6.6.4

Oxidation States & Equations

Test yourself on Oxidation States & Equations

After reading these notes, test your knowledge with free interactive questions on Seneca — used by over 10 million students.

Oxidation States and Redox

Oxidation states are crucial tools for understanding redox reactions.

Oxidation states

Oxidation states

  • An oxidation state shows how many electrons an atom has gained or lost.
  • The concept of oxidation state is related to electronegativity.
    • Electronegativities can be used to work out oxidation states.
  • There are a set of rules to assigning oxidation states - these will be unpacked in the next slide.
Rules

Rules

  • To assign oxidation states in a compound with multiple elements, we pretend every bond is ionic (even when they're definitely not)!
    • We ask the question 'which element is going to take the electron pair?'
    • The answer is, the most electronegative one!
  • This gives us our first rule:
    • In a compound with fluorine, fluorine's oxidation state is always -1.
Oxygen

Oxygen

  • The oxidation state of oxygen is always -2.
    • Unless you have a compound of oxygen and fluorine. The fluorine rule takes priority.
    • Another exception is in a peroxide (e.g. Na2O2).
Hydrogen

Hydrogen

  • Hydrogen always has an oxidation state of +1.
    • Except in metal hydrides e.g. NaH, where it is -1.
The rest

The rest

  • In a compound ion, the overall oxidation state is equal to the charge on the ion.
  • In a simple ion, the oxidation state is just the charge on the ion.
  • In a pure element, the oxidation state is zero. This includes atoms like He, but also molecules like H2.
  • Oxidation states are commonly represented by Roman numerals e.g. Fe(III) sulfate means (Fe3+)2(SO42-)3.

Ionic Half-Equations

You will already be familiar with balanced equations. When the reaction is a redox reaction, we can make some further adjustments.

Ionic half-equations

Ionic half-equations

  • An ionic half equation shows either reduction or oxidation.
    • An example is: O2 + 4e- →\rightarrow 2O2-
    • This is the ionic half equation for the reduction of O2 to 2O2-
  • If you have ionic half equations for both a reduction process and an oxidation process, you can add the two to generate a full balanced equation.
An example: TiCl<sub>4</sub>

An example: TiCl4

  • The ionic half equation for the oxidation of Ti →\rightarrow Ti4+ is:
    • Ti →\rightarrow Ti4+ + 4e-
  • The ionic half equation for the reduction of Cl2 →\rightarrow to 2Cl- is:
    • Cl2 + 2e- →\rightarrow 2Cl-
  • When adding the two equations together, you must balance the number of electrons on either side so that they cancel out.
    • 2Cl2 + 4e- →\rightarrow 4Cl-
    • Ti →\rightarrow Ti4+ + 4e-
  • So the full balanced equation is:
    • Ti + 2Cl2 →\rightarrow Ti4+ + 4Cl-
Jump to other topics
1

Structure - Models of the Particulate of Matter

1.1

Introduction to the Particulate Model of Matter

1.1.1States of Matter1.1.2Kinetic Molecular Theory1.1.3Simple Sphere1.1.4Changing State1.1.5Forces Between Particles1.1.6Changes of State1.1.7Predicting States1.1.8Changing State HyperLearning1.1.9Ionization Energy
1.2

The Nuclear Atom

1.2.1Fundamental Particles1.2.2Isotopes & Mass Number1.2.3Mass Spectrometry1.2.4Mass Spectrometry1.2.5Mass Spectroscopy - Analysis1.2.6Extended Response - Mass Spectrometry1.2.7Radioactivity
1.3

Electron Configuration

1.3.1Electron Shells, Sub-Shells & Orbitals1.3.2Electron Configuration1.3.3Absorption & Emission Spectra1.3.4IB Multiple Choice - Atomic Structure1.3.5Extended Response - The Atom & Electrons
1.4

Counting Particles by Mass: The Mole

1.4.1Relative Masses1.4.2The Mole1.4.3IB Multiple Choice - Moles
1.5

Ideal Gases

1.5.1Ideal Gas Equation1.5.2Gas Laws1.5.3IB Multiple Choice - Gases & Kinetics
1.6

Elements, Compounds & Mixtures

1.6.1Fundamental Particles1.6.2Pure Substances1.6.3Purity & The Law of Definite Proportion1.6.4Mixtures1.6.5Separating Mixtures1.6.6IB Multiple Choice - Pure Substances1.6.7Extended Response - Moles & Pure Substances
1.7

States of Matter & Changes of State

1.7.1States of Matter1.7.2Particle Diagrams1.7.3IB Multiple Choice - Solids, Liquids, & Gases1.7.4Balancing Equations & Ionic Equations1.7.5Empirical & Molecular Formulas
1.8

Reacting Masses &. Volumes

1.8.1Balancing Equations & Ionic Equations1.8.2Percentage Yield
1.9

Solutions

1.9.1Molarity1.9.2Particulate Model of Solutions
2

Structure - Models of Bonding & Structure

2.1

The Ionic Model

2.1.1Ionic Bonding
2.2

The Covalent Model

2.2.1Covalent Bonds2.2.2Complex Ions2.2.3Factors Affecting Covalent Bond Strength2.2.4Polarity
2.3

Covalent Structures

2.3.1Ionic Lewis Structures2.3.2Covalent Lewis Structures2.3.3VSEPR Theory2.3.4Resonance Structures2.3.5Allotropes of Carbon2.3.6Formal Charge2.3.7End of Topic Quiz - Bonding2.3.8IB Multiple Choice - Bonding & Lewis Structures2.3.9IB Multiple Choice - Resonance & Formal Charge
2.4

The Metallic Model

2.4.1Metallic Bonding
2.5

From Models to Materials

2.5.1Alloys2.5.2Properties of Polymers2.5.3Polymerisation Reactions2.5.4Introduction to Alkenes2.5.5Reactions of Alkenes2.5.6End of Topic Quiz - Alkenes
2.6

Valence Electrons & Ionic Compounds

2.6.1Valence Electrons & Forming Ions2.6.2Ionic Compounds2.6.3End of Topic Quiz - Atoms & Ions2.6.4IB Multiple Choice - Valence & Ions
2.7

Molecular Shape

2.7.1VSEPR2.7.2Molecular Shapes2.7.3Bond Hybridization2.7.4IB Multiple Choice - VSEPR & Bond Hybridization2.7.5Extended Response - Bonding & Molecular Shape
2.8

Intermolecular Forces

2.8.1Introduction to Intermolecular Forces2.8.2London Dispersion Forces2.8.3Dipole-Dipole Interactions2.8.4Ion-Dipole Interactions2.8.5Hydrogen Bonding2.8.6Large Biomolecules2.8.7IB Multiple Choice - Intermolecular Forces2.8.8Extended Response - Hydrogen Bonding
3

Structure - Classification of Matter

3.1

The Periodic Table: Classification of Elements

3.1.1The Periodic Table3.1.2Trends in the Periodic Table3.1.3End of Topic Quiz - Periodicity & Trends3.1.4Periodic Trends - Electronegativity & Affinity3.1.5End of Topic Quiz - Periodic Trends3.1.6IB Multiple Choice - Periodic Trends3.1.7Extended Response - Periodic Table
3.2

Periodic Trends

3.2.1Atomic & Ionic Radii3.2.2Ionisation & Electronegativity3.2.3Metallic Behaviour & Oxides3.2.4Period 3 Elements & Oxides3.2.5Period 3 Oxides3.2.6End of Topic Quiz - Period 33.2.7Periodic Trends: Blocks3.2.8Redox Chemistry
3.3

Group 1 Alkali Metals

3.3.1Alkali Metals
3.4

Halogens

3.4.1Introduction to Halogens3.4.2Reactions of Halogens3.4.3Chlorine & Chlorate(I)3.4.4End of Topic Quiz - Group 73.4.5Exam-Style Question - Group 73.4.6End of Topic Quiz - Periodicity, Group 2 & 7
3.5

Noble gases, group 18

3.5.1Noble Gases
3.6

Functional Groups: Classification of Organic

3.6.1Nomenclature3.6.2Trends in Physical Properties3.6.3Saturated & Unsaturated Hydrocarbons3.6.4Nomenclature contd.3.6.5Types of Formulas3.6.6Isomerism3.6.7Formulae3.6.8Homologous Series3.6.9Structural Isomers
3.7

Functional Group Chemistry

3.7.1Degrees of Substitution3.7.2Arenes
3.8

Alkanes

3.8.1Alkanes3.8.2Fractional Distillation3.8.3Cracking3.8.4Combustion3.8.5Chlorination3.8.6End of Topic Quiz - Alkanes
3.9

Alcohols

3.9.1Production of Alcohols3.9.2Oxidation of Alcohols3.9.3Oxidation of Alcohols - 23.9.4Elimination Reactions3.9.5End of Topic Quiz - Alcohols3.9.6Exam-Style Question - Alcohols
3.10

Halogenoalkanes

3.10.1Substitution Reactions3.10.2Elimination Reactions3.10.3Ozone Depletion3.10.4End of Topic Quiz - Halogenoalkanes
4

Reactivity - What Drives Chemical Reaction?

4.1

Endothermic & Exothermic Reactions

4.1.1Endothermic & Exothermic Reactions4.1.2Energy Diagrams4.1.3Heat Transfer & Thermal Equilibrium4.1.4IB Multiple Choice - Enthalpy & Energy
4.2

Enthalpy of Reaction, Formation, & Hess' Law

4.2.1Enthalpy of Reaction4.2.2Bond Enthalpies4.2.3Enthalpy of Formation4.2.4Hess’ Law4.2.5Thermodynamics & Kinetic Control4.2.6End of Topic Quiz - Thermodynamics4.2.7IB Multiple Choice - Enthalpy4.2.8Extended Response - Enthalpy Change
4.3

Entropy

4.3.1Introduction to Entropy4.3.2Absolute Entropy & Entropy Change4.3.3Free Energy4.3.4Thermodynamically Favorable Reactions4.3.5IB Multiple Choice - Entropy & Free Energy4.3.6Extended Response - Free Energy
5

Reactivity - How Much, How Fast & How Far?

5.1

Kinetics

5.1.1Collision Theory & Rates of Reaction5.1.2Maxwell-Boltzmann Distribution5.1.3Increasing Rates5.1.4End of Topic Quiz - Kinetics
5.2

Rates of Reaction

5.2.1Rate Equations5.2.2Rate Equations 25.2.3The Effect of a Catalyst
5.3

Stoichometry

5.3.1Stoichiometry
5.4

Le Châtelier’s Principle

5.4.1Introduction to Le Châtelier’s Principle5.4.2Reaction Quotient & Le Châtelier’s Principle5.4.3Temperature & Le Châtelier’s Principle5.4.4IB Multiple Choice -Le Châtelier’s Principle5.4.5Extended Response - Le Châtelier
5.5

Introduction to Equilibrium

5.5.1Equilibrium & Equilibrium Graphs5.5.2Dynamic Equilibria5.5.3Reversible Reactions & Directions
5.6

Equilibrium Constant

5.6.1Calculating the Equilibrium Constant5.6.2Magnitude of the Equilibrium Constant5.6.3Properties of the Equilibrium Constant5.6.4Calculating Equilibrium Concentrations5.6.5Representations of Equilibrium5.6.6IB Multiple Choice - Equilibrium Constants5.6.7Extended Response - Calculating Kc
5.7

Reaction Quotient & Equilibrium Constant

5.7.1Reaction Quotient5.7.2Equilibrium Constants5.7.3Partial Pressures5.7.4Kp5.7.5IB Multiple Choice - Reaction Quotient & Kp5.7.6Extended Response - Kp & Bond Enthalpy
6

Reactivity - The Mechanisms of Chemical Change

6.1

Proton Transfer Reactions

6.1.1Brønsted-Lowry Theory
6.2

The pH Scale

6.2.1pH & pOH6.2.2Ionic Product of Water6.2.3Using Kw6.2.4IB Multiple Choice - pH & Kw6.2.5Extended Response - Kw
6.3

Strong & Weak Acids and Bases

6.3.1Strong Acids & Bases6.3.2Weak Acids & Ka6.3.3Weak Bases & Kb6.3.4Weak Acids & Bases Calculation Walkthrough
6.4

Acid Deposition

6.4.1Acid Deposition
6.5

Types of Organic Reactions

6.5.1Electrophilic Substitution
6.6

Oxidation & Reduction

6.6.1Oxidation Number Method6.6.2Winkler Method6.6.3Redox Reactions6.6.4Oxidation States & Equations6.6.5End of Topic Quiz - Redox6.6.6Extended Response - Redox Reactions
6.7

Electrochemical Cells

6.7.1Introduction to Electrochemical Cells6.7.2Galvanic Cells6.7.3Cell Notation6.7.4Electrolytic Cells6.7.5Extended Response - Voltaic Cells & Redox
6.8

Titration

6.8.1Redox Titrations6.8.2Titration Calculations6.8.3Atom Economy
6.9

Acid-Base Titrations

6.9.1Titration Calculation Weak Acid & Strong Base6.9.2Titration Experimental Detail6.9.3Extended Response - Titration6.9.4Titration Calculations6.9.5Titration Curves6.9.6Titration Calculation Strong Acid & Weak Base6.9.7IB Multiple Choice - Titrations6.9.8Polyprotic Acids6.9.9Titration Calculations Strong Acid & Strong Base6.9.10Titrations Curves 2
7

Measurement, Data Processing & Analysis

7.1

Uncertainties & Errors in Measurements & Results

7.1.1Qualitative & Quantitative data
7.2

Graphical Techniques

7.2.1Drawing & Interpreting Graphs7.2.2Linear Interpolation
7.3

Spectroscopic Identification of Organic Compounds

7.3.1Understanding NMR7.3.2Carbon-13 NMR7.3.3Hydrogen-1 NMR7.3.4Hydrogen-1 NMR 27.3.5End of Topic Quiz - NMR
7.4

Infrared Spectroscpy

7.4.1Infrared Spectroscopy

Practice questions on Oxidation States & Equations

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
    Two exceptions where oxygen does NOT necessarily have the oxidation state of -2:Fill in the list
  2. 2
    What is the oxidation state of Fe(II)?Multiple choice
  3. 3
    What is the overall oxidation state of the complex ion NO<sub>3</sub><sup>-</sup>?Multiple choice
  4. 4
    Reduction or oxidation?Fill in the list
  5. 5
    Two ionic half equations can be added together if which of the following conditions are met?Multiple choice
Answer all questions on Oxidation States & Equations

Unlock your full potential with Seneca Premium

  • Unlimited access to 10,000+ open-ended exam questions

  • Mini-mock exams based on your study history

  • Unlock 800+ premium courses & e-books

Get started with Seneca Premium

Redox Reactions

End of Topic Quiz - Redox