explain why complexes formed from transition metal ions are coloured.
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b) | This diagram represents the energy change that occurs when a d electron in a transition metal ion is excited by visible light.
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Give the equation that relates the energy change ΔE to the Planck constant h, the speed of light in a vacuum c and the wavelength of the visible light λ.
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c) | Use this equation and information in the diagram to calculate a value for the wavelength of the visible light, in nm. Give your answer to the nearest integer. The speed of light c = 3.00 x 108 m s-1 The Planck constant h = 6.63 × 10-34 J s.
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d) | The energy change shown in the diagram represents the energy of green light and results in a solution that appears violet. Violet light has a higher frequency than green light.
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Suggest how the energy change, ΔE, will differ for a transition metal ion that forms a green solution. Explain your answer.
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e) | State 3 different features of transition metal complexes that cause a change in the value of ΔE.
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