Electrolysis Examples

Test yourself

Electrolysis of Copper Sulfate

Copper can be purified using electrolysis. You need impure copper attached as the anode.

Copper sulfate electrolysis

The copper ions (Cu²⁺) will go into the electrolyte solution of copper sulfate.
The Cu²⁺ ions will be attracted to the cathode and pure copper will form.
- Cu²⁺_(aq) + 2e^- → Cu_(s)

Results

The impurities of the anode will fall to the bottom of the beaker.
When the mass of the cathode is constant, the purification process is complete.

Measure mass

To measure the mass of copper formed on the cathode over time:

Record the initial mass of the electrodes. The cathode must be cleaned for the copper to stick to it
Use a variable resistor because the current may vary during the process. It should be kept constant.

Measure mass (continued)

You should wash electrodes to remove any copper sulfate. You should then dry them.
You should also wash the electrodes with a more volatile solvent to make them dry faster. You could use propanone, for instance.

Equation

Measure the final mass of the electrodes to work out the change in mass: change in mass = final mass - initial mass.

Electrolysis Examples

You need to be able to describe the electrode products and the observations made during the electrolysis of:

Molten lead(II) bromide

When we use graphite electrodes to apply electricity across molten lead bromide, we form lead (metal) at the cathode and bromine (non-metal) at the anode.
- Lead bromide → lead + bromine
We know lead is present if a shiny metal forms around the cathode.
Bromine is observed as a brown gas because of the high temperatures reached in the process.

Concentrated hydrochloric acid

Applying electricity across hydrochloric acid with graphite electrodes produces hydrogen gas at the cathode and chlorine gas (non-metal) at the anode.
We can detect hydrogen at the cathode using a lit splint. A squeaky pop is heard.
We can detect chlorine gas by its smell. It also bleaches litmus paper.

Concentrated aqueous sodium chloride

The electrolysis of aqueous solutions is a little more complex, as you have to consider the water.
In the case of aqueous sodium chloride, hydrogen is formed instead of sodium.
Applying electricity across aqueous sodium chloride produces hydrogen gas at the cathode and chlorine gas (non-metal) at the anode.
The electrodes are inert graphite or platinum.
The formation of hydrogen at the cathode can be detected using a lit split. A squeaky pop is heard.
The chlorine gas can be detected by its smell. It also bleaches litmus paper.

Dilute sulfuric acid

When dilute sulfuric acid is electrolysed, hydrogen is produced from the acid and oxygen from the water.
Applying electricity to sulfuric acid with graphite electrodes produces hydrogen gas at the cathode and oxygen at the anode.
The formation of hydrogen at the cathode can be detected using a lit split. A squeaky pop is heard.
The oxygen gas produced at the anode can also be detected using a glowing splint. The splint will relight in oxygen gas.

During electrolysis, different reactions take place at the different electrodes. Half equations show the reactions that happen at each electrode. The electrolysis of lead bromide is an example of this:

At the anode (positive electrode)

Oxidation reactions happen i.e. negatively charged ions lose electrons.
- E.g. 2Br^- → Br₂ + 2e^-

At the cathode (negative electrode)

Reduction reactions happen i.e. positively charged ions gain electrons.
- E.g. Pb²⁺ + 2e^- → Pb

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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