che-2c32: inorganic past exam...

CHE-2C32: Inorganic

Past Exam Papers

Sorted by Topic then Year

Transition Metal Catalysis – Dr. Wright

2006/7

Answer ALL parts (a), (b), (c) and (d).

(a) Compounds A to E are intermediates in a hydroformylation catalytic cycle. Assign

an electron count to each compound and determine which, if any, obey the 18-electron

rule. State the formal oxidation state of the cobalt in each compound.

[30%]

(b) Draw a catalytic cycle incorporating at least the five compounds A-E as

intermediates and indicate which additional substrate molecules would have to be

present to facilitate the conversions, where they would join the catalytic cycle, and at

what point the product would be released.

[30%]

(c) State the reaction type for each of the steps in the catalytic cycle.

[20%]

(d) RhH(CO)(PPh3)2 also catalyses alkene hydroformylation. What are the

advantages of rhodium phosphine catalysts over the cobalt carbonyl system?

[20%]

Answer BOTH parts (a) and (b).

(a) (i) Draw the mechanism for the polymerisation of ethene by the metallocene

catalyst [Cp2ZrR]+.

[20%]

(ii) Describe, with the aid of diagrams, two potential chain transfer pathways leading

to control of polymer molecular weight in homogeneous alkene polymerisation

catalysis.

[20%]

(iii) Provide two methods for the preparation of [Cp2ZrR]+ from the neutral precursor

Cp2ZrCl2.

[20%]

(b) Briefly discuss the factors which control the rates and stereochemistry of

substitution at square planar Pt(II) complexes.

[40%]

2007/8


(a) Compounds A to E are involved in a hydrogenation catalytic cycle. Assign an

electron count to each compound and determine which, if any, obey the 18-electron

rule. State the formal oxidation state of the rhodium in each compound.

[30%]

(b) Draw a catalytic cycle incorporating at least the five compounds A to E as

intermediates and indicate which additional substrate molecules would have to be

present to facilitate the conversions, where they would join the catalytic cycle, and at

what point the product would be released.

[30%]

(c) State the reaction type for each of the steps in the catalytic cycle you have drawn

in answer to part (b).

[20%]

(d) Discuss how Wilkinson’s catalyst can be modified for asymmetric hydrogenation.

[20%]


(a) (i) Discuss the active species involved in group IV metallocene-based olefin

polymerisation and how this has informed the design of new iron(II) catalysts.

[20%]

(ii) Discuss the role of methylaluminoxane (MAO) in olefin polymerisation.

[20%]

(iii) Provide two methods for the preparation of [(ArNCH2CH2NAr)NiCH3]+ from the

neutral precursor [(ArNCH2CH2NAr)NiCl2] (Ar = aryl substituent).

[20%]

2008/9

Answer ALL parts (a), (b), (c), and (d).

(a) Compounds A to D are involved in a hydrocyanation catalytic cycle. Assign an

electron count to each compound and determine which, if any, obey the 18-electron

rule. State the formal oxidation state of the nickel in each compound.

[Note: L = P(O-o-tolyl)3].

[20%]

(b) Draw a catalytic cycle for the hydrocyanation of ethylene incorporating at least the

four compounds A-D and indicate which additional substrate molecules would have to

be present to facilitate the conversions, where they would join the catalytic cycle, and

at what point the product would be released.

[30%]


[20%]

(d) Discuss the formation of the anti-Markovnikov product in the hydrocyanation of

butadiene.

[30%]

2008/9

Answer ALL parts (a), (b) and (c).

(a) Discuss the Shell Higher Olefin Process (SHOP) using Keim’s nickel catalyst.

[30%]

(b) Provide two examples of chromium-based constrained geometry catalysts. In each

case give the oxidation state of the chromium, and discuss the catalytic activity.

[30%]

2009/10


(a) For each of the following catalysts (i) to (iii), indicate the catalytic process

commonly associated with each catalyst. For the rhodium catalyzed process, give the

full catalytic cycle.

[40%]

(i) [HCo(CO)4]

(ii) [RhCl(PPh3)3]

(iii) [(η5-Me4C5SiMe2-η1-NtBu)CrR] (R = CH2SiMe3)

(b) Compare and contrast the structural features of the complexes A and B in terms of

their effectiveness as potential ethylene polymerization catalysts.

[30%]

(c) Discuss how Fe(II) procatalysts containing the bis(imino)pyridine ligand C can

be modified so that they can be covalently supported on silica.

[30%]


(a) Describe the synthesis of the complex E from sodium molybdate. Show how

changing the alkoxide ligands [OR] from tert-butoxide [OtBu] to hexafluoro-tert-

butoxide [OC(CF3)2CH3] affects the polymerization of the monomer F.

[30%]

(b) Outline the steps in the catalytic formation of propionitrile from ethene using a nickel

catalyst. In each stage of the catalytic cycle, indicate clearly the type of mechanistic

step taking place.

[30%]

2010/11


(a) For each of the following catalysts, indicate the catalytic process commonly

associated with each catalyst.

(i) [RhI2(CO)2]−

(ii) [Mo(NAr)(CHR)(OtBu)2] (R = CMe2Ph, Ar = 2,6-iPr2C6H3)

(iii) FeCl2[2,6-(ArN=CH)2C5H3N] (Ar = 2-MeC6H4)

(iv) Ni[P(O-otolyl)3]2

[20%]

(b) For the rhodium catalyzed process, give the full catalytic cycle.

[40%]

(c) Discuss the three proposals for the mode of operation of the Phillips catalyst. Which

is currently the preferred mechanism and why?

[40%]

(a) Discuss poly(ε-caprolactone) synthesis using a metal alkoxide catalyst. Illustrate

your answer with an example of a group IV metal system and indicate the percentage

conversion.

[30%]

2011/12

Answer ALL parts.

(a) For each of the following (pre-)catalysts, indicate the catalytic process commonly

associated with each catalyst.

(i) [2,6-(ArN=CH)2C5H3N]FeCl2 (Ar = 2-MeC6H4)

(ii) [HCo(CO)4]

(iii) [(ArN=CHCH=NAr)NiMe][MeB(C6F5)3] (Ar = 2,6-iPr2C6H3)

(iv) [La(2,4,6-tri-tert-butylphenolate)3]

[20%]

(b) For the cobalt catalysed process, give the full catalytic cycle, indicating the steps

involved and the formal oxidation state and electron count of the cobalt species

involved.

[60%]

(c) For Wilkinson’s catalyst [RhCl(PPh3)3], discuss how the catalyst can be modified

for asymmetric hydrogenation and give a substrate to illustrate your answer.

[20%]

Discuss the nickel catalysed hydrocyanation of a C=C double bond. Illustrate your

answer with a catalytic cycle, and indicate the nature of the complexes involved, giving

the oxidation state of the metal and electron count for the complex in each case.

[40%]

2012/13

Answer ALL parts (a) to (c).

(a) Name a catalytic process commonly associated with each of the following

(pre)catalysts:

(i) RuCl2(PPh3)2

(ii) HRh(CO)(PPh3)2

(iii) RuCl2(PCy3)2(=CHPh)

(iv) Cp2ZrCl2

[20%]

(b) Give a full catalytic cycle for a reaction that uses RuCl2(PCy3)2(=CHPh). Your

answer should include the electron count for each species of your chosen cycle.

[50%]

(c) Catalyst (iii) may be modified to enhance the stability of the catalyst and/or the

reaction rate. What modifications will achieve these enhancements and why?

Give examples of modified catalysts that offer enhanced performance.

[30%]

2013/14

Answer ALL parts (a) to (e).

(a) Compounds A to C are intermediates in a hydroformylation catalytic cycle. Assign

an electron count to each compound and determine which, if any, obey the 18-electron

rule. State the formal oxidation state of the rhodium in each compound.

[10%]

(b) Draw a catalytic cycle for rhodium-catalysed hydroformylation using

RhH(CO)(PPh3)3 as the pro-catalyst. Use compounds A–C as intermediates, adding

any others required, and indicate which additional substrate molecules would have to

be present to facilitate the conversions, where they would join the catalytic cycle, and

at what point the product would be released.

[30%]


[20%]

(d) Cobalt complexes also catalyse hydroformylation. What are the advantages of

the rhodium catalyst?

[20%]

(e) The commercial synthesis of Naproxen makes use of an asymmetric

hydroformylation before oxidation to yield the final product. Predict structures for the

starting material and product in the hydroformylation step. The reaction is catalysed

by [Rh(OAc2)2]2 plus a chiral ligand: suggest a general class of chiral ligand which

might be applicable here, and give at least one specific example.

[20%]

(a) (i) What are the key design features required in a pro-catalyst in order to obtain

high molar mass polyalkene products in a polymerisation reaction? Illustrate your

answer using a catalyst system derived from Cp2ZrCl2.

[30%]

(ii) How do activators such as triyl salts (e.g. [CPh3][B(C6F5)4]) contribute to high molar

masses in polyalkene polymerisation?

[20%]

Inorganic Chemistry Mechanism – Prof. Pickett

2006/7

Schemes 1 and 2 show the results of two 13C labelling studies carried out on the

reaction between methyl manganese pentacarbonyl and carbon monoxide in an inert

solvent. In Scheme 2 the product ratio F : G : H was found to be 2 : 1 : 1.

How would you interpret the information from these two studies, in terms of the

mechanism of the process? [50%]

2006/7

The hydroxide substitution reaction shown below has 2nd order kinetics such that the

rate law can be written as

-d[A]/dt = k[A][HO-]

In contrast, the rate of substitution of an octahedral complex is most usually insensitive

to the nature of the entering group and therefore shows 1st order kinetics.

In addition, the rate of the reaction remains unchanged when the reaction is carried

out in the presence of an excess of an anion such as SCN- and about 25% of the

product is the SCN- substituted species. Suggest a mechanism which could account

for these observations.

[40%]

(i) In general, the rate of substitution of an octahedral complex is insensitive to the

nature of the entering group. Discuss this in terms of D or Id pathways.

[20%]

(ii) A cis ligand can influence the rate of substitution of an octahedral complex by

stabilising the five coordinate transition state. Show how this electronic cis-effect can

arise.

[20%]

2008/9

(c) Discuss the stereochemistry of substitution reactions at square planar complexes.

[40%]

Discuss how Transition State Stabilisation and Ground State Destabilisation can

provide an explanation of the ordering of ligands in the shortened Trans Effect series

for square planar complexes:

CO, C2H4 > PR3, H > Me > Br,Cl > NH3, H2O

[40%]


(a) Discuss the mechanism of insertion of carbon monoxide into the Mn(I) methyl

compound F with particular reference to:

(i) evidence for the origin of the acyl carbonyl in the product G

(ii) which of the ligands are involved in migration.

[40%]

(b) Potassium iron(III) hexacyanoferrate(II), KFeIII[FeII(CN)6], gives rise to an electronic

absorption band at 714 nm. The complex ion [Tc2Cl8]3− shows an absorption at 1695

nm.

Explain and contrast the origins of these two bands.

[60%]

2009/10

(c) Discuss the mechanistic aspects of the type of electron - transfer process typified

by the system:

[*FeII(OH2)6]2+ + [FeIII(OH2)6]3+ <-> [*FeIII(OH2)6]3+ + [FeII(OH2)6]2+

[40%]

2010/11

(i) What do you understand by an A or Ia substitution mechanism for square-planar

Pt(II) complexes ?

(ii) What is the principal stereochemical feature of ligand substitution at Pt(II) and how

does this arise?

(iii) How does a bulky ligand in the cis - position to the substituted ligand influence the

rate of substitution of a Pt(II) complex?

(iv) What is the trans effect and how does it operate?

(v) The rate law for the reaction of a Pt(II) complex to give a single substituted product

has the general form:

Rate = (kS[S] + kY[Y])[Pt(II)] where S is the solvent and Y the incoming ligand.

Define the rate constants kS and kY and discuss how this rate law is mechanistically

interpreted.

[70%]

The Scheme below shows a set of reactions for a molybdenum bis(dinitrogen)

complex carried out in an inert solvent (toluene) in the dark at 293 K .

Kinetic measurements show:

That each of the reactions (substitution, oxidation or alkylation of a dinitrogen ligand)

shows a first order dependence on the concentration of the complex, that each

reaction proceeds at a rate which is independent of the substrate concentration

(MeCN, MeBr or PhCH2Br), and that the apparent first order rate constant for each of

the reactions is the same.

Discuss these results and suggest mechanisms which might explain reactions (i), (ii),

and (iii). How might these mechanisms be further tested?

[60%]

2011/12

The Scheme shows a set of reactions for a molybdenum bis(dinitrogen) complex

carried out in an inert solvent (toluene) in the dark at 293 K. Kinetic measurements

show that each of the reactions (substitution, oxidation or alkylation of a dinitrogen

ligand) shows a first order dependence on the concentration of the complex, that is

independent of the substrate concentration (MeCN, MeBr or PhCH2Br). Moreover,

each reaction proceeds at the same rate.

Discuss these results, and suggest mechanisms that explain reactions (i,ii and iii) and

how these might be tested.

[60%]

The substitution of the coordinatively saturated closed-shell complex A to give the

product B might reasonably be expected to proceed via a dissociative mechanism.

However, the rate of the reaction is found to depend on the concentration of the

nucleophile PMe3. How can this first-order dependence on [PMe3] be explained?

[30%]

2012/13

Answer BOTH parts.

(a) (i) Square planar Pt(II) complexes usually undergo substitution by an associative,

A, or intimate associative, Ia, mechanism. Discuss this observation.

(ii) What is the principal stereochemical feature of ligand substitution at Pt(II) and

how does this arise?

(iii) How does a bulky ligand, placed in the cis-position relative to the substituted

ligand, influence the rate of substitution of a Pt(II) complex?

[45%]

(b) (i) What is the trans-effect and how does it operate?

(ii) The rate law for the reaction of a Pt(II) complex to give a single substituted product

has the general form:

Rate = (kS[S] + kY[Y])[Pt(II)]

where S is the solvent and Y the incoming ligand. Discuss how this is interpreted

mechanistically.

[55%]

Discuss the mechanistic aspects of the electron-transfer system:

[*FeII(OH2)6]2+ + [FeIII(OH2)6]3+ ⇌ [*FeIII(OH2)6]3+ + [FeII(OH2)6]2+

[60%]

2013/14

Answer ALL parts (a) to (d).

The figure shows data for the dependence of the observed rate constant kobs, for the

substitution of NHEt2 by NHMe2 in a square planar Pt(II) complex, on the concentration

of NHMe2. The data was obtained, at 25 °C, in two different solvents, methanol and

hexane.

(a) What is the order of the reaction with respect to NHMe2 in methanol and in hexane

respectively?

[10%]

(b) Explain why the kinetics of substitution are different in the two solvents?

[45%]

(c) Show, with the aid of a diagram, the two pathways for substitution. Explain how

these both lead to conservation of the trans stereochemistry in the product.

[30%]

(d) How might you expect the substitution kinetics to alter if NHMe2 were changed to

ditertiary butylamine, NHBut2 ?

[15%]

Metallic Interactions – Dr. Cheesman

2006/7

Answer ALL parts (a), (b), (c), (d) and (e).

(a) Draw d-orbital splitting diagrams for octahedral, tetrahedral and square planar

ligand geometries. Indicate the relative magnitudes of the orbital splittings for the

octahedral and tetrahedral cases.

[10%]

(b) What is the spectrochemical series?

[10%]

(c) Explain why the neutral molecule carbon monoxide is a strong-field ligand in the

spectrochemical series yet fluoride is a weak-field ligand.

[30%]

(d) A solution of [Mn(H2O)6]2+ has a faint pink colour while a solution of [MnBr4]2- is a

more intense green. Draw crystal field splitting diagrams for the two complexes,

account for their colours and explain why the intensities of the colours are very

different.

[20%]

(e) (i) What is the Jahn-Teller theorem?

[10%]

(ii) The electronic absorption spectrum of the [Ti(H2O)6]3+ ion, below, shows a broad

ligand field band centred at ~19000 cm-1. Explain how the Jahn-Teller theorem

accounts for the structure (indicated by arrows) observed on this band.

[20%]


(a) (i) What are ferromagnetic and antiferromagnetic coupling?

[15%]

(ii) What factors determine which of these two types of coupling will occur between the

spins of two transition metal ions in a complex?

[20%]

(iii) The structure of a fragment of the neutral linear polymeric complex of Cu2+ and

Mn2+, [Mn(II)Cu(II)(pba)(H2O)3]n, is shown below:

Describe the magnetic properties of this material and explain how they arise.

[15%]

2007/8


(a) For each of the following pairs of complexes, which has the larger value of ∆oct

and why?

(i) [CrF6]3- and [Cr(NH3)6]3+

(ii) [Cr(H2O)6]2+ and [Cr(H2O)6]3+

(iii) [MnF6]2- and [ReF6]2-

[15%]

(b) Derive an expression, in terms of ∆oct or ∆tet, for the crystal field stabilisation

energy (CFSE) of the following complexes:

(i) [TiF6]2- (ii) [Mn(H2O)6]3+ (iii) [NiCl4]2-

[15%]

(c) Using appropriate energy level diagrams, explain why CO is a stronger field

ligand than PR3.

[35%]

(d) The effective magnetic moments, µeff, for the transition metal complexes K3FeF6

and K3Mn(CN)6 are 5.90 µ B and 3.18 µ B respectively.

Using the formula µeff = √(n(n+2)) and these data as examples, explain what is

meant by the phrase “quenched orbital angular momentum”.

[35%]


(a) The figure below shows the structure of a complex of Fe(III).

(i) This complex can be found bound to proteins where it is often referred to as an iron-

sulfur cluster. Is this description correct? Explain how you came to this conclusion.

[10%]

(ii) Predict the spin state of each individual Fe(III) ion. Give reasons for your answer.

[20%]

(iii) The complex is found to be diamagnetic. Describe the nature of the interaction

between the two metal ions which leads to this property.

[20%]

(iv) What is the result of reducing the complex by one electron? Suggest one

measurement which could support your answer.

[10%]

2008/9


(a) (i) What are Hund’s rules?

(ii) What is the ground term for the free ion V3+? Show clearly how you obtained

your answer.

[20%]

(b) The figures below show the electronic absorption spectrum of the [V(H2O)6]3+ ion

in the UV-visible region and an Orgel diagram for the d2 configuration.

Using the assumptions that (i) ∆ is greater than 10 000 cm-1 and (ii) there are no bands

to lower energy, assign the bands in the absorption spectrum of the [V(H2O)6]3+ ion.

Give reasons for your assignment.

[40%]

(c) (i) Explain the significance of the formula µSO = 2√(S(S+1)).

(ii) The ions [V(H2O)6]3+ and [VCl4]- both give rise to a magnetic moment of µ = 2.8

µB. Explain these observations.

[40%]

2009/10


(a) (i) What is the ground term for the free ion Fe3+?

(ii) Sketch the shapes and orientations of the five d-orbitals.

(iii) Use your figure to explain the pattern of splitting in the energies of the d-orbitals

that results from an octahedral ligand field.

(iv) Explain quenching of orbital angular momentum by a ligand field. In your

answer, discuss the formula µ = 2√(S(S + 1)).

(v) The effective magnetic moment of the complex ion [FeF6]3− is µ eff = 5.90 µ B.

Explain this value.

(vi) Would you expect the magnetic moment of the free Fe3+ ion to differ from this

value?

[50%]

(b) The cation D shown below results from the reaction of [CrIII(oxalate)3]3− and

[NiII(Me6[14]ane-N4)]2+. For clarity, the full structures of the Me6[14]aneN4 ligands are

not shown.

(i) What are the spin-states of the individual chromium and nickel ions in this

compound? Explain how you arrive at your answer.

(ii) Explain how this structure leads to the molecule having an unusually high spin-

state.

[50%]

2010/11


(a) A solution of [Mn(H2O)6]2+ has an extremely faint pink colour whereas a solution of

[MnBr4]2− displays a more intense green colour.

(i) Draw ligand field splitting diagrams for the two complexes.

(ii) Give an explanation for the colours of these complexes.

(iii) Why is there a significant difference in the intensities of the colours of the

complexes?

[40%]

(b) The element technetium, Tc, forms a chloride with empirical formula K1.5TcCl4 that

is an example of a metal-metal bonded dinuclear complex.

(i) Describe the structure of this complex.

(ii) Suggest an appropriate d-orbital energy level scheme to account for the structure

of the complex and the nature of the metal-metal bonding.

[60%]


(a) This part concerns electronic states of transition metal ions.

(i) What are Hund’s rules?

(ii) What is the ground term for a free Cr3+ ion?

[20%]

(b) The electronic absorption spectrum of the [Ti(H2O)6]3+ ion, below, shows a broad

ligand field band centred at ~19000 cm−1.

(i) What is the Jahn-Teller theorem?

(ii) Explain how the Jahn-Teller theorem accounts for the structure observed for the

ligand field transition of [Ti(H2O)6]3+.

[20%]

2011/12

Answer ALL parts.

(a) What is the ground spectroscopic term for the free ion Co3+?

[15%]

(b) For each of the following pairs of complexes, which has the larger value of ∆oct

and why?

(i) [CoF6]3− and [Co(NH3)6]3+

(ii) [Co(H2O)6]2+ and [Co(H2O)6]3+

(iii) [Co(NH3)6]3+ and [Rh(NH3)6]3+

[24%]

(c) The stretching wavenumber of gaseous NO is νNO = 1876 cm−1. But for the

nitroprusside ion, [Fe(CN)5NO]2−, νNO is observed at 1935 cm−1.

(i) Draw a molecular orbital energy level diagram for the nitric oxide molecule and

from this derive the order of the N-O bond.

[26%]

(ii) By referring to your diagram, give an explanation for the value of νNO observed for

the nitroprusside ion.

[20%]

(iii) On the basis of these data, what would you predict the M-N-O angle to be in the

nitroprusside ion? Give your reasoning.

[15%]

Answer ALL parts.

(a) The compounds [Cr3O(OOCC6H5)6(pyridine)3]ClO4 and Cs3[Re3Cl12] both contain

trinuclear complex metal ions.

(i) Draw structures for the two complex ions.

[20%]

(ii) Are these structures cages or clusters? Explain your answer.

[10%]

(iii) What are the spins of the metal ions in the chromium complex and how are they

magnetically coupled? Specify the mechanism by which the spins interact. What is

the overall resultant ground state spin of the molecule?

[30%]

(iv) What is the electron count of each metal in the trinuclear rhenium complex?

[10%]

2012/13


(a) What is the ground term for the free ion Ni2+? Show how you arrive at your

answer.

[20%]

(b) What is the spin state of a Ni2+ ion coordinated by six identical ligands?

Show how you obtain your answer and explain why the exact nature of the ligand is

not important.

[20%]

(c) The figures below show, respectively, a Tanabe-Sugano diagram for the d8

electronic configuration, and the electronic absorption spectrum of the [Ni(H2O)6]2+

ion.

Using the Tanabe-Sugano diagram, assign the three bands observed in the spectrum.

Explain the reasoning behind your method and state any assumptions that you make.

[40%]

[You may annotate the copy of the Tanabe-Sugano diagram provided at the end of

this examination paper and attach this to your answer booklet].

(d) How do the intensities of these bands relate to the nature of the transitions

involved?

[20%]

(a) The figure below shows how electronic conductivity typically varies with

temperature for metals, semiconductors and insulators.

Explain how the concept of band structure can account for these differences in

behaviour. Include in your answer a description of the Fermi level.

[40%]

2013/14


(a) The effective magnetic moment, µ, of a free transition metal ion can be

calculated from the Van Vleck equation:

µ = √[𝐿(𝐿 + 1) + 4𝑆(𝑆 + 1)] µB

Define, and describe the origin of, the physical properties L and S.

[20%]

(b) Derive the ground term symbol for the free Cr2+ ion and calculate its effective

magnetic moment. Show how you arrive at your answer.

[20%]

(c) Under what circumstances is the Van Vleck equation simplified to the form

µ = 2√𝑆(𝑆 + 1)] µB ?

[15%]

Using this simplified formula, predict the effective magnetic moment of each of the

following species:

(i) [Cr(H2O)]3+ (ii) Ba2CrO4 (iii) K3Mn(CN)6

In each case, state whether or not you would expect the experimentally measured

value to differ from the prediction and explain your reasoning.

[30%]

(d) Give a brief explanation for why chromium(II) acetate (empirical formula

Cr(CH3CO2)2(H2O)) is diamagnetic.

[15%]

(i) By considering the coupling of two spins, SA = 5/2 and SB = 3/2, explain the

difference between ferromagnetic and antiferromagnetic coupling?

[15%]

(ii) What factors determine which of these two types of coupling will occur between

the spins of two transition metal ions in a complex?

[20%]

(iii) The structure of a fragment of the linear polymeric substance

[Mn(II)Cu(II)(pba)(H2O)3]n is shown below.

Describe the magnetic properties of the lowest energy magnetic state of this material

and explain how they arise.

[15%]

che-2c32: inorganic past exam...

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