Redox Reactions of Transition Metals

Oxidation of Transition Metals

Transition metal ions can undergo oxidation reactions. Remember that an "oxidation is a loss" of electrons.

Illustrative background for Oxidation of Fe<sup>2+</sup> to Fe<sup>3+</sup>

Illustrative background for Oxidation of Fe<sup>2+</sup> to Fe<sup>3+</sup> ?? "content

Oxidation of Fe²⁺ to Fe³⁺

Iron (II) ions can be oxidised by potassium manganate (VII) solution in acidic conditions.
- The observed colour change is from green to brown.
- Iron is oxidised from oxidation state +2 to +3.
- Manganese is reduced from oxidation state +7 to +2.

$Illustrative background for Half-equation to equation$ $Illustrative background for Half-equation to equation ?? "content$

Half-equation to equation

You need to understand how to construct an equation from the half-equations. Consider these two half-equations:
- Fe²⁺ → Fe³⁺ + e^-
  MnO₄^- + 8H⁺ + 5e^- → Mn²⁺ + 4H₂O
One e^- is produced with Fe³⁺ and five e^- are in the reactants of the MnO₄^- half-equation.
- You therefore need five times more of the first half-equation.
MnO₄^- + 8H⁺ + 5Fe²⁺ → Mn²⁺ + 4H₂O + 5Fe³⁺

Illustrative background for Oxidation of Cr<sup>3+</sup> to Cr<sub>2</sub>O<sub>7</sub><sup>2-</sup>

Illustrative background for Oxidation of Cr<sup>3+</sup> to Cr<sub>2</sub>O<sub>7</sub><sup>2-</sup> ?? "content

Oxidation of Cr³⁺ to Cr₂O₇^2-

Cr³⁺ in an excess of OH^- ions (from NaOH) exists in the complex ion [Cr(OH)₆]^3-.
This complex ion and be oxidised with H₂O₂:
- 2[ Cr(OH)₆ ]^3- + 3H₂O₂ → 2CrO₄^2- + 2OH^- + 8H₂O
The colour changes observed are from purple to green when excess NaOH is added and from green to yellow when H₂O₂ is added.

CrO₄^2- to Cr₂O₇^2-

A reversible reaction can be used to easily change between CrO₄^2- and Cr₂O₇^2-:
- CrO₄^2- $\;\xrightleftharpoons[add\; OH^-]{add\;H^+}\;$ Cr₂O₇^2-
- Use dilute sulphuric acid and sodium hydroxide to push the equlibrium to either side.

Colour change and oxidation states

The colour change obeserved is from yellow (CrO₄^2-) to orange (Cr₂O₇^2-).
Chromium is oxidised from oxidation state +3 to +6.
Oxygen is reduced from oxidation state -1 to -2.

Reduction of Transition Metals

Transition metal ions can undergo reduction reactions. Remember that a "reduction is a gain" of electrons.

Reduction of iron (III) to iron (II)

Iron (III) ions can be reduced by using aqueous iodide ions as the reducing agent.
- The observed colour change is from brown to green.

The equation

Fe³⁺ + 2I^- → 2Fe²⁺ + I₂
- Iron is reduced from oxidation state +3 to +2.
- Iodine is oxidised from oxidation state -1 to 0.

Reduction of chromium (VI) to chromium (III)

Cr₂O₇^2- can be reducted with zinc in an acidic solution.
- Cr₂O₇^2- + 14H⁺ + 3Zn → 2Cr³⁺ + 7H₂O + 3Zn²⁺
A colour change from orange to green is observed.
- Chromium is reduced from oxidation state +6 to +3.
- Zinc is oxidised from oxidation state 0 to +2.

Reduction of copper (II) to copper (I)

Cu²⁺ can be reduced by iodide ions. In the process, the iodide ions are oxidised by the copper (II).
- 2Cu²⁺_(aq) + 4I^- → 2CuI_(s) + I_{2 (aq)}

Colour change and oxidation states

A colour change from orange to brown. An off-white precipitate of copper (I) iodide settles in the solution over time.
- Copper is reduced from oxidation state +2 to +1.
- Iodine is oxidised from oxidation state -1 to 0.

Disproportionation

Disproportionation occurs when an element both oxidises and reduces in a reaction.

Disproportionation of copper (I)

In solution, copper (I) ions (oxidation state +1) forms solid copper (oxidation state 0) and copper (II) ions (oxidation state +2).
- It is therefore both reduced and oxidised in the solution.
2Cu⁺_(aq) → Cu_(s) + Cu²⁺_(aq)

Example of disproportionation

Copper (I) oxide can be dissolved in dilute sulphuric acid in a disproportionation reaction:
- Cu₂O_(s) + H₂SO_{4 (s)} → Cu_(s) + CuSO_{4 (aq)} H₂O_(l)
Copper goes from oxidation state +1 in Cu₂O_(s) to oxidation state 0 in Cu_(s) and oxidation state +2 in CuSO_{4 (aq)}.
- The copper (I) has been both reduced and oxidised.

1Principles of Science I

1.1Structure & Bonding

1.1.1Atomic Model

1.1.2Electron Shells, Sub-Shells & Orbitals

1.1.3Ionic Bonding

1.1.4Representing Ionic Bonds

1.1.5Covalent Bonding

1.1.6Representing Covalent Bonds

1.1.7Metallic Bonding

1.1.8Intermolecular Forces

1.1.9Intermolecular Forces 2

1.1.10End of Topic Test - Bonding

1.1.11Relative Masses

1.1.12The Mole

1.1.13Molar Calculations

1.1.14Molar Calculations 2

1.1.15Empirical & Molecular Formulae

1.1.16Balanced Equations

1.1.17Percentage Yield

1.1.18End of Topic Test - Amount of Substance

1.2Properties of Substances

1.2.1The Periodic Table

1.2.2Ionisation Energy

1.2.3Factors Affecting Ionisation Energies

1.2.4Trends of Ionisation

1.2.5Trends in the Periodic Table

1.2.6Polarity

1.2.7Metals & Non-Metals

1.2.8Alkali Metals

1.2.9Alkaline Earth Metals

1.2.10Reactivity of Alkaline Earth Metals

1.2.11Redox

1.2.12Transition Metals

1.2.13Redox Reactions of Transition Metals

1.3Cell Structure & Function

1.3.1Introduction to Cells

1.3.2Prokaryotes

1.3.3Organelles of Eukaryotic Cells

1.3.4Organelles of Eukaryotic Cells 2

1.3.5Organelles in Plant Cells

1.3.6Microscopy

1.3.7End of Topic Test - Cell Structure

1.4Cell Specialisation

1.4.1Cell Specialisation

1.4.2Blood Cells

1.4.3Plant Cells

1.4.4Gametes

1.5Tissue Structure & Function

1.5.1Human Gas Exchange

1.5.2Blood Vessels

1.5.3Atherosclerosis

1.5.4Skeletal Muscle

1.5.5Slow & Fast Twitch Fibres

1.5.6Neurones

1.5.7Speed of Transmission

1.5.8Action Potentials

1.5.9End of Topic Test - Neurones & Action Potentials

1.5.10Synapses

1.5.11Types of Synapse

1.5.12Medical Application

1.5.13End of Topic Test - Synapses

1.5.14Chemical Brain Imbalances

1.5.15Effect of Drugs on the Brain

1.6Working with Waves

1.6.1Progressive Waves

1.6.2Wave Speed & Phase Difference

1.6.3Longitudinal & Transverse Waves

1.6.4Stationary Waves

1.6.5Stationary Waves 2

1.6.6Applications of Stationary Waves

1.6.7Interference

1.6.8Diffraction

1.6.9Diffraction Gratings

1.6.10Application of Diffraction Gratings

1.7Waves in Communication

1.7.1Refraction at a Plane Surface

1.7.2Internal Reflection & Fibre Optics

1.7.3Applications of Total Internal Reflection

1.7.4Properties

1.7.5Gamma, X-Ray & UV Light

1.7.6Visible Light

1.7.7Infrared, Microwave & Radio Waves

1.7.8Intensity

1.7.9Digital & Analogue Signals

1.7.10Communication Channels

2Practical Scientific Procedures and Techniques

2.1Titration

2.1.1pH Curves & Titrations

2.1.2pH Curves & Titrations 2

2.1.3Buffer Solutions

2.2Colorimetry

2.2.1Measuring Rates

2.2.2Beer-Lambert Law

2.3Chromatography

2.3.1Overview of Chromatography

2.3.2Thin-Layer Chromatography

2.3.3Column Chromatography

2.3.4Gas Chromatography

3Science Investigation Skills

3.1Scientific Processes

3.1.1Aims, Hypotheses & Sampling

3.1.2Pilot Studies & Design

3.1.3Ethics

3.1.4Variables & Control

3.1.5Demand Characteristics & Investigator Effects

3.1.6Features of Science

3.1.7Scientific Report

3.1.8Scientific Report 2

3.2Data Handling & Analysis

3.2.1Types of Data

3.2.2Descriptive Statistics

3.2.3Presentation & Display of Data

3.3Enzymes in Action

3.3.1Overview of Protein Structure

3.3.2Enzymes

3.3.3Factors Affecting Enzyme Activity

3.3.4Enzyme-Controlled Reactions

3.4Diffusion

3.4.1Diffusion

3.5Plants & Their Environment

3.5.1Factors Affecting Plant Growth

3.5.2Measuring Number & Distribution of Species

3.6Energy Content in Fuels

3.6.1Fractions

3.6.2Burning Hydrocarbons

3.6.3Combustion

3.6.4Energy

3.6.5Energy at Home

3.6.6Calorimetry

3.7Electrical Circuits

3.7.1Circuit Diagrams & Components

3.7.2Diodes, LDRs & Thermistors

3.7.3Resistance

3.7.4Electrical Work

3.7.5Ohm's Law

3.7.6Domestic Uses of Electricity

3.7.7Fuses

4Principles of Science II

4.1Extracting Elements

4.1.1Atom Economy

4.2Relating Properties to use of Substances

4.2.1Group 2 Chemistry

4.2.2End of Topic Test - Group 2

4.2.3Electrolysis

4.2.4Electrolysis Examples

4.2.5Extracting Metals

4.2.6Transition Metals

4.2.7Variable Oxidation States

4.2.8Heterogeneous Catalysts

4.2.9Homogeneous Catalysts

4.3Organic Chemistry

4.3.1Naming Compounds

4.3.2Functional Groups

4.3.3Isomerism

4.3.4Hydrocarbons

4.3.5Structure of Alkanes

4.3.6Boiling Points of Alkanes

4.3.7Alkenes

4.3.8Curly Arrows & Mechanisms

4.3.9Cracking

4.3.10Combustion

4.3.11Free Radical Substitution of Alkanes

4.3.12Electrophilic Addition of Alkenes

4.4Energy Changes in Industry

4.4.1The Kelvin Scale

4.4.2Enthalpy Changes

4.4.3Calorimetry

4.4.4Bond Enthalpies

4.4.5Hess' Law

4.5The Circulatory System

4.5.1The Circulatory System

4.5.2Blood Vessels

4.5.3Blood Transfusion & the ABO Rhesus System

4.5.4The Heart

4.5.5The Cardiac Cycle

4.5.6Cardiac Output

4.5.7Coordination of Heart Action

4.5.8Heart Dissection

4.5.9Controlling Heart Rate

4.5.10Electrocardiograms

4.5.11Cardiovascular Disease

4.5.12Investigating Heart Rates

4.6Ventilation & Gas Exchange

4.6.1Human Gas Exchange

4.6.2Ventilation

4.6.3Measuring Gas Exchange

4.6.4Controlling Ventilation Rate

4.6.5Lung Disease

4.6.6Lung Disease Data

4.7Urinary System

4.7.1Kidneys & Control of Water Balance

4.7.2Kidneys & Osmoregulation

4.7.3Kidneys & Blood Pressure

4.7.4Urine

4.7.5Kidney Failure & Urinalysis

4.7.6Dialysis

4.7.7Transplants

4.8Cell Transport

4.8.1Cell Membrane Structure

4.8.2Diffusion

4.8.3Osmosis

4.8.4Active Transport

4.9Thermal Physics

4.9.1Power & Efficiency

4.9.2Work & Energy

4.9.3Conservation of Energy

4.9.4Pressure

4.9.5First Law of Thermodynamics

4.9.6Second Law of Thermodynamics

4.9.7Heat Engines, Heat Pumps & Refrigerators

4.9.8Non-Flow Processes

4.9.9p-V Diagrams

4.9.10Ideal Gases

4.9.11Ideal Gases 2

4.9.12Thermal Energy Transfer

4.9.13Thermal Energy Transfer Experiments

4.10Materials

4.10.1Density

4.10.2Stress & Strain

4.10.3Properties of Materials

4.10.4Elasticity

4.10.5Plasticity

4.10.6Energy in Materials

4.10.7Young Modulus

4.11Fluids

4.11.1Fluid Flow

4.11.2Viscosity

4.11.3Density

4.11.4Continuity Equation

4.11.5Bernoulli's Equation

4.11.6Non-Newtonian Fluids

5Contemporary Issues in Science

5.1Contemporary Issues in Science

5.1.1Sustainability

5.1.2Genetic Engineering

5.1.3Uses of Genetic Modification

5.1.4Stem Cell Therapy

5.1.5Cloning

5.1.6Cloning 2

5.1.7Nanotechnology

5.1.8Ecosystems

5.2Analysing Scientific Information

5.2.1Validity

5.2.2Peer Review

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