2.4 - Transition Metals

Give 2 properties of Transition Metals

1. Transition metals occupy the d-block

2. Catalytic

Give 2 examples of Transition metals acting as a Catalyst

1. Platinum in fuel cell

2. Nickel in nitrile reduction to amines

What are the colours of CuSO₄ in different states? (when light shines on it)

• Why

• Solid = White

• Liquid = Cyan

Red light is absorbed so the complimentary colours show

How do we see a compound’s colour when light is cast on it?

Lights different wavelength of light shows the corresponding colours which have the exact amount of energy to excite electrons to the next orbital (given it has space for it)

What is the usual order of Subshells for Transition Metals?

• 2 anomalies + configuration (why)

3d 4s:

• Cr = [Ar] 4s¹3d⁵ → 3d is half filled to similar energy level to 4s, so the electron occupies it

• Cu = [Ar] 4s¹3d¹⁰

What does this effect in terms of ionisation?

When being ionised for Cu + Cr, the 4s s lost first or gains the electron

Why do Transition metals form coloured compounds?

• Range of metals

Transition metals are the only ions that are stable, whilst having partially filled d-orbitals → excitation of electrons to the partially filled orbitals and their de-excitation gives colour:

• Ti → Cu

Complex Ions

Complex Ions

What is a Ligand? (3 examples)

A particle with a lone pair that datively covalently bonds to a transition metal ion:

• H₂Ö

• N̈H₃

• :Cl^-

Why do Complex Ions with the same Metal have different co-ordinate numbers?

Ligands, for example Cl, are greater in size than other ligands, like NH₃, can only occupy space as a tetrahedral

What is the priority for a Complex Ions when writing general formula?

• Example = Amino,aqua,di-chloro platinum (II)

1. Neutral

2. Positive

3. Negative

• [Pt(NH₃)(H₂O)(Cl)₂]⁰

Name the following Complex ions:

1. [V(H₂O)₆]³⁺

2. [Co(NH₃)₆]²⁺

3. [Co(Cl)₄]^2-

4. [Co(H₂O)₃(NH₃)₃]²⁺

1. Hexa Aqua Vanadium(III)

2. Hexa Ammine Cobalt (II)

3. Tetra Chloro Cobaltate (II)  → “-ate” for negative complex ions

4. Triammine,Triaqua Cobalt (II)

Which 3 metals have Square Planar complex ions - no matter what ligands are attached to them?

• What are the shapes of the rest

Platinum, Nickel, Palladium:

• All other metals have Octahedral shapes → square planar for large ligands 

When is a Square Planar complex ion:

• Cis

• Trans

• Cis = When identical ligands are on the same side (Left or right)

• Trans = When identical ligands are on the opposite side

When is Transplatin used?

Trans platin is more stable than Cisplatin, so it’s used when transporting → then it is converted to Cisplatin for cancer treatment

When is an Octahedral Complex ion:

• Cis

• Trans

• Cis = When identical ligands are 90^o from eachother (basically when 2 identical ligands are separated by one different ligand)

• Trans = When identical ligands are on opposite sides of eachother

What is:

• Polychromatic light

• Monochromatic light

• Polychromatic light = Contains mixture of wavelengths of light of different colours

• Monochromatic light = Contains one wavelength of light of the same colour

What are the gaps between orbitals equivalent to?

Frequency of light needed to excite electrons

Why are most compounds colourless?

Most compounds energy level split is too larger so light doesn’t hold enough energy to excite electrons

Why do Complex ions form coloured compounds?

When ligands datively covalently bond to ions, the metal ions d-orbitals split equally. The gap is small so wavelengths of light that are shone onto a sample can excite electrons from the lower half of the orbital to the upper half, when electrons de-excite they emit wavelengths of light with a corresponding colour

Why do few Complex ions not form coloured compounds?

• Example of a metal that doesn’t

When the d-orbital is full, there is no space for a lower electron to excite + occupy the orbital, so when light is shone, no colour is transmitted:

• Zinc

What is the relationship between Energy level gap of orbitals and frequency?

• Include in terms of colour of compound

Direct proportion:

• Higher frequency = Redder → Blue-er light absorbed

• Lower frequency = Blue-er → Redd-er light absorbed

What are the 2 formulae for the Energy between orbitals?

1. E = hf

2. E = hc/λ

• h → planck’s constant = 6.63 × 10^-34

What is the relationship of Oxidation state and Frequency?

• (+ colour observed)

Direct proportion = As oxidation number increases, it causes greater d-orbital splitting → higher frequency of light absorbed → bluer light absorbed

• Colour observed is less blue (cuz of complimentary colours)

(vice versa)

Order the following ligands in terms of D-Orbital splitting, Absorbed Frequency, Energy gap between orbitals, compound colour:

• NH₃

• H₂O

• Cl

> D - Splitting / Frequency + Energy change (increasing):

• Cl, H₂O, NH₃

> Colour (how blue it is): (Increasing)

• NH₃, H₂O, Cl

Order the following Co-ordination numbers in terms of D-Orbital splitting, Energy gap between orbitals, Colour:

• Octahedral (C.No = 6)

• Square Planar (C.No = 4)

• Tetrahedral (C.No = 4)

(+ WHAT DO YOU CONCLUDE BETWEEN SPLITTING + COLOUR)

> D - Splitting / Frequency + Energy change (increasing):

• Tetrahedral, Octahedral, Square Planar

> Colour (how blue it is → increasing):

• Square Planar, Octahedral, Tetrahedral

> More D-Orbital splitting means more redder colour (bluer light absorbed)

Explain the effect of Complex ion’s shape on its colour?

• What is the additonal factor

Ligands effects the geometry of molecules so effect the ions D-splitting:

• Type of metal ion

Colorimetry

Colorimetry

What is Colorimetry?

• 2 advantages

Use of light source + colour filter, shining the light at the sample with a complimenting colour to the light, then measuring the amount of light absorbed by the solution:

1. Quick process

2. Doesn’t require large sample

Give the 3 step method to carry out Colorimetry

1. We compare our sample absorption to know concentration + their absorption

2. Plot a graph of these values

3. Extrapolate the absorption from STEP 1 to the graph to find the corresponding concentration

What are the axis’ for a Calibration curve?

• x-axis = Concentration

• y-axis = Absorption

Why is their a plateau on Calibration curve?

Absorption not proportional to concentration

What is Complete ligand substitution?

Where all ligands are replaced

What is Incomplete ligand substitution?

Where a few ligands are replaced

What are the products of:

• [Co(H₂O)₆]²⁺ + 4Cl^-

• Why is this?

• Entropy of this reaction

[Co(H₂O)₆]²⁺ + 4Cl^- → [Co(Cl)₄]^2- + 6H₂O

• Cl is too large so can replace all 6 water ligands with 4 Cl

• High entropy since more products than reactants

What is a Bidentate Ligand? (co-ordinate number)

Singular Ligands that form 2 dative covalent bonds to a complex ion:

• 1 bidentate ligand = 2 co-ordinate number

What is prefix for the following Complex ions:

• 2 bidentates

• 3 bidentates

• 4 bidentates

1. 2 bidentates = Bis

2. 3 bidentates = Tris

3. 4 bidentates = Tetrakis

What is the structure of the “en” ligand?

• Type of ligand

• Charge

C₂H₄(NH₂)₂

• Bidentate

• Charge = 0

What is the structure of the Oxylate ligand?

• Type of ligand

• Charge

C₂O₄^2-

• Bidentate

• Charge = -2

What type of Isomerism do Complex ions observe?

• Exceptions

Optical Isomers → enantiomers of eachother:

• Linear/Square planar ions

What is the Chelate effect?

The replacement of monodentate ligands to multidentate ligands, such that entropy increases

Comment + Explain on the following about the Chelate effect:

• Entropy

• Feasibility

Entropy increases as the number of reactants < products. So entropy of forward reaction is high - meaning reaction is likely to occur + since enthalpy = 0 (as similar amount of bonds broken=formed)→ reaction is always feasible

What is EDTA?

• Number of lone pairs, atoms and charge

• Entropy → its effect

A multidentate ligands with:

• 4O:^- and 2N: so one EDTA replaces 6 ligands, -4 charge 

• High entropy of 2 reactants to 7 products → quickly reacts

What is the use of EDTA? (explain)

Prevention of lead poisoning in body, large entropy so feast reaction which quickly halts the effect of Pb poison in the body by forming harmless complex ions with Pb

What is Haem?

• Describe structure

• Bonds formed

• What is bonds with

Haem is an Fe(II) complex with multidentate ligand that can form 4 dative covalent bonds:

• Bonds with protein globin

• Forms Haemoglobin complex

What does the Haemoglobin complex can do? (use)

Forms co-ordinate bonds with O₂ + H₂O ligands which are easily formed + broken:

• Respiration

Explain how Haemoglobin work with Oxygen, Water and Carbon Dioxide

Haem forms weak co-ordinate bonds with oxygen, water and carbon dioxide so easily transports to + from muscles. Don’t form stable bonds with Fe²⁺

Explain how CO poisoning with Haemoglobin occur

CO forms stable bonds w/ Haem so decreased number of useable Haem for respiration meaning no Oxygen absorption, and increased Carbon Dioxide + CO in blood leading to death

Transition Metals as Catalysts

Transition Metals as Catalysts

What is a Heterogenous Catalyst?

• Example

A catalyst in a different phase to the reactants:

• Haber Cycle:
  N₂ + 3H₂ ⇌ 2NH₃ (Fe catalyst)

How do Heterogenous Catalyst work?

The reactant molecules adsorb, onto the catalysts surface + break the bonds of the reactants, to increase their reactivity for them to form products + react on the surface. The products then desorb off the surface

What is a Homogenous Catalyst?

• Example

A catalyst in the same phase as the reactants:

• Hydrogen Peroxide decomposition:
  2H₂O₂(aq) → O₂ + 2H₂O - - - - HBr (aq) catalyst

How do Homogenous Catalysts work?

The catalysts reacts with reactants to form an intermediate, which reacts with other reactants to form the final product, where the catalyst is regenerated

What is the role of Heterogenous surface?

• Area effect

Heterogenous catalyst contains several active site, where molecules adsorb, decreasing Activation energy, meaning more reactant can react on the surface + desorb as product

• Increase area = More active sites = Increased RoR

How do we increase the effect of a Heterogenous Catalyst (why):

• 2 ways to do this

Increase Surface Area , increasing the number of active sites:

1. Powder the catalyst

2. Coat the container or material with a large Surface area with a layer of catalytic material (reduce cost + increases yield)

What is the Contact Process?

• Purpose

• Overall equation

• Catalyst type

Formation of SO₃ and reacting w/ H₂SO₄ + H₂O to form a larger yield of H₂SO₄:

• Form higher yield of Sulfuric Acid

• SO₂(g) + 1/2O₂ ⇌ SO₃ - - - - (with V₂O₅ catalyst)

• Heterogenous Vanadium Oxide catalyst

Give the 2 equations for the Contact process involving the catalyst

• Type of reaction for each equation

1. SO₂ + V₂O₅ → SO₃ + V₂O₄ - - - - [Product formation]

2. V₂O₄ + 1/2O₂ → V₂O₅ - - - - [Catalyst Regeneration]

How does V₂O₅ work to catalyse the reaction in the Contact Process? (2 ways)

• Catalyst uses variable oxidation states to product alternate reaction routes that requires lower Activation energy

• Provides solid surface active sites to further decrease Activation energy

What happens to Vanadium + Sulfur in the contact process for Product formation?

• Sulfur → Oxidises

• Vanadium → Reduces

What happens to Vanadium in the contact process for Catalyst regeneration?

• Vanadium → Oxidises

What are the 2 half equations that occur from the Sulfur trioxide we form from the contact process to form Sulfuric Acid?

1. SO₃(g) + H₂SO₄(l) → H₂S₂O₇(l)

2. H₂S₂O₇(l) + H₂O(l) → 2H₂SO₄(l)

Why don’t we react SO₃ directly with water?

Reacting SO3 with water forms very hot Sulfuric acid and hard to control

What is Catalyst Poisoning? (+harm)

Industrially, reactions contain impurities which can adsorb onto the catalyst + dont react. Blocking active sites + preventing further reactions:

• Harm = Catalysts → like Pt, can be costly so hard to replace

How can we prevent Catalyst Poisoning?

• Give 2 specific examples

Carry out reactions to remove the impurities:

• Cleaning = Spraying water to remove dust

• Desulfurizing = Use ZnO to remove Sulfur contaminates 

What is the Production of Iodide?

• Overall equation 

• Catalyst + type

• Effect on reaction

• S₂O₈^2-(aq) + 2I^-(aq) → 2SO₄^2-(aq) + I₂(aq)

• Fe²⁺ catalyst → Homogenous catalyst

• The positive charge of the Iron catalyst, attracts the 2 negatively charged reactants to start the reaction

Give the 2 half equations that occur in the Production of Iodide?

1. S₂O₈^2-(aq) + Fe²⁺(aq) → 2SO₄^2-(aq) + 2Fe³⁺(aq)

2. 2Fe³⁺(aq) + 2I^-(aq) → 2Fe²⁺(aq) + I₂(aq)

What happens to S₂O₈^2- + Fe²⁺ in the Production of Iodide for Product formation?

• Sulfur = Reduces

• Iron = Oxidises

What happens to Fe²⁺ and I^- in the Production of Iodide for Catalyst regeneration?

• Iron = Reduces

• Iodide = Oxidises

How does Fe²⁺ act as a Catalyst?

• Attracts reactants to speed up reaction

• Provides variable oxidation states decreasing Ea + alternative routes

Autocatalysis

Autocatalysis

What is Autocatalysis?

When a reaction produces its own catalyst:

Give an example of an autocatalysis equations:

• Catalyst

Mn²⁺ catalysis:

• Mn²⁺ is a catalyst

Describe an autocatalysis graph of Mn²⁺

• Initially due to like charges the negatively charged reactants repel, increasing Activation energy + decreasing RoR

• Eventually they react + form Mn²⁺ which acts as a catalyst (autocatalysis) → so the RoR increases, making the graph line steep

• At the end it plateaus due to reactants being used up

Give the Overall equation for the Catalysis of Manganate ions

2MnO₄^- + 5C₂O₄^2- + 16H⁺ → 2Mn²⁺ + 10CO₂ + 8H₂O:

• Mn²⁺ catalyst

Give the 2 half equations for the Catalysis of Manganate ions

• What is being reduced + oxidised

1. 8Mn²⁺ + 2MnO₄^- + 16H⁺ → 10Mn³⁺ + 8H₂O:
   - Reduced = Mn (from MnO₄)
   - Oxidised = Mn (from Mn²⁺)

2. 10Mn³⁺ + 5C₂O₄^2- → 10Mn²⁺ + 10CO₂:
   - Reduced = Mn reduced
   - Oxidised = C oxidised

Vanadium Oxidation states

Vanadium Oxidation states

Comment on the Transition metals oxidation states

• Exceptions

All transition metals have variable oxidation states:

• Silver + Mercury dont have variable oxidation states

What are the 4 oxidation states of Vanadium?

• V²⁺

• V³⁺

• V⁴⁺

• V⁵⁺

What are the reactants for the Vanadium rainbow?

NH₄VO₃(aq) + Zn → 5 different compounds

What are the 5 different compounds in the Vanadium rainbow?

• Include their colours

• Vanadium oxidation states

• Trend down the colours

• Yellow = [VO₂(H₂O)₄]⁺ - - - V = +5

• Green = Mix of yellow + blue compounds

• Blue = [VO(H₂O)₅]²⁺ - - - V = +4

• Dark green = [V(H₂O)₆]³⁺ - - - V= +3

• Purple = [V(H₂O)₆]²⁺ - - - V= 2+

→ As colour changes from yellow to purple, Vanadium reduces

What are the Vanadium half equations with Zinc from:

1. Yellow → Blue

2. Blue → Dark green

3. Dark green → Purple

1. VO₂⁺ + 2H⁺ + e^- → VO²⁺ + H₂O  - - -  (Yellow → Blue)

2. VO²⁺ +  2H⁺ + e^- → V³⁺ + H₂O  - - -  (Blue → Dark Green)

3. V³⁺ + e^- → V²⁺  - - -  (Dark Green → Purple)

What is the Zinc half equation?

Zn → Zn²⁺ + 2e^-

How do Zn react with Vanadium? (in terms of electrode potential)

All the Vanadium reactions are more positive (electrode potential), than Zinc reduction so always reacts

***LOOK AT VANADIUM RAINBOW CALCULATIONS NOTES 1***

***LOOK AT VANADIUM RAINBOW CALCULATIONS NOTES 1***

What are the 4 Redox Titrations that are useful to memorise?

1. C₂O₄^2- : MnO₄^- → 5:2 ratio

2. Fe²⁺ : MnO₄^- → 5:1 ratio

3. Cr₂O₇^2- : Fe²⁺ → 1:6 ratio

4. S₂O₃^2- : I₂ → 2:1 ratio

***IMPURE STARTING MATERIALS IN NOTES 1***

***IMPURE STARTING MATERIALS IN NOTES 1***

Complex Ions in aq solutions

Complex Ions in aq solutions

What is a Metal Aqua ion?

• When is it formed

A complex ion containing water ligands ONLY: 

• When a salt is dissolved in water

What are the 4 “main” Metal Aqua ions?

• Colour for each

• [Fe(H₂O)₆]²⁺ = Green solution

• [Cu(H₂O)₆]²⁺ = Blue solution

• [Fe(H₂O)₆]³⁺ = Pale violet solution

• [Al(H₂O)₆]³⁺ = Colourless solution

Give the products of the following equation:

• FeCl₃ + 6H₂O

• 2FeCl₃ + 6H₂O → 2[Fe(H₂O)₆]³⁺ + 3Cl^-

What are the pH of the Metal aqua ions? (why)

All have a pH<7, so are all acidic:

• Since they all donate protons in solution

What is the general equation for Metal Aqua ions with water?

[X(H₂O)₆]ⁿ + H₂O ⇌ [X(OH)(H₂O)₅]^n-1 + H₃O⁺

What dictates a Metal Aqua Ion’s acidity (how)

Higher +ve Central Metal ion = More acidic:

• Higher +ve means electrons are more attracted to the nucleus

• Nuclear radius is smaller as charge increases, charge density increases so electrons in bonds are attracted stronger to the more +ve metal ion so Hydrogens, in the water ligands, so greater partial positive charge so are taken easier by the polar water molecules forming H₃O⁺ → making it more acidic

What is more acidic:

• [Al(H₂O)₆]³⁺ or [Fe(H₂O)₆]³⁺

• Why

Al is more acidic:

• Al is in a higher period - so atomic radius is lower, so charge density is greater than Fe → making it more acidic

What 4 solutions can react with Metal Aqua Ions?

1. NaOH(aq)

2. NH₃(aq)

3. Na₂CO₃(aq)

4. HCl (aq)

What is the general equation of a Metal Aqua Ion with NaOH?

• Where X is a Metal Aqua ion

  • For 2+ and 3+ MAI

• 2+ ions = [X(H₂O)₆]²⁺ + OH^- → [X(OH)₂(H₂O)₄] + 2H₂O

• 3+ ions = [X(H₂O)₆]³⁺ + OH^- → [X(OH)₃(H₂O)₃] + 3H₂O

What are the 4 colours of the MAI reacted from NaOH?

• In excess NaOH

• [Fe(H₂O)₄(OH)₂] = Green → No change in excess

• [Cu(H₂O)₄(OH)₂] = Blue → No change in excess

• [Fe(H₂O)₃(OH)₃] = Brown → No change in excess

• [Al(H₂O)₃(OH)₃] = White → forms [Al(H₂O)₃(OH)₄]^- to be colourless

What happens to the Fe(OH)₂(H₂O)₄ when exposed to air?

• Formed from NaOH

Turns from green to brown from oxidation to [Fe(H₂O)₃(OH)₃]

What makes [Al(H₂O)₃(OH)₃] different to other MAI’s?

• What is the usual property of MAI’s

Amphoteric:

• All can be reacted with acids (H₃O⁺) to form the MAI ion [X(H₂O)₆]

What are the 2 Amphoteric reactions of Al(OH)₃(H₂O)₃?

Acidic:

• Al(OH)₃(H₂O)₃ + 3H₃O⁺ ⇌ [Al(H₂O)₆]³⁺ + 3H₂O

Basic:

• Al(OH)₃(H₂O)₃ + OH^- → [Al(OH)₄(H₂O)₂]^- + H₂O