1.6.1

Electrochemical Cells

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Electrochemical Cells

An electrochemical cell can be used to make an electrical current.

A cell

A cell

How is a current made?

How is a current made?

There are two processes happening in a cell: oxidation and reduction.
- One metal is oxidised and gives up electrons.
- In the other side of the cell, the other metal accepts these electrons.
The electrons travel from one side of the cell to the other via the wire, which is the electrical current.

Electrodes

Electrodes

Often, you’ll use an electrode that is made of the same metals that are being oxidised or reduced.
But you don’t have to, and if one of your equations doesn’t involve a solid being formed or lost, you’ll need to use a different metal.
- In these circumstances, we use a platinum electrode because they are inert and so don’t tend to react with anything.

OIL RIG

OIL RIG

OIL RIG is a useful mnemonic for remembering the difference between oxidation and reduction:
- Oxidation Is Loss (of electrons).
- Reduction Is Gain (of electrons).

Half Equations and Reduction Potentials

Half equations show redox potentials.

Half equations

Half equations

An ionic half equation shows either reduction or oxidation.
- E.g. O₂ + 4e^- $\rightarrow$ 2O^2-
  - This is the ionic half equation for the reduction of O₂ to 2O^2-
If you have ionic half equations for a reduction process and an oxidation process, you can add the two to make a full balanced equation.

Reduction potentials

Reduction potentials

By convention, we write all half equations in electrochemistry as reduction potentials.
- This means that we write each equation with the electrons on the left-hand side and show the species gaining electrons.
- We can do this because each reaction is reversible.

The direction of change

The direction of change

Every reduction potential will have a quoted value of E^θ.
- This is measured in volts.
- A positive E^θ means the reaction is favourable compared to the reduction of hydrogen ions.
- A negative E^θ means the reaction is not favourable compared to the reduction of hydrogen ions.

The Standard Hydrogen Electrode

The standard hydrogen electrode is used to measure reduction potentials.

The standard hydrogen electrode

The standard hydrogen electrode

The important features of the standard hydrogen electrode are:
- A pressure of H_2(g) at 100 kPa.
- An H⁺_(aq) concentration of 1 moldm^-3.
- A temperature of 298 K.

Why do we need it?

Why do we need it?

We can only measure an electrical potential if a current can run. We need one species to accept electrons and one to donate electrons.
- This means that we can never measure an electrode potential of a half-equation by itself.
We have to measure the electrode potential relative to the electrode potential of something else.
- We define the electrode potential of the standard hydrogen electrode to have E^θ = 0 V.
- Everything else is measured relative to this.

Standard electrode potentials

Standard electrode potentials

The θ in E^θ marks that the electrode potential is measured under standard conditions, which are:
- 298 K temperature.
- 100 kPa pressure.
- A concentration of 1 moldm^-3 for any solution.
It’s important to use standard conditions for a reference because changing any of these factors would change the potential and give you a different answer.

1

Physical Chemistry

1.1

Atoms, Molecules & Stoichiometry

1.1.1Relative Masses 1.1.2The Mole 1.1.3Mass Spectrometry 1.1.4Empirical & Molecular Formulae 1.1.5Balanced Equations 1.1.6Molar Volume 1.1.7End of Topic Test - Amount of Substance

1.2

Atomic Structure

1.2.1Fundamental Particles 1.2.2Isotopes & Mass Number 1.2.3Electron Shells, Sub-Shells & Orbitals 1.2.4Electron Configuration 1.2.5Ionisation Energy 1.2.6Factors Affecting Ionisation Energies 1.2.7Trends of Ionisation 1.2.8Specific Impacts on Ionisation Energies 1.2.9Electron Affinity 1.2.10End of Topic Test - Atomic Structure 1.2.11A-A* (AO2/3) - Atomic Structure

1.3

Chemical Bonding

1.3.1Ionic Bonding 1.3.2Covalent & Dative Bonding 1.3.3Shapes of Molecules 1.3.4Intermolecular Forces 1.3.5Intermolecular Forces 2 1.3.6Electronegativity 1.3.7Bond Length, Bond Energy, & Bond Polarity 1.3.8Metallic Bonding 1.3.9Physical Properties 1.3.10End of Topic Test - Bonding 1.3.11A-A* (AO2/3) - Bonding

1.4

States of Matter

1.4.1Simple Covalent Molecules 1.4.2The Ideal Gas Equation 1.4.3States of Matter 1.4.4Particle Diagrams 1.4.5The Liquid State 1.4.6Giant Ionic Lattices 1.4.7Giant Metallic Lattices 1.4.8Giant Covalent Structures 1.4.9Graphene & Fullerene 1.4.10Recycling

1.5

Chemical Energetics

1.5.1Calorimetry 1.5.2Bond Enthalpies 1.5.3Enthalpy Changes 1.5.4Hess' Law 1.5.5Born-Haber Cycles 1.5.6Born-Haber Cycle Calculations 1.5.7Entropy 1.5.8Free Energy 1.5.9End of Topic Test - Energetics

1.6

Electrochemistry

1.6.1Electrochemical Cells 1.6.2Electrochemical Series 1.6.3Commercial Application 1.6.4Nernst Equation 1.6.5Redox

1.7

Equilibria

1.7.1Dynamic Equilibrium & Le Chatelier 1.7.2Kc 1.7.3Kp 1.7.4pH 1.7.5The Ionic Product of Water 1.7.6Weak Acids & Bases 1.7.7Introduction to Solubility Equilibria 1.7.8Solubility Equilibria Calculations 1.7.9Free Energy of Dissolution 1.7.10pH and Solubility 1.7.11Common-Ion Effect 1.7.12End of Topic Test - Kp & Electrochemistry 1.7.13A-A* (AO2/3) - Electrochemical Cells

1.8

Partition Coefficient

1.9

Reaction Kinetics

1.9.1Collision Theory 1.9.2Orders, Rate Constants & Equations 1.9.3Rate Graphs 1.9.4Rate Determining Step 1.9.5Maxwell-Boltzmann Distribution 1.9.6Catalysts 1.9.7Homogeneous Catalysts 1.9.8Heterogeneous Catalysts 1.9.9End of Topic Test - Kinetics 1.9.10End of Topic Test - Rate Equations 1.9.11A-A* (AO2/3) - Rate Equations

2

Inorganic Chemistry

2.1

The Periodic Table

2.1.1The Periodic Table 2.1.2Trends in the Periodic Table 2.1.3End of Topic Test - Periodicity & Trends 2.1.4Ceramics 2.1.5Period 3 Elements & Oxides 2.1.6Period 3 Oxides 2.1.7End of Topic Test - Period 3

2.2

Group 2

2.2.1Group 2 Chemistry

2.3

Group 17

2.3.1Introduction to Halogens 2.3.2Reactions of Halogens 2.3.3Chlorine & Chlorate(I)2.3.4End of Topic Test - Group 17 2.3.5A-A* (AO2/3) - Periodicity, Group 2 & 17

2.4

Transition Metals

2.4.1General Properties 2.4.2Titrations 2.4.3Shapes of Complex Ions 2.4.4Variable Oxidation States 2.4.5Ligands 2.4.6Colours of Ions 2.4.7Stereoisomerism of Complex Ions 2.4.8Cisplatin 2.4.9Ligand Substitutions & Kstab 2.4.10End of Topic Test - Transition Metals 2.4.11A-A* (AO2/3) - Transition Metals

2.5

Nitrogen & Sulfur

2.5.1Nitrogen & Ammonia 2.5.2Formulated vs Manure Fertilisers 2.5.3Nitrogen Containing Fertilisers 2.5.4Fertilizers & Eutrophication 2.5.5Common Atmospheric Pollutants & Their Properties 2.5.6Catalytic Converters 2.5.7Atmospheric Oxides

3

Organic Chemistry & Analysis

3.1

Introduction to Organic Chemistry

3.1.1Naming Conventions 3.1.2Mechanism 3.1.3Isomerism 3.1.4End of Topic Test - Introduction to Organic Chem

3.2

Hydrocarbons

3.2.1Fractional Distillation 3.2.2Cracking 3.2.3Combustion 3.2.4Chlorination 3.2.5End of Topic Test - Alkanes 3.2.6Introduction to Alkenes 3.2.7Reactions of Alkenes 3.2.8Polymerisation Reactions 3.2.9End of Topic Test - Alkenes 3.2.10Arenes 3.2.11Evidence for Structure of Arenes 3.2.12Reactions of Benzene 3.2.13End of Topic Test -Arenes

3.3

Halogen Derivatives

3.3.1Properties of Haloalkanes 3.3.2Substitution Reactions of Haloalkanes 3.3.3Environmental Impacts of Haloalkanes 3.3.4End of Topic Test - Halogenoalkanes

3.4

Hydroxy Compounds

3.4.1Types of Alcohol 3.4.2Oxidation 1 3.4.3Oxidation 2 3.4.4Elimination 3.4.5Acids & Esters 3.4.6Acyl Chlorides & Acylation 3.4.7Phenols & Their Reactions 3.4.8End of Topic Test - Alcohols

3.5

Carbonyl Compounds

3.5.1Carbonyls 3.5.2Hydrogen Bonding & Carbonyls 3.5.3Aldehydes & Ketones 3.5.4Tri-Iodomethane Reaction 3.5.5End of Topic Test -Carbonyls

3.6

Carboxylic Acids & Derivatives

3.6.1Properties of Carboxylic Acids 3.6.2Esters 3.6.3Acyl Chlorides 3.6.4End of Topic Test - Carboxylic Acids

3.7

Nitrogen Compounds

3.7.1Nature & Preparation of Amines 3.7.2Basicity & Nucleophilicity 3.7.3Amides 3.7.4Reactions of Amino Acids 3.7.5Amino Acids

3.8

Polymerisation

3.8.1Properties of Addition Polymers 3.8.2Condensation Polymerisation 3.8.3Effects of Side-Chains on Polymers 3.8.4Hydrolysis of Ester & Amide Groups 3.8.5Proteins 3.8.6DNA 3.8.7Adhesive & Conducting Polymers 3.8.8End of Topic Test - Amines & Proteins

3.9

Analytical Techniques

3.9.1Chromatography 3.9.2High-Performance Liquid Chromatography 3.9.3Gas Chromatography 3.9.4IR Spectroscopy 3.9.5Uses of IR Spectroscopy 3.9.6Mass Spectrometry 3.9.7Mass Spectrometry Analysis 3.9.8Nuclear Magnetic Resonance 3.9.9Carbon-13 NMR 3.9.10Proton NMR I 3.9.11Proton NMR II 3.9.12End of Topic Test - Analytical Techniques 3.9.13A-A* (AO2/3) - Analytical Techniques

3.10

Organic Synthesis

3.10.1Chirality & Drug Synthesis 3.10.2Organic Synthesis 3.10.3Examples of Synthetic Routes 3.10.4End of Topic Test - Organic Synthesis

Jump to other topics

1

Physical Chemistry

1.1

Atoms, Molecules & Stoichiometry

1.1.1Relative Masses 1.1.2The Mole 1.1.3Mass Spectrometry 1.1.4Empirical & Molecular Formulae 1.1.5Balanced Equations 1.1.6Molar Volume 1.1.7End of Topic Test - Amount of Substance

1.2

Atomic Structure

1.2.1Fundamental Particles 1.2.2Isotopes & Mass Number 1.2.3Electron Shells, Sub-Shells & Orbitals 1.2.4Electron Configuration 1.2.5Ionisation Energy 1.2.6Factors Affecting Ionisation Energies 1.2.7Trends of Ionisation 1.2.8Specific Impacts on Ionisation Energies 1.2.9Electron Affinity 1.2.10End of Topic Test - Atomic Structure 1.2.11A-A* (AO2/3) - Atomic Structure

1.3

Chemical Bonding

1.3.1Ionic Bonding 1.3.2Covalent & Dative Bonding 1.3.3Shapes of Molecules 1.3.4Intermolecular Forces 1.3.5Intermolecular Forces 2 1.3.6Electronegativity 1.3.7Bond Length, Bond Energy, & Bond Polarity 1.3.8Metallic Bonding 1.3.9Physical Properties 1.3.10End of Topic Test - Bonding 1.3.11A-A* (AO2/3) - Bonding

1.4

States of Matter

1.4.1Simple Covalent Molecules 1.4.2The Ideal Gas Equation 1.4.3States of Matter 1.4.4Particle Diagrams 1.4.5The Liquid State 1.4.6Giant Ionic Lattices 1.4.7Giant Metallic Lattices 1.4.8Giant Covalent Structures 1.4.9Graphene & Fullerene 1.4.10Recycling

1.5

Chemical Energetics

1.5.1Calorimetry 1.5.2Bond Enthalpies 1.5.3Enthalpy Changes 1.5.4Hess' Law 1.5.5Born-Haber Cycles 1.5.6Born-Haber Cycle Calculations 1.5.7Entropy 1.5.8Free Energy 1.5.9End of Topic Test - Energetics

1.6

Electrochemistry

1.6.1Electrochemical Cells 1.6.2Electrochemical Series 1.6.3Commercial Application 1.6.4Nernst Equation 1.6.5Redox

1.7

Equilibria

1.7.1Dynamic Equilibrium & Le Chatelier 1.7.2Kc 1.7.3Kp 1.7.4pH 1.7.5The Ionic Product of Water 1.7.6Weak Acids & Bases 1.7.7Introduction to Solubility Equilibria 1.7.8Solubility Equilibria Calculations 1.7.9Free Energy of Dissolution 1.7.10pH and Solubility 1.7.11Common-Ion Effect 1.7.12End of Topic Test - Kp & Electrochemistry 1.7.13A-A* (AO2/3) - Electrochemical Cells

1.8

Partition Coefficient

1.9

Reaction Kinetics

1.9.1Collision Theory 1.9.2Orders, Rate Constants & Equations 1.9.3Rate Graphs 1.9.4Rate Determining Step 1.9.5Maxwell-Boltzmann Distribution 1.9.6Catalysts 1.9.7Homogeneous Catalysts 1.9.8Heterogeneous Catalysts 1.9.9End of Topic Test - Kinetics 1.9.10End of Topic Test - Rate Equations 1.9.11A-A* (AO2/3) - Rate Equations

2

Inorganic Chemistry

2.1

The Periodic Table

2.1.1The Periodic Table 2.1.2Trends in the Periodic Table 2.1.3End of Topic Test - Periodicity & Trends 2.1.4Ceramics 2.1.5Period 3 Elements & Oxides 2.1.6Period 3 Oxides 2.1.7End of Topic Test - Period 3

2.2

Group 2

2.2.1Group 2 Chemistry

2.3

Group 17

2.3.1Introduction to Halogens 2.3.2Reactions of Halogens 2.3.3Chlorine & Chlorate(I)2.3.4End of Topic Test - Group 17 2.3.5A-A* (AO2/3) - Periodicity, Group 2 & 17

2.4

Transition Metals

2.4.1General Properties 2.4.2Titrations 2.4.3Shapes of Complex Ions 2.4.4Variable Oxidation States 2.4.5Ligands 2.4.6Colours of Ions 2.4.7Stereoisomerism of Complex Ions 2.4.8Cisplatin 2.4.9Ligand Substitutions & Kstab 2.4.10End of Topic Test - Transition Metals 2.4.11A-A* (AO2/3) - Transition Metals

2.5

Nitrogen & Sulfur

2.5.1Nitrogen & Ammonia 2.5.2Formulated vs Manure Fertilisers 2.5.3Nitrogen Containing Fertilisers 2.5.4Fertilizers & Eutrophication 2.5.5Common Atmospheric Pollutants & Their Properties 2.5.6Catalytic Converters 2.5.7Atmospheric Oxides

3

Organic Chemistry & Analysis

3.1

Introduction to Organic Chemistry

3.1.1Naming Conventions 3.1.2Mechanism 3.1.3Isomerism 3.1.4End of Topic Test - Introduction to Organic Chem

3.2

Hydrocarbons

3.2.1Fractional Distillation 3.2.2Cracking 3.2.3Combustion 3.2.4Chlorination 3.2.5End of Topic Test - Alkanes 3.2.6Introduction to Alkenes 3.2.7Reactions of Alkenes 3.2.8Polymerisation Reactions 3.2.9End of Topic Test - Alkenes 3.2.10Arenes 3.2.11Evidence for Structure of Arenes 3.2.12Reactions of Benzene 3.2.13End of Topic Test -Arenes

3.3

Halogen Derivatives

3.3.1Properties of Haloalkanes 3.3.2Substitution Reactions of Haloalkanes 3.3.3Environmental Impacts of Haloalkanes 3.3.4End of Topic Test - Halogenoalkanes

3.4

Hydroxy Compounds

3.4.1Types of Alcohol 3.4.2Oxidation 1 3.4.3Oxidation 2 3.4.4Elimination 3.4.5Acids & Esters 3.4.6Acyl Chlorides & Acylation 3.4.7Phenols & Their Reactions 3.4.8End of Topic Test - Alcohols

3.5

Carbonyl Compounds

3.5.1Carbonyls 3.5.2Hydrogen Bonding & Carbonyls 3.5.3Aldehydes & Ketones 3.5.4Tri-Iodomethane Reaction 3.5.5End of Topic Test -Carbonyls

3.6

Carboxylic Acids & Derivatives

3.6.1Properties of Carboxylic Acids 3.6.2Esters 3.6.3Acyl Chlorides 3.6.4End of Topic Test - Carboxylic Acids

3.7

Nitrogen Compounds

3.7.1Nature & Preparation of Amines 3.7.2Basicity & Nucleophilicity 3.7.3Amides 3.7.4Reactions of Amino Acids 3.7.5Amino Acids

3.8

Polymerisation

3.8.1Properties of Addition Polymers 3.8.2Condensation Polymerisation 3.8.3Effects of Side-Chains on Polymers 3.8.4Hydrolysis of Ester & Amide Groups 3.8.5Proteins 3.8.6DNA 3.8.7Adhesive & Conducting Polymers 3.8.8End of Topic Test - Amines & Proteins

3.9

Analytical Techniques

3.9.1Chromatography 3.9.2High-Performance Liquid Chromatography 3.9.3Gas Chromatography 3.9.4IR Spectroscopy 3.9.5Uses of IR Spectroscopy 3.9.6Mass Spectrometry 3.9.7Mass Spectrometry Analysis 3.9.8Nuclear Magnetic Resonance 3.9.9Carbon-13 NMR 3.9.10Proton NMR I 3.9.11Proton NMR II 3.9.12End of Topic Test - Analytical Techniques 3.9.13A-A* (AO2/3) - Analytical Techniques

3.10

Organic Synthesis

3.10.1Chirality & Drug Synthesis 3.10.2Organic Synthesis 3.10.3Examples of Synthetic Routes 3.10.4End of Topic Test - Organic Synthesis

Practice questions on Electrochemical Cells

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1
When an electrode is used that is made from a metal that isn't involved in the redox reaction, what is it usually made from?Multiple choice
2
When an electrode is used that is made from a metal that isn't involved in the redox reaction, what is it usually made from?Multiple choice
3
The equation for the reduction and electron transfer of O<sub>2</sub> to 2O<sup>2-</sup> is:Multiple choice
4
We are able to change each half equation so that the electrons are on the left hand side because:Multiple choice
5
What are the important conditions in a standard hydrogen electrode?Fill in the list

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End of Topic Test - Energetics

Electrochemical Series