Q1.
The following scheme shows some reactions of chromium compounds in aqueous solution.
(a)
Identify the grey-green precipitate A and the gas B formed in Reaction 1. Write an equation
for this reaction.
Precipitate A .................................................................................................
Gas B ...........................................................................................................
Equation .......................................................................................................
......................................................................................................................
(3)
(b)
(i)
Identify a reagent for Reaction 2.
.............................................................................................................
(ii)
Deduce the oxidation state of chromium in CrO
.............................................................................................................
(iii)
Identify a reagent needed for Reaction 3. Write a half-equation for the conversion of
[Cr(OH)6]3– into CrO
Reagent ..............................................................................................
Half-equation …...................................................................................
.............................................................................................................
(4)
Page 1 of 44
(c)
(i)
Draw the structure of the chromium-containing species C formed in Reaction 5.
Indicate the charge on species C.
(ii)
Explain, by reference to the changes in bonding, why the enthalpy change, ∆H, in
Reaction 5 is close to zero.
.............................................................................................................
.............................................................................................................
(iii)
Explain why the free-energy change, ∆G, for Reaction 5 is negative.
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
(7)
(d)
Identify the chromium-containing species present in the blue solution D formed in
Reaction 6 and state the role of zinc in its formation.
Chromium-containing species .....................................................................
Role of zinc...................................................................................................
(2)
(e)
Two organic compounds are formed in Reaction 7. One of these compounds has a low
boiling point and can be distilled readily from the reaction mixture. The other compound
has a higher boiling point and is the main organic product formed when the reaction
mixture is refluxed.
(i)
Identify the organic product which has a low boiling point.
.............................................................................................................
(ii)
Identify the main organic product formed when the mixture is refluxed.
.............................................................................................................
(2)
(Total 18 marks)
Page 2 of 44
Q2.
Transition metal ions can act as homogeneous catalysts in redox reactions. For example,
iron(II) ions catalyse the reaction between peroxodisulfate (S2O82–) ions and iodide ions.
(a)
State the meaning of the term homogeneous.
......................................................................................................................
(1)
(b)
Suggest why ions from s block elements do not usually act as catalysts.
......................................................................................................................
......................................................................................................................
(1)
(c)
Write an equation for the overall reaction that occurs, in aqueous solution, between S2O82–
ions and I– ions.
......................................................................................................................
(1)
(d)
Give one reason why, in the absence of a catalyst, the activation energy for the reaction
between S2O82– ions and I– ions is high.
......................................................................................................................
......................................................................................................................
(1)
(e)
Write two equations to show how Fe2+ ions can catalyse the reaction between S2O82– ions
and I– ions. Suggest one reason why the activation energy for each of these reactions is
low.
Equation 1 ...................................................................................................
Equation 2 ...................................................................................................
Reason ........................................................................................................
......................................................................................................................
(3)
(f)
Explain why Fe3+ ions are as effective as Fe2+ ions in catalysing this reaction.
......................................................................................................................
......................................................................................................................
(1)
(Total 8 marks)
Page 3 of 44
Q3.
(a)
Explain why the reaction between sodium ethanedioate, Na2C2O4, and potassium
manganate(VII) in acidified aqueous solution is initially slow but gradually increases in rate.
Write equations to illustrate your answer.
(6)
(b)
State what is meant by the term active site as applied to a heterogeneous catalyst. Explain
how the number of active sites can be increased for a given mass of catalyst. The
efficiency of a heterogeneous catalyst often decreases during use. Explain, using a
specific example, why this happens.
(4)
(Total 10 marks)
Q4.
Three characteristic properties of transition metals are complex formation, coloured ions
and catalytic activity.
(a)
State the feature of transition metals that gives rise to these characteristic properties.
......................................................................................................................
(1)
(b)
State a fourth characteristic property of transition metals.
......................................................................................................................
(1)
(c)
For each of the following shapes of complex, identify an appropriate example by drawing
its structure.
(i)
a linear complex
(1)
(ii)
a square planar complex
(1)
Page 4 of 44
(iii)
a tetrahedral complex
(1)
(d)
The chemical industry makes use of the catalytic activity of transition metal compounds.
For example, vanadium(V) oxide is used as a heterogeneous catalyst in the Contact
Process.
(i)
Write an equation for the overall reaction in the Contact Process.
.............................................................................................................
(1)
(ii)
Explain the meaning of the term heterogeneous as applied to a catalyst.
.............................................................................................................
(1)
(iii)
Write two equations to illustrate how vanadium(V) oxide acts as a catalyst in the
Contact Process.
Equation 1 ...........................................................................................
Equation 2 ...........................................................................................
(2)
(iv)
Suggest what is done to a heterogeneous catalyst such as vanadium(V) oxide to
maximise its efficiency and how this is achieved.
.............................................................................................................
.............................................................................................................
.............................................................................................................
(2)
(e)
The porphyrin ring is a multidentate ligand that is found in living systems complexed with
iron(II) ions in haemoglobin and with cobalt(II) ions in vitamin B12
(i)
Give the meaning of the term multidentate.
.............................................................................................................
.............................................................................................................
(1)
Page 5 of 44
(ii)
A porphyrin ring can be represented by the symbol PR. It reacts with aqueous iron(II)
ions as shown in the equation below.
The enthalpy change for this reaction is approximately zero.
PR(aq) + [Fe(H2O)6]2+(aq) → [FePR(H2O)2]2+(aq) + 4H2O(l)
Explain why the free-energy change for this reaction is negative.
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
(2)
(iii)
In vitamin B12 the cobalt(II) ion is co-ordinated to a porphyrin ring, a cyanide
(CN–) ion and an additional unidentate ligand. The cyanide ion is very toxic.
Predict the co-ordination number of the cobalt ion in vitamin B12
Suggest why vitamin B12 is not toxic.
Co-ordination number .....................................................................................
Reason why vitamin B12 is not toxic
.............................................................................................................
.............................................................................................................
(2)
(Total 16 marks)
Page 6 of 44
Q5.
Iron is an important element in living systems. It is involved in redox and in acid–base
reactions.
(a)
Explain how and why iron ions catalyse the reaction between iodide ions and S2O82– ions.
Write equations for the reactions that occur.
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(Extra space) ................................................................................................
......................................................................................................................
......................................................................................................................
(5)
(b)
Iron(II) compounds are used as moss killers because iron(II) ions are oxidised in air to
form iron(III) ions that lower the pH of soil.
(i)
Explain, with the aid of an equation, why iron(III) ions are more acidic than iron(II) ions
in aqueous solution.
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
(3)
Page 7 of 44
(ii)
In a titration, 0.321 g of a moss killer reacted with 23.60 cm3 of acidified
0.0218 mol dm–3 K2Cr2O7 solution.
Calculate the percentage by mass of iron in the moss killer. Assume that all of the
iron in the moss killer is in the form of iron(II).
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
(5)
(c)
Some sodium carbonate solution was added to a solution containing iron(III) ions.
Describe what you would observe and write an equation for the reaction that occurs.
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(3)
(Total 16 marks)
Page 8 of 44
Q6.
This question is about copper chemistry.
(a)
Aqueous copper(II) ions [Cu(H2O)6]2+(aq) are blue.
(i)
With reference to electrons, explain why aqueous copper(II) ions are blue.
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
(Extra space) ......................................................................................
.............................................................................................................
.............................................................................................................
(3)
(ii)
By reference to aqueous copper(II) ions, state the meaning of each of the three
terms in the equation ΔE = hv.
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
(Extra space) .......................................................................................
.............................................................................................................
.............................................................................................................
(3)
Page 9 of 44
(iii)
Write an equation for the reaction, in aqueous solution, between [Cu(H2O)6]2+ and an
excess of chloride ions.
State the shape of the complex produced and explain why the shape differs from that
of the [Cu(H2O)6]2+ ion.
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
(Extra space) .......................................................................................
.............................................................................................................
.............................................................................................................
(3)
(b)
Draw the structure of the ethanedioate ion (C2O42–).
Explain how this ion is able to act as a ligand.
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(2)
Page 10 of 44
(c)
When a dilute aqueous solution containing ethanedioate ions is added to a solution
containing aqueous copper(II) ions, a substitution reaction occurs. In this reaction four
water molecules are replaced and a new complex is formed.
(i)
Write an ionic equation for the reaction. Give the co-ordination number of the
complex formed and name its shape.
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
(4)
(ii)
In the complex formed, the two water molecules are opposite each other.
Draw a diagram to show how the ethanedioate ions are bonded to a copper ion and
give a value for one of the O–Cu–O bond angles. You are not required to show the
water molecules.
(2)
(Total 17 marks)
Q7.
Transition metals and their complexes have characteristic properties.
(a)
Give the electron configuration of the Zn2+ ion.
Use your answer to explain why the Zn2+ ion is not classified as a transition metal ion.
Electron configuration ..................................................................................
Explanation ..................................................................................................
......................................................................................................................
(2)
Page 11 of 44
(b)
In terms of bonding, explain the meaning of the term complex.
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(2)
(c)
Identify one species from the following list that does not act as a ligand. Explain your
answer.
H2
O2–
O2
CO
Not a ligand..................................................................................................
Explanation ...................................................................................................
(2)
(d)
The element palladium is in the d block of the Periodic Table. Consider the following
palladium compound which contains the sulfate ion.
[Pd(NH3)4]SO4
(i)
Give the oxidation state of palladium in this compound.
.............................................................................................................
(1)
(ii)
Give the names of two possible shapes for the complex palladium ion in this
compound.
Shape 1 ..............................................................................................
Shape 2 ..............................................................................................
(2)
(Total 9 marks)
Page 12 of 44
Q8.
Due to their electron arrangements, transition metals have characteristic properties including
catalytic action and the formation of complexes with different shapes.
(a)
Give two other characteristic properties of transition metals. For each property,illustrate
your answer with a transition metal of your choice.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(4)
(b)
Other than octahedral, there are several different shapes shown by transition metal
complexes. Name three of these shapes and for each one give the formula of a complex
with that shape.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(6)
(c)
It is possible for Group 2 metal ions to form complexes. For example, the [Ca(H2O)6]2+ ion
in hard water reacts with EDTA4– ions to form a complex ion in a similar manner to
hydrated transition metal ions. This reaction can be used in a titration to measure the
concentration of calcium ions in hard water.
(i)
Write an equation for the equilibrium that is established when hydrated calcium ions
react with EDTA4– ions.
...............................................................................................................
(1)
Page 13 of 44
(ii)
Explain why the equilibrium in part (c)(i) is displaced almost completely to the right to
form the EDTA complex.
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
(3)
(iii)
In a titration, 6.25 cm3 of a 0.0532 mol dm–3 solution of EDTA reacted completely with
the calcium ions in a 150 cm3 sample of a saturated solution of calcium hydroxide.
Calculate the mass of calcium hydroxide that was dissolved in 1.00 dm3 of the
calcium hydroxide solution.
...............................................................................................................
...............................................................................................................
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...............................................................................................................
(Extra space) ........................................................................................
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...............................................................................................................
(3)
(Total 17 marks)
Page 14 of 44
Q9.
An acidified solution of potassium manganate(VII) was reacted with a sample of sodium
ethanedioate at a constant temperature of 60 °C. The concentration of the manganate(VII) ions
in the reaction mixture was determined at different times using a spectrometer to measure the
light absorbed.
(a)
Write an equation for the reaction between manganate(VII) ions and ethanedioate ions in
acidic solution.
........................................................................................................................
........................................................................................................................
........................................................................................................................
(Extra space) .................................................................................................
........................................................................................................................
(2)
(b)
By considering the properties of the reactants and products, state why it is possible to use
a spectrometer to measure the concentration of the manganate(VII) ions in this reaction
mixture.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(2)
(c)
This reaction is autocatalysed. Give the meaning of the term autocatalyst.
Explain how the above curve indicates clearly that the reaction is autocatalysed.
Meaning of autocatalyst ................................................................................
........................................................................................................................
Explanation ....................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(3)
Page 15 of 44
(d)
Identify the autocatalyst in this reaction.
........................................................................................................................
(1)
(e)
Write two equations to show how the autocatalyst is involved in this reaction.
Equation 1 ......................................................................................................
Equation 2 ......................................................................................................
(2)
(Total 10 marks)
Q10.
This question is about cobalt chemistry.
(a)
Consider the following reaction scheme that starts from [Co(H2O)6]2+ ions.
W, X and Y are ions and Z is a compound.
For each of the reactions 1 to 4, identify a suitable reagent.
Page 16 of 44
Identify W, X, Y and Z and write an equation for each of reactions 1 to 4.
........................................................................................................................
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(Extra space) .................................................................................................
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(12)
(b)
A flue-gas desulfurisation process involves the oxidation, by oxygen, of aqueous sulfate(IV)
ions (SO3 2–) into aqueous sulfate(VI) ions (SO4 2–). This reaction is catalysed by Co2+ ions in
an acidic aqueous solution.
Write an equation for the overall reaction of sulfate(IV) ions with oxygen to form sulfate(VI)
ions.
Suggest why this overall reaction is faster in the presence of Co2+ ions.
Page 17 of 44
Suggest a mechanism for the catalysed reaction by writing two equations involving Co2+
and Co3+ ions. You will need to use H+ ions and H2O to balance these two equations.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(4)
(Total 16 marks)
Q11.
Due to their electron arrangements, transition metals have characteristic properties
including catalytic action and the formation of complexes with different shapes.
(a)
Give two other characteristic properties of transition metals. For each property,illustrate
your answer with a transition metal of your choice.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(4)
Page 18 of 44
(b)
Other than octahedral, there are several different shapes shown by transition metal
complexes. Name three of these shapes and for each one give the formula of a complex
with that shape.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(6)
(c)
It is possible for Group 2 metal ions to form complexes. For example, the [Ca(H2O)6]2+ ion
in hard water reacts with EDTA4– ions to form a complex ion in a similar manner to
hydrated transition metal ions. This reaction can be used in a titration to measure the
concentration of calcium ions in hard water.
(i)
Write an equation for the equilibrium that is established when hydrated calcium ions
react with EDTA4– ions.
...............................................................................................................
(1)
(ii)
Explain why the equilibrium in part (c)(i) is displaced almost completely to the right to
form the EDTA complex.
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
(3)
Page 19 of 44
(iii)
In a titration, 6.25 cm3 of a 0.0532 mol dm–3 solution of EDTA reacted completely with
the calcium ions in a 150 cm3 sample of a saturated solution of calcium hydroxide.
Calculate the mass of calcium hydroxide that was dissolved in 1.00 dm3 of the
calcium hydroxide solution.
...............................................................................................................
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...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
(Extra space) ........................................................................................
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...............................................................................................................
(3)
(Total 17 marks)
Q12.
Solid iron(II) ethanedioate dihydrate (FeC2O4.2H2O) has a polymeric structure.
Two repeating units in the polymer chain are shown.
Each iron ion is also bonded to
two water molecules. These are
not shown in the diagram.
(a)
Name the type of bond that is represented by the arrows.
........................................................................................................................
(1)
(b)
In terms of electrons explain how the water molecules, not shown in the diagram, form
bonds to the iron.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(2)
Page 20 of 44
(c)
Predict the value of the bond angle between the two bonds to iron that are formed by these
two water molecules.
........................................................................................................................
(1)
(d)
Iron(II) ethanedioate dihydrate can be analysed by titration using potassium manganate(VII)
in acidic solution. In this reaction, manganate(VII) ions oxidise iron(II) ions and ethanedioate
ions.
A 1.381 g sample of impure FeC2O4.2H2O was dissolved in an excess of dilute sulfuric
acid and made up to 250 cm3 of solution.
25.0 cm3 of this solution decolourised 22.35 cm3 of a 0.0193 mol dm–3 solution of
potassium manganate(VII).
(i)
Use the half-equations given below to calculate the reacting ratio of moles of
manganate(VII) ions to moles of iron(II) ethanedioate.
MnO4– + 8H+ + 5e–
Fe2+
C2O42–
Mn2+ + 4H2O
Fe3+ + e–
2CO2 + 2e–
...............................................................................................................
...............................................................................................................
...............................................................................................................
(1)
Page 21 of 44
(ii)
Calculate the percentage by mass of FeC2O4.2H2O in the original sample.
(If you have been unable to answer part (d)(i) you may assume that three moles of
manganate(VII) ions react with seven moles of iron(II) ethanedioate. This is not the
correct ratio.)
...............................................................................................................
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(5)
(Total 10 marks)
Q13.
This question is about cobalt chemistry.
(a)
Consider the following reaction scheme that starts from [Co(H2O)6]2+ ions.
W, X and Y are ions and Z is a compound.
For each of the reactions 1 to 4, identify a suitable reagent.
Page 22 of 44
Identify W, X, Y and Z and write an equation for each of reactions 1 to 4.
........................................................................................................................
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(Extra space) .................................................................................................
........................................................................................................................
........................................................................................................................
(12)
(b)
A flue-gas desulfurisation process involves the oxidation, by oxygen, of aqueous sulfate(IV)
ions (SO3 2–) into aqueous sulfate(VI) ions (SO4 2–). This reaction is catalysed by Co2+ ions in
an acidic aqueous solution.
Write an equation for the overall reaction of sulfate(IV) ions with oxygen to form sulfate(VI)
ions.
Suggest why this overall reaction is faster in the presence of Co2+ ions.
Page 23 of 44
Suggest a mechanism for the catalysed reaction by writing two equations involving Co2+
and Co3+ ions. You will need to use H+ ions and H2O to balance these two equations.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(4)
(Total 16 marks)
Page 24 of 44
M1.
(a)
A Cr(H2O)3(OH)3 (or Cr(OH)3)
1
B CO2
1
2[Cr(H2O)6]3+ +3CO32– → 2[Cr(H2O)3(OH)3] + 3CO2 +3H2O
(or gives 2Cr(OH)3 + 3CO2 + 9H2O)
1
(b)
(i)
NaOH
(or KOH)
1
(ii)
+6
(or 6 or +VI or VI)
1
(iii)
H2O2
(or Na2O2 or BaO2)
1
[Cr(OH)6]3– + 2OH– → CrO42– +4H2O + 3e–
(or [Cr(OH)6]3–→ CrO42– +2H2O + 2H+ + 3e–)
1
(c)
(i)
At least one H2NCH2CH2NH2 with correct structure and bonding
to Cr via N
1
6 co–ordination with 3 en drawn correctly
1
Correct 3+ charge
(Mark independently but must not have 6 monodentate ligands)
1
Page 25 of 44
(ii)
Same (or similar) type of bonds broken and made
1
Same number of bonds broken and made
(or same co–ordination number)
1
(iii)
Entropy change (or ΔS) is positive (or increase in disorder)
1
Because there are more product particles than reactant particles
1
(d)
[Cr(H2O)6]2+
1
Reducing agent
(mark independently)
1
(e)
(i)
Ethanal (or CH3CHO) (not CH3COH)
1
(ii)
Ethanoic acid (or correct formula)
1
[18]
M2.
(a)
Same phase/state
1
(b)
Because only exist in one oxidation state
Allow do not have variable oxidation states
1
(c)
2I– + S2O82– → I2 + 2SO42–
Ignore state symbols
Allow multiples
1
(d)
Both (ions)have a negative charge
Or both have the same charge
Or (ions) repel each other
Do not allow both molecules have the same charge (contradiction)
1
Page 26 of 44
(e)
2Fe2+ + S2O82– → 2Fe3+ + 2SO42–
1
2Fe3+ + 2I– → 2Fe2+ + I2
1
Equations can be in any order
Positive and negative (ions)/oppositely charged (ions)
Mark independently
1
(f)
Equations 1 and 2 can occur in any order
Allow idea of Fe3+ converted to Fe2+ then Fe2+ converted back to
Fe3+
1
[8]
M3.
(a)
(Initially slow) because reaction is between two negative ions
(or between two negative reactants or two negative species)
1
Which repel each other
1
Then Mn2+ (or Mn3+) (ions) are formed acting as an autocatalyst
(QOL mark)
(or answer such as Mn2+ ions formed in the reaction act as a catalyst)
1
2MnO4– + 16H+ + 5C2O42– → 2Mn2+ + 8H2O + 4CO2
1
MnO4– + 4Mn2+ + 8H+ → 5Mn3+ + 4H2O
1
C2O42– + 2Mn3+ → 2Mn2+ + 2CO2
1
(Note these equations may gain credit if they have spectator ions
and/or be written as half equations)
Page 27 of 44
(b)
Active sites are where reactants are adsorbed onto a catalyst surface
(or bind or react on a catalyst surface)
(do not allow absorbed)
1
(Number of active sites increases if) surface area is increased
(or catalyst spread thinly)
(or on honeycomb)
(or powdered)
(or decreased particle size)
1
Active sites blocked by another species (or poison)
(or species adsorbed more strongly)
(or species adsorbed irreversibly)
(or species not desorbed)
(Note, credit any answer that implies blocked but not just active
site ‘poisoned’)
1
Sulphur (compounds) in Haber process
(or lead in a catalytic converter)
(Note do not allow enzymes unless immobilised)
1
[10]
M4.
(a)
Incomplete (or partially filled) d orbitals/sub-shells
Do not allow d shell
1
(b)
Variable oxidation states
1
(c)
(i)
[H3N–Ag–NH3]+
Allow [Cl–Ag–Cl]– or similar Cu(I) ion
Allow compounds in (i), (ii) and (iii) (eg Cl-Be-Cl)
Allow no charge shown, penalise wrong charge(s)
1
(ii)
Cis platin drawn out as square planar
Allow NiX42– etc
1
(iii)
[CuCl4]2– drawn out as tetrahedral ion
Or [CoCl4]2– drawn out
1
Page 28 of 44
(d)
(i)
SO2 + 1/2O2 → SO3
Allow multiples
Allow SO2 + 1/2O2 + H2O → H2SO4
ignore state symbols
1
(ii)
In a different phase/state (from the reactants)
1
(iii)
V2O5 + SO2 → V2O4 + SO3
can be in either order
1
V2O4 + 1/2O2 → V2O5
allow multiples
1
(iv)
Surface area is increased
1
By use of powder or granules or finely divided
Allow suspending/spreading out onto a mesh or support
1
(e)
(i)
Forms two or more co-ordinate bonds
Allow more than one co-ordinate bond or donates more than 1
electron pair.
Do not allow “has more than one electron pair”
Allow uses more than one atom to bond (to TM)
1
(ii)
Number of product particles > Number of reactant particles
Allow molecules/entities instead of particles
Penalise incorrect numbers (should be 2→5)
1
Disorder increases or entropy increases
(or entropy change is positive)
Allow ΔG must be negative because ΔH = 0 and ΔS is +ve
1
(iii)
6
1
Cyanide strongly bound to Co (by co-ordinate/covalent bond)
1
[16]
Page 29 of 44
M5.
(a)
2Fe2+ + S2O82– →2Fe3+ +2SO42–
1
2Fe3+ + 2I– → 2Fe2+ + I2
1
two negative ions repel / lead to reaction that is slow / lead
to reaction that has high Ea
1
iron able to act because changes its oxidation state
allow iron has variable oxidation state
1
With iron ions have alternative route / route with lower
activation energy
1
(b)
(i)
[Fe(H2O)6]3+ → [Fe(H2O)5OH]2+ + H+
can have H2O on LHS and H3O+ on R
do not penalise further hydrolysis equations
allow high charge density
1
Fe3+ ion has higher charge (to size ratio) (than Fe2+)
1
increases polarisation of co-ordinated water / attracts O
releasing an H+ ion / weakens O–H bond
1
(ii)
Cr2O72– + 14H+ + 6Fe2+ → 2Cr3+ + 7H2O + 6Fe3+
or 6 mol Fe(II) react with 1 mol dichromate
If factor of 6 not used max = 3 for M2, M4 and M5
e.g. 1:1 gives ans= 8.93 to 8.98% (scores 3)
1
moles dichromate = 23.6 × 0.218/1000 = 5.14 × 10–4
1
moles iron = 5.14 × 10–4 × 6 = 0.00309
M3 also scores M1
1
mass iron = 0.00309 × 55.8 = 0.172
Mark is for moles of iron × 55.8 conseq
Allow use of 56 for iron
1
% by mass of iron = 0.172 × 100/0.321 = 53.7%
Answer must be to at least 3 sig figures allow 53.6 to 53.9
Mark is for mass of iron × 100/0.321 conseq
1
Page 30 of 44
(c)
brown precipitate / solid
Allow red-brown / orange solid
Not red or yellow solid
1
bubbles (of gas) / effervescence/ fizz
Allow gas evolved / given off
Do not allow just gas or CO2 or CO2 gas
1
2[Fe(H2O)6]3+ + 3CO32– → 2Fe(H2O)3(OH)3 + 3CO2 + 3H2O
Allow
2[Fe(H2O)6]3+ + 3CO32– → 2Fe(OH)3 + 3CO2 + 9H2O
Use of Na2CO3
e.g. … + 3Na2CO3 → .. + .. + .. + 6Na+
1
[16]
M6.
(a)
(i)
absorbs (certain frequencies of) (white) light / photons
not absorbs white / u.v. light
1
d electrons excited / promoted
or d electrons move between levels / orbitals
d electrons can be implied elsewhere in answer
1
the colour observed is the light not absorbed / light
reflected / light transmitted
allow blue light transmitted
penalise emission of light in M3
1
Page 31 of 44
(ii)
ΔE is the energy gained by the (excited) electrons (of Cu2+)
allow:
• energy difference between orbitals / sub-shells
• energy of photon / light absorbed
• change in energy of the electrons energy lost by
excited electrons
• energy of photon / light emitted
1
h (Planck's) constant
1
v frequency of light (absorbed by Cu2+(aq))
do not allow wavelength
If energy lost / photon lost / light emitted in M1 do not penalised
light emitted
1
(iii)
[Cu(H2O)6]2+ + 4Cl– → [CuCl4]2– + 6H2O
note that [CuCl4–]2– is incorrect
penalise charges shown separately on the ligand and overall
penalise HCl
1
tetrahedral
1
Cl– / Cl / chlorine too big (to fit more than 4 round Cu)
allow
water smaller than Cl–
explanation that change in shape is due to change in
co-ordination number
1
(b)
allow:
• ion drawn with any bond angles
• ion in square brackets with overall / 2- charge shown
outside the brackets
• ion with delocalised O=C–O bonds in carboxylate
group(s)
1
lone pair(s) on O– / O
allow position of lone pair(s) shown on O in the diagram even if the
diagram is incorrect.
1
Page 32 of 44
(c)
(i)
[Cu(H2O)6]2+ + 2C2O42– → [Cu(C2O4)2(H2O)2]2– + 4H2O
product correct
1
equation balanced
1
6
note can only score M3 and M4 if M1 awarded or if complex in
equation has 2 waters and 2 ethanedioates
1
octahedral
If this condition is satisfied the complex can have the
wrong charge(s) to allow access to M3 and M4 but not M1
1
(ii)
ignore charges
diagram must show both ethanedioates with correct bonding
ignore water
1
90°
allow 180°
mark bond angle independently but penalise if angle incorrectly
labelled / indicated on diagram
1
[17]
M7.
(a)
1s2 2s2 2p6 3s2 3p6 3d10
allow [He] 2s2 . or [Ne] 3s2.or [Ar]3d10
1
d sub-shell / shell / orbitals / sub-level full (or not partially full)
can only score M2 if d10 in M1 correct
allow ‘full d orbital’ if d10 in M1
do not allow d block
1
Page 33 of 44
(b)
atom or ion or transition metal bonded to / surrounded by
one or more ligands
Allow Lewis base instead of ligand
1
by co–ordinate / dative (covalent) bonds / donation of
an electron pair
can only score M2 if M1 correct
1
(c)
H2 / hydrogen
do not allow H
1
no lone / spare / non-bonded pair of electrons
only score M2 if M1 correct or give ‘H’ in M1
1
(d)
(i)
+2 or 2+ or Pd2+ or II or +II or II+ or two or two plus
1
(ii)
tetrahedral
these shapes can be in any order
1
square planar
allow phonetic spelling e.g. tetrahydral
1
[9]
M8.
(a)
Variable oxidation state
1
eg Fe(II) and Fe (III)
Any correctly identified pair
Allow two formulae showing complexes with different oxidation
states even if oxidation state not given
1
(Characteristic) colour (of complexes)
1
eg Cu2+(aq) / [Cu(H2O)6]2+ is blue
Any correct ion with colour scores M3 and M4
Must show (aq) or ligands OR identified coloured compound
e.g. CoCO3)
1
(b)
Tetrahedral
1
Page 34 of 44
[CuCl4]2– / [CoCl4]2–
Any correct complex
(Note charges must be correct)
1
Square planar
1
(NH3)2PtCl2
Any correct complex
1
Linear
Do not allow linear planar
1
[Ag(NH3)2]+
[AgCl2]– etc
1
(c)
(i)
[Ca(H2O)6]2+ + EDTA4–
[CaEDTA]2– + 6H2O
If equation does not show increase in number of moles of particles
CE = 0/3 for (c)(ii)
If no equation, mark on
1
(ii)
2 mol of reactants form 7 mol of products
Allow more moles/species of products
Allow consequential to (c)(i)
1
Therefore disorder increases
1
Entropy increases / +ve entropy change / free-energy change is negative
1
(iii)
Moles EDTA = 6.25 × 0.0532 / 1000 = (3.325 × 10–4)
1
Moles of Ca2+ in 1 dm3 = 3.325 × 10–4 × 1000 / 150 = (2.217 × 10–3)
Mark is for M1 × 1000 / 150 OR M1 × 74.1
If ratio of Ca2+ : EDTA is wrong or 1000 / 150 is wrong, CE and can
score M1 only
This applies to the alternative
1
Page 35 of 44
Mass of Ca(OH)2 = 2.217 × 10–3 × 74.1 = 0.164 g
M1 × 74.1 × 1000 / 150
Answer expressed to 3 sig figs or better
Must give unit to score mark
Allow 0.164 to 0.165
1
[17]
M9.
(a)
2MnO4– + 16H+ + 5C2O42–
2Mn2+ + 8H2O + 10CO2
For all species correct / moles and species correct but charge
incorrect
1
For balanced equation including all charges (also scores first
mark)
1
(b)
Manganate(VII) ions are coloured (purple)
1
All other reactants and products are not coloured (or too faintly coloured to detect)
Allow (all) other species are colourless
Allow Mn2+ are colourless / becomes colourless / pale pink
1
(c)
The catalyst for the reaction is a reaction product
1
Reaction starts off slowly / gradient shallow
1
Then gets faster/rate increases / gradient increases
Allow concentration of MnO4– decreases faster / falls rapidly
1
(d)
Mn2+ ions
Allow Mn3+ ions
1
(e)
MnO4– + 8H+ + 4Mn2+
5Mn3+ + 4H2O
Allow multiples
1
2Mn3+ + C2O42–
2Mn2+ + 2CO2
1
[10]
Page 36 of 44
M10.
(a)
For reactions 1 to 3 must show complex ions as reactants and products
Take care to look for possible identification on flow chart
Reaction 1
ammonia solution
1
W is [Co(NH3)6]2+
1
[Co(H2O)6]2+ + 6NH3 → [Co(NH3)6]2+ + 6H2O
Correct equation scores all 3 marks
1
Reaction 2
Allow oxygen, Do not allow air
H2O2
1
X is [Co(NH3)6]3+
1
2[Co(NH3)6]2+ + H2O2 → 2[Co(NH3)6]3+ + 2OH–
Allow 2[Co(NH3)6]2+ + ½O2 + H2O → 2[Co(NH3)6]3+ + 2OH–
Correct equations score all 3 marks
1
Reaction 3
HCl
Do not allow Cl– but mark on
1
Y is [CoCl4]21
[Co(H2O)6]2+ + 4Cl– → [CoCl4]2- + 6H2O/
Correct equation scores previous mark
[Co(H2O)6]2+ + 4HCl → [CoCl4]2- + 6H2O + 4H+
This equation scores all three marks
1
Reaction 4
Na2CO3
Or NaOH/NH3
Do not allow CaCO3 as a reagent but mark on
1
Page 37 of 44
Z is CoCO3
Co(OH)2/Co(H2O)4(OH)2
1
[Co(H2O)6]2+ + CO32- → CoCO3 + 6H2O [Co(H2O)6]2++ 2OH–→ Co(H2O)4(OH)2+ 2H2O etc
Allow waters to stay co-ordinated to Co. This mark also previous
mark
Or [Co(H2O)6]2+ + Na2CO3 → CoCO3 + 6H2O + 2Na+
Allow Co2+ + CO32- → CoCO3
1
(b)
SO32- + ½O2 → SO42Allow multiples
1
The activation energy is lower (for the catalysed route)
Or Co3+ attracts SO32-/Co2+ attracts SO32-/oppositely charged ions
attract
1
½O2 + 2Co2+ + 2H+ → H2O + 2Co3+
1
2Co3+ + SO32- + H2O → 2Co2+ + SO42- + 2H+
Allow these equations in either order
1
[16]
M11.
(a)
Variable oxidation state
1
eg Fe(II) and Fe (III)
Any correctly identified pair
Allow two formulae showing complexes with different oxidation
states even if oxidation state not given
1
(Characteristic) colour (of complexes)
1
eg Cu2+(aq) / [Cu(H2O)6]2+ is blue
Any correct ion with colour scores M3 and M4
Must show (aq) or ligands OR identified coloured compound
e.g. CoCO3)
1
Page 38 of 44
(b)
Tetrahedral
1
[CuCl4]2– / [CoCl4]2–
Any correct complex
(Note charges must be correct)
1
Square planar
1
(NH3)2PtCl2
Any correct complex
1
Linear
Do not allow linear planar
1
[Ag(NH3)2]+
[AgCl2]– etc
1
(c)
(i)
[Ca(H2O)6]2+ + EDTA4–
[CaEDTA]2– + 6H2O
If equation does not show increase in number of moles of particles
CE = 0/3 for (c)(ii)
If no equation, mark on
1
(ii)
2 mol of reactants form 7 mol of products
Allow more moles/species of products
Allow consequential to (c)(i)
1
Therefore disorder increases
1
Entropy increases / +ve entropy change / free-energy change is negative
1
(iii)
Moles EDTA = 6.25 × 0.0532 / 1000 = (3.325 × 10–4)
1
Moles of Ca2+ in 1 dm3 = 3.325 × 10–4 × 1000 / 150 = (2.217 × 10–3)
Mark is for M1 × 1000 / 150 OR M1 × 74.1
If ratio of Ca2+ : EDTA is wrong or 1000 / 150 is wrong, CE and can
score M1 only
This applies to the alternative
1
Page 39 of 44
Mass of Ca(OH)2 = 2.217 × 10–3 × 74.1 = 0.164 g
M1 × 74.1 × 1000 / 150
Answer expressed to 3 sig figs or better
Must give unit to score mark
Allow 0.164 to 0.165
1
[17]
M12.
(a)
Co-ordinate / dative / dative covalent / dative co-ordinate
Do not allow covalent alone
1
(b)
(lone) pair of electrons on oxygen/O
If co-ordination to O2-, CE=0
1
forms co-ordinate bond with Fe / donates electron pair to Fe
‘Pair of electrons on O donated to Fe’ scores M1 and M2
1
(c)
180° / 180 / 90
Allow any angle between 85 and 95
Do not allow 120 or any other incorrect angle
Ignore units eg °C
1
(d)
(i)
3 : 5 / 5 FeC2O4 reacts with 3 MnO4–
Can be equation showing correct ratio
1
(ii)
M1 Moles of MnO4– per titration = 22.35 × 0.0193/1000 = 4.31 × 10–4
Method marks for each of the next steps (no arithmetic error allowed for M2):
Allow 4.3 × 10–4 ( 2 sig figs)
Allow other ratios as follows:
eg from given ratio of 7/3
1
M2 moles of FeC2O4= ratio from (d)(i) used correctly × 4.31 × 10–4
M2 = 7/3 × 4.31 × 10–4 = 1.006 × 10–3
1
M3 moles of FeC2O4 in 250 cm3 = M2 ans × 10
M3 = 1.006 × 10–3 × 10 = 1.006 × 10–2
1
Page 40 of 44
M4 Mass of FeC2O4.2H2O = M3 ans × 179.8
M4 = 1.006 × 10–2 × 179.8 = 1.81 g
1
M5 % of FeC2O4.2H2O = (M4 ans/1.381) × 100
M5 = 1.81 × 100/1.381 = 131 % (130 to 132)
1
(OR for M4 max moles of FeC2O4.2H2O = 1.381/179.8 (= 7.68 × 10–3)
for M5 % of FeC2O4.2H2O = (M3 ans/above M4ans) × 100)
eg using correct ratio 5/3:
Moles of FeC2O4 = 5/3 × 4.31 × 10–4 = 7.19 × 10–4
Moles of FeC2O4 in 250 cm3 = 7.19 × 10–4 × 10 = 7.19 × 10–3
Mass of FeC2O4.2H2O = 7.19 × 10–3 × 179.8 = 1.29 g
% of FeC2O4.2H2O = 1.29 × 100/1.381 = 93.4 (allow 92.4 to 94.4)
Note correct answer ( 92.4 to 94.4) scores 5 marks
Allow consequentially on candidate’s ratio
eg M2 = 5/2 × 4.31 × 10–4 = 1.078 × 10–3
M3 = 1.0078 × 10–3 × 10 = 1.078 × 10–2
M4 = 1.078 × 10–2 × 179.8 = 1.94 g
M5 = 1.94 × 100/1.381 = 140 % (139 to 141)
Other ratios give the following final % values
1:1 gives 56.1% (55.6 to 56.6)
5:1 gives 281% (278 to 284)
5:4 gives 70.2% (69.2 to 71.2)
[10]
M13.
(a)
For reactions 1 to 3 must show complex ions as reactants and products
Take care to look for possible identification on flow chart
Reaction 1
ammonia solution
1
W is [Co(NH3)6]2+
1
[Co(H2O)6]2+ + 6NH3 → [Co(NH3)6]2+ + 6H2O
Correct equation scores all 3 marks
1
Reaction 2
Allow oxygen, Do not allow air
H2O2
1
Page 41 of 44
X is [Co(NH3)6]3+
1
2[Co(NH3)6]2+ + H2O2 → 2[Co(NH3)6]3+ + 2OH–
Allow 2[Co(NH3)6]2+ + ½O2 + H2O → 2[Co(NH3)6]3+ + 2OH–
Correct equations score all 3 marks
1
Reaction 3
HCl
Do not allow Cl– but mark on
1
Y is [CoCl4]21
[Co(H2O)6]2+ + 4Cl– → [CoCl4]2- + 6H2O/
Correct equation scores previous mark
[Co(H2O)6]2+ + 4HCl → [CoCl4]2- + 6H2O + 4H+
This equation scores all three marks
1
Reaction 4
Na2CO3
Or NaOH/NH3
Do not allow CaCO3 as a reagent but mark on
1
Z is CoCO3
Co(OH)2/Co(H2O)4(OH)2
1
[Co(H2O)6]2+ + CO32- → CoCO3 + 6H2O [Co(H2O)6]2++ 2OH–→ Co(H2O)4(OH)2+ 2H2O etc
Allow waters to stay co-ordinated to Co. This mark also previous
mark
Or [Co(H2O)6]2+ + Na2CO3 → CoCO3 + 6H2O + 2Na+
Allow Co2+ + CO32- → CoCO3
1
(b)
SO32- + ½O2 → SO42Allow multiples
1
Page 42 of 44
The activation energy is lower (for the catalysed route)
Or Co3+ attracts SO32-/Co2+ attracts SO32-/oppositely charged ions
attract
1
½O2 + 2Co2+ + 2H+ → H2O + 2Co3+
1
2Co3+ + SO32- + H2O → 2Co2+ + SO42- + 2H+
Allow these equations in either order
1
[16]
Page 43 of 44
Page 44 of 44