Transition Metals Flashcards by Omer Eldaw

What is a transition metal?

Metals that contain an incomplete d sub shell in at least one of their ions

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Where are transition metals found?

In the ‘d block’ (middle, group 3)

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Why are Sc and Zn technically NOT transition metals, despite being found in the d block?

They have no or complete d shells
Sc 3+ = [Ar] Zn 2+ = [Ar] 3d10

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What is a ligand?

An atom or ion which donates a lone pair to form a co-ordinate bond to metal

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What is a complex?

A metal ion with ligands co-ordinately bonded to it

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What is the co-ordination number?

The number of co-ordinate bonds from ligands to the metal ion in the complex

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What is a bidentate ligand?

A ligand which forms two co-ordinate bonds. Two different lone pairs on the molecule donate two electron pairs

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Give 2 examples of a monodentate ligand

H2O: :OH- :NH3 :CN- :Cl

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When can optical isomerism occur in complex molecules?

Can occur when bidentate ligands are attached to an octahedral complex

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Give an example of a multidentate ligand

EDTA 4-, haem, [Pt(NH3)2Cl2] (cisplatin), [Ag(NH3)2]+

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Why is EDTA 4- such an effective ligand, and what is its structure?

It has 6 lone pairs, and so can form 6 co-ordinate bonds with a metal ion

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[Cu(H2O)6]2+ is added with an unknown substance. The solution turns from light blue to dark blue. What was the unknown substance?

Ammonia

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Ammonia is added to [Cu(H2O)6]2+. What are the products formed?

[Cu(NH3)4(H2O)2]2+ + 4H2O

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Concentrated HCl is added to [Cu(H2O)6]2+. What are the products formed?

[CuCl4]2- + 6H2O

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Ammonia is added to [Cu(H2O)6]2+. What is the colour change observed?

Light blue to dark blue

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Concentrated HCl is added to [Cu(H2O)6]2+. What is the colour change observed?

Light blue to yellow

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Concentrated HCl is added to [Cu(H2O)6]2+. The solution should turn yellow, but it looks more green. Why?

Because it’s going from blue to yellow

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Ammonia is added to [Co(H2O)6]2+. What are the products formed?

[Co(NH3)6]2+ + 6H2O

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Ammonia is added to [Co(H2O)6]2+. What is the colour change observed?

Pink to pale brown

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Concentrated HCl is added to [Co(H2O)6]2+. What is the colour change observed?

Pink to dark blue

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Concentrated HCl is added to [Co(H2O)6]2+. What are the products formed?

[CoCl4]2- + 6H2O

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Why is the colour change so dramatic when concentrated HCl is added to [Co(H2O)6]2+?

The colour change is dramatic because the co-ordination number also changes (Cl is big so can’t fit round octahedral)

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What is the chelate effect and why is it feasible (refer to delta G)?

The substitution of monodentate ligands (eg H2O) by multidentate ligands. This happens as entropy change is positive, /\H is roughly zero and therefore /\G is negative, meaning the reaction is feasible.

What is a use of a chelate?

It is useful in dealing with heavy metal poisoning, as it ‘cages’ up and so limits the poisoning effects

What is the equation to work out the energy change, using Plank's constant and lamda?

Energy = hv where h = Plank's constant and lamda = the speed of light/wavelength

What are the factors that affect the size of energy gap?

The metal, the oxidation state, the ligands, the co-ordination number

Why are some substances able to give different colours/observations?

They have a variable oxidation state

KMnO4 is titrated against acidified Fe2+. What colour change is observed?

Colourless to pink

KMnO4 is used in a redox titration against acidified Fe2+. After all the acid has been used up, the colour change observed is brown/dark red rather than pink. What has happened?

There was not enough acid to full oxidise the MnO4- Instead MnO2 formed

What colour is MnO4-?

Purple

A student is choosing an acid to acidify Fe2+ for a redox titration. The options are dilute H2SO4, conc H2SO4 and dilute HCl. Which acid should she choose? Give reasons why the others are unsuitable.

Should choose dilute H2SO4 Conc H2SO4 is an oxidising agent, but there is already an oxidising agent present Dilute HCl - Cl could be oxidised (Cl2 gas), so the titration would larger and thus inaccurate.

The complex ion formed in aqueous solution between cobalt (II) ions and chloride ions is a different colour from the [Co(H2O)6]2+ ion. Explain why these complexes have different colours

Ligands are different and so cause different d orbital splitting. This means different amounts of energy are required to promote electron to the next energy level and so different frequencies of light are absorbed. Therefore different wavelengths/colours of light are transmitted

Fill the blanks. Heterogenous catalysts reactions often involve a ____ catalyst and _____ reactants.

solid catalyst and gaseous reactants

Describe alternate pathway a heterogenous catalyst provides

Reactants adsorbed onto the surface (active sites) - weakens bonds - brings molecules closer - more favourable orientation Reaction occurs Products desorbed

What is the issue if a catalyst bonds too strongly to a reactant?

It will never let go - both the catalyst and reactant will be unable to take part in the reaction

What is the issue if a catalyst bonds too weakly to a reactant?

If it bonds too weakly, it will not have the desired affects.

What is the contact process and which catalyst does it involve?

A way of producing SO3 from SO2, and then producing sulfuric acid Involves a vanadium (V) oxide catalyst

Give two half equations to show the contact process

SO2 + V2O5 --> V2O4 + SO3 V2O4 + 1/2 O2 --> V2O5

What is catalyst poisoning?

When the catalyst is covered by a substance which blocks the active sites, thus making it ineffective

Fill in the blank. Homogenous catalysts are mostly involved in reactions in a _____ with a catalyst in a _______

Solution for both

What is an autocatalyst?

A catalyst that is also one of the products of the reaction being catalysed.

Give a half equation showing the reduction of manganate

MnO4- + 8H+ + 5e- --> Mn2+ + 4H2O

Give two half equations to show the reaction of iodide ions and S2O8 2- to form iodine and sulphate ions with Fe 2+ as the homogenous catalyst

S2O8 2- + 2Fe 2+ --> 2SO4 2- + 2Fe 3+ 2I- + 2Fe 3+ --> I2 + 2Fe 2+

Give 2 half equations to show the reaction of MnO4- with C2O4 2- which is an example of an autocatalysis reaction

1) 2MnO4- + 16H+ + 8Mn2+ --> 10Mn3+ + 8H2O 2) 5C2O4 2- + 10Mn3+ --> 10CO2 + 10Mn2+

Give the formula of cisplatin

[Pt(NH3)2Cl2]

How many lone pairs are there on EDTA 4-?

Give the formula of ethanedioate

C2O4 2-

Give the formula of 1,2-diaminoethane

AKA en H2N-CH2-CH2-NH2

What is a hint as to whether a complex ion is a square planar or tetrahedral?

Most complex ions are tetrahedral in shape, but complex ions containing Nickel, Palladium or Platinum tend to be square planar.

Give an example of a process involving a heterogeneous catalyst

Contact Process, which is where V2O5 acts as a heterogeneous catalyst to allow the reactants to adsorb onto it and react.

Give an example of a process involving a homogeneous catalyst

The reaction between iodide and peroxydisulfate. This is where Fe2+ acts a catalyst to allow the two negatively charged molecules to be able to react with each other.

How does carbon monoxide poisoning arise?

This comes from the haemoglobin forming a stable and permanent bond with CO, meaning its useless, as opposed to H2O, O2 and CO2, which will form unstable bonds with haemoglobin.

What is the chemical equation for the conversion of SO2 into SO3 and the regeneration of the catalyst vanadium(V) in the contact process?

1) SO2 (g) + V2O5 (s) -> SO3 (g) + V2O4 (s) oxdiation state of Vanadium - 5+ to 4+ 2) V2O4 (s) + 1/2O2 (g) -> V2O5 (s) oxidation state of Vanadium - 4+ to 5+

What is the chemical equation for the conversion of SO3 into H2SO4 in the contact process?

1) SO3 (g) + H2SO4 (l) -> H2S2O7 (s) 2) H2S2O7 (l) +H2O (l) -> 2H2SO4 (l)

State 3 ways in which a transition metal complex can be changed to alter its colour

1. change ligand 2. change oxidation state of transition metal 3. change coordination number