Applications of Electrochemistry and Bioelectricity
1. Electroplating
Learning outcomes
- I can explain the purpose of electroplating.
- I can describe how electroplating uses electrolysis.
- I can identify the roles of the anode, cathode, and electrolyte.
- I can explain how electroplating improves material properties.
- I can evaluate applications of electroplating in industry.
What Is Electroplating?
Electroplating is the process of using electricity to deposit a thin layer of one metal onto the surface of another object.
It is a practical application of:
During electroplating, metal ions in an electrolyte gain electrons and form solid metal on the surface of the object being coated.
In simple terms:
metal ions in solution → solid metal coating
Electroplating is widely used to:
- improve appearance
- prevent corrosion
- increase resistance to wear
- improve electrical conductivity
- reduce friction
- improve surface hardness
- produce specialized surface properties
The Basic Electroplating Cell
A typical electroplating system contains:
- a DC power supply
- an anode
- a cathode
- an electrolyte
- the object being plated
- ions of the coating metal
The object that will receive the coating is connected as the:
cathode.
The metal being deposited is present as:
positive metal ions in the electrolyte.
In many systems, the anode is made from the same metal that is being deposited.
The Cathode
The object being electroplated is normally the:
cathode.
During electrolysis, the cathode is connected to the:
negative terminal.
Positive metal ions are attracted toward it.
At the cathode, the metal ions:
gain electrons.
Remember:
Reduction = gain of electrons
and:
Reduction occurs at the cathode.
Metal Deposition at the Cathode
Suppose an object is being plated with copper.
The electrolyte contains:
Cu²⁺ ions.
The Cu²⁺ ions move toward the cathode and gain electrons:
Cu²⁺ + 2e⁻ → Cu
The copper ions become neutral copper atoms.
These atoms form a layer of:
solid copper
on the object's surface.
Why Is the Object the Cathode?
Metal ions are:
positively charged.
To form metal atoms, they must:
gain electrons.
Electrons are supplied at the cathode.
Therefore:
Metal ions → cathode → gain electrons → metal coating
This is why the object being electroplated must normally be connected as the:
cathode.
The Anode
The other electrode is the:
anode.
During electrolysis, the anode is connected to the:
positive terminal.
Oxidation occurs at the anode.
Remember:
AnOx
ANode = OXidation
In many electroplating systems, the anode is made from the metal being:
deposited.
A Reactive Metal Anode
Suppose copper is being used to coat an object.
A copper anode can be used.
At the anode:
Cu → Cu²⁺ + 2e⁻
Copper atoms lose electrons and enter the electrolyte as:
Cu²⁺ ions.
The copper anode gradually:
loses mass.
What Happens at Both Electrodes?
In copper electroplating:
At the anode:
Cu → Cu²⁺ + 2e⁻
At the cathode:
Cu²⁺ + 2e⁻ → Cu
Copper leaves the anode and copper is deposited onto the:
cathode.
In an idealized system, copper is effectively transferred from:
anode → electrolyte → cathode.
The Electrolyte
The electrolyte contains mobile ions and allows electrical charge to move through the solution.
For copper electroplating, the electrolyte must provide:
Cu²⁺ ions.
A suitable copper-containing solution might contain a dissolved copper salt.
The electrolyte has two important functions:
- allows ions to move through the cell
- supplies metal ions for deposition
The Three Main Components
A simple way to remember an electroplating setup is:
Cathode → object being coated
Electrolyte → contains ions of coating metal
Anode → often made from coating metal
For example, copper plating:
Cathode → object
Electrolyte → contains Cu²⁺
Anode → copper
Ion and Electron Movement
During electroplating, metal ions move through the:
electrolyte.
Electrons move through the:
external electrical circuit.
These are different types of charge movement.
For copper plating:
Cu²⁺ ions → toward cathode
At the cathode:
Cu²⁺ + 2e⁻ → Cu
The metal becomes part of the object's:
surface coating.
Example: Copper Plating
Suppose we want to coat a steel object with copper.
The steel object becomes the:
cathode.
A copper electrode can become the:
anode.
The electrolyte contains:
Cu²⁺ ions.
At the cathode:
Cu²⁺ + 2e⁻ → Cu
Copper forms on the steel.
At the anode:
Cu → Cu²⁺ + 2e⁻
Copper enters the electrolyte.
Over time:
cathode mass increases
and:
anode mass decreases.
Example: Silver Plating
Silver plating uses the same basic principle.
Silver ions move toward the cathode.
At the cathode:
Ag⁺ + e⁻ → Ag
Silver metal is deposited onto the object.
Silver plating can be used for:
- decorative objects
- jewelry
- electrical components
- specialized industrial surfaces
The exact electrolytes used industrially are carefully selected for safety and coating quality.
Example: Nickel Plating
Nickel can also be deposited electrochemically.
At the cathode:
Ni²⁺ + 2e⁻ → Ni
Nickel coatings can provide:
- corrosion resistance
- wear resistance
- improved appearance
- a suitable surface for further coatings
Nickel plating is widely used in:
manufacturing and engineering.
Example: Chromium Plating
Chromium-based coatings are used on many manufactured components.
They can provide:
- a shiny appearance
- increased surface hardness
- improved wear resistance
- improved corrosion resistance
Chromium coatings can be decorative or:
functional.
Industrial chromium-plating chemistry requires careful environmental and safety controls because some chromium compounds used in traditional processes are:
hazardous.
Decorative Electroplating
Sometimes the main purpose of electroplating is:
appearance.
A cheaper material can be covered with a thin layer of a more attractive metal.
Examples include:
- gold-plated jewelry
- silver-plated objects
- decorative nickel coatings
- chromium-finished components
Only a thin layer of the expensive metal may be required.
This can make the product:
less expensive than making it entirely from that metal.
Corrosion Protection
Electroplating can protect an underlying material from:
corrosion.
The coating creates a barrier between the base material and substances in the environment such as:
- water
- oxygen
- salts
- chemicals
If the coating remains intact, it can reduce the exposure of the underlying metal to:
corrosive conditions.
What Is Corrosion?
Corrosion is the gradual deterioration of a material through chemical or electrochemical reactions with its environment.
Rusting of iron is a familiar example.
Iron reacts in the presence of oxygen and water to eventually form hydrated iron oxides commonly called:
rust.
A suitable protective coating can reduce contact between iron and its environment.
Electroplating and Wear Resistance
Machine parts may experience:
- rubbing
- scratching
- abrasion
- repeated contact
A suitable electroplated coating can make the surface more resistant to:
wear.
This can increase the useful lifetime of a component.
Surface Hardness
The interior of a component and its surface do not always need the same properties.
A manufacturer may want:
a tough, inexpensive core
but:
a hard, wear-resistant surface.
Electroplating can sometimes provide this combination by changing the properties of the:
surface.
Electrical Conductivity
Electroplating is extremely important in:
electronics.
A component may be coated with a metal that provides:
- good electrical conductivity
- reliable electrical contact
- corrosion resistance
- reduced contact resistance
Metals such as:
gold, silver, copper, nickel, and tin
are used in different electronic applications.
Gold-Plated Electrical Contacts
Gold is an excellent material for some electrical contacts because it:
- conducts electricity
- resists oxidation
- provides reliable contact surfaces
However, gold is:
expensive.
Instead of making an entire connector from gold, manufacturers can apply a very thin gold coating to the:
important contact surface.
Electroplating Can Save Material
One important advantage of electroplating is that the whole object does not need to be made from the coating material.
For example, an object can have:
inexpensive structural material inside
and:
specialized metal coating outside.
This can reduce the amount of expensive or scarce material required.
Preparing the Surface
Successful electroplating requires a:
clean surface.
Dirt, grease, oxide layers, and other contamination can prevent the metal coating from attaching properly.
Industrial preparation may involve:
- cleaning
- degreasing
- rinsing
- surface activation
- removal of oxide layers
Poor surface preparation can produce a coating that is:
- uneven
- weakly attached
- rough
- patchy
Why Surface Preparation Matters
Imagine trying to paint a surface covered in:
oil and dirt.
The paint would not attach properly.
Electroplating has a similar problem.
The deposited metal must form good contact with the:
underlying surface.
Proper cleaning is therefore a critical part of the electroplating process.
Current and Coating Rate
The amount of metal deposited depends partly on the amount of electrical charge passing through the cell.
Greater current means more charge passes per second.
Under suitable conditions, increasing the current can increase the:
rate of metal deposition.
However, simply using a very large current does not necessarily produce a better coating.
Current Density
An important industrial quantity is:
current density.
Current density describes the current passing through a particular electrode area.
If current density is too high, the coating may become:
- rough
- uneven
- poorly attached
- less desirable
Manufacturers therefore carefully control:
electrical conditions.
Time and Coating Thickness
Electroplating for a longer time generally allows more metal to be:
deposited.
Therefore coating thickness can be controlled partly by adjusting:
- current
- plating time
- surface area
This makes electroplating useful when a specific coating thickness is required.
Faraday's Laws and Electroplating
The amount of material deposited during electrolysis is related to the quantity of:
electric charge transferred.
Electric charge can be calculated using:
Q = It
where:
Q = charge in coulombs (C)
I = current in amperes (A)
t = time in seconds (s)
This provides a quantitative connection between electricity and the amount of:
metal deposited.
Worked Example: Calculating Charge
An electroplating cell operates at:
2.0 A
for:
10 minutes.
First convert the time:
10 min × 60 = 600 s
Use:
Q = It
Q = 2.0 × 600
Q = 1200 C
Therefore:
1200 C of charge
passes through the circuit.
Factors Affecting Electroplating Quality
Several factors affect the quality of a plated surface:
- current density
- plating time
- ion concentration
- temperature
- electrode spacing
- surface cleanliness
- electrolyte composition
- movement of the electrolyte
Industrial electroplating requires careful control of these variables to produce:
consistent coatings.
Uneven Coatings
Electric fields are not always distributed evenly around an object.
Edges and projections may experience different current densities from flat or recessed areas.
As a result, metal may deposit:
unevenly.
Manufacturers can adjust:
- electrode shape
- electrode position
- current
- solution movement
to improve coating uniformity.
Electroplating in the Automotive Industry
Electroplating is used extensively in:
vehicles.
Applications can include:
- decorative trim
- fasteners
- electrical connectors
- engine components
- wear-resistant parts
- corrosion-resistant surfaces
Different coatings are selected according to the required:
properties.
Electroplating in Electronics
Electronic equipment contains many electroplated components.
Applications include:
- connectors
- switches
- contacts
- circuit-board features
- semiconductor manufacturing components
Electroplating can provide extremely thin and precisely controlled:
metal layers.
Electroplating in Jewelry
Jewelry is one of the most familiar applications.
A less expensive metal can be coated with:
- gold
- silver
- rhodium
- other decorative metals
This can provide the desired:
appearance and surface properties
while reducing the amount of expensive metal required.
Electroplating in Aerospace
Aircraft and spacecraft components may require surfaces with carefully controlled properties.
Electroplated coatings can be used for:
- corrosion protection
- wear resistance
- electrical performance
- specialized engineering surfaces
In these applications, coating thickness and quality must be:
carefully controlled.
Electroplating in Manufacturing
Electroplating can be used on:
- tools
- machine components
- fasteners
- bearings
- molds
- electrical equipment
- decorative products
The purpose depends on the application.
The same underlying electrochemical process can create surfaces with very different:
properties.
Advantages of Electroplating
Electroplating can provide several advantages.
It can:
- improve appearance
- protect against corrosion
- increase wear resistance
- improve electrical properties
- modify surface hardness
- reduce the amount of expensive metal required
- extend product lifetime
- restore dimensions on some worn components
Limitations of Electroplating
Electroplating also has disadvantages.
These can include:
- energy consumption
- chemical waste
- wastewater treatment requirements
- potentially hazardous chemicals
- equipment costs
- difficulty coating complex shapes uniformly
- coating failure if surfaces are poorly prepared
Therefore electroplating must be evaluated based on both:
benefits and costs.
Environmental Considerations
Some electroplating processes use solutions containing metal ions or other chemicals that can be harmful if released into the:
environment.
Wastewater may require treatment to remove:
- metal ions
- acids
- alkalis
- other processing chemicals
Modern facilities must carefully manage:
chemical waste and wastewater.
Worker Safety
Industrial electroplating may involve:
- corrosive solutions
- toxic substances
- electrical equipment
- gases
- heated solutions
Proper industrial systems therefore require:
- ventilation
- protective equipment
- chemical handling procedures
- wastewater controls
- monitoring
These measures help reduce risks to workers and the:
environment.
Electroplating vs Painting
Both electroplating and painting can modify an object's surface.
However:
Painting
adds a layer of paint or polymer.
Electroplating
deposits a layer of metal using electrolysis.
Electroplating can therefore provide metallic properties such as:
- electrical conductivity
- metallic appearance
- wear resistance
- specialized corrosion resistance
that ordinary paint may not provide.
Electroplating vs Galvanizing
These processes should not be confused.
Electroplating
uses electrolysis to deposit a metal coating.
Galvanizing
commonly refers to coating iron or steel with zinc, often by dipping it into molten zinc.
Zinc provides additional protection because it is more reactive than iron and can act as a:
sacrificial metal.
Electroplating can also be used to apply zinc, but not all galvanizing is performed by electrolysis.
Electroplating vs Electrorefining
Both processes use electrolysis, but they have different purposes.
Electroplating
Purpose:
coat an object with metal.
Electrorefining
Purpose:
purify a metal.
In copper electrorefining, copper moves from an impure anode to a pure:
cathode.
Evaluating an Electroplating Application
When evaluating whether electroplating is suitable, ask:
What property needs improvement?
For example:
- appearance?
- corrosion resistance?
- conductivity?
- hardness?
- wear resistance?
Then consider:
What metal provides that property?
Finally consider:
- cost
- durability
- environmental impact
- safety
- coating thickness
- maintenance
- alternatives
This allows an evidence-based evaluation rather than simply deciding that electroplating is always:
better.
Worked Example 1
A steel key is being copper plated.
Which electrode should the key be?
The key needs to receive copper atoms.
Copper ions must gain electrons:
Cu²⁺ + 2e⁻ → Cu
Reduction occurs at the cathode.
Therefore:
the key must be the cathode.
Worked Example 2
What could be used as the anode during copper plating?
A:
copper electrode.
At the anode:
Cu → Cu²⁺ + 2e⁻
This supplies additional Cu²⁺ ions to the electrolyte.
Worked Example 3
What must the electrolyte contain during copper plating?
It must contain:
Cu²⁺ ions.
These ions move toward the cathode and are reduced:
Cu²⁺ + 2e⁻ → Cu.
Worked Example 4
Why does the cathode gain mass?
Metal ions from the electrolyte are converted into:
solid metal atoms.
These atoms remain on the object's surface.
Therefore the object's:
mass increases.
Worked Example 5
Why can a reactive anode lose mass?
Metal atoms from the anode can lose electrons.
For copper:
Cu → Cu²⁺ + 2e⁻
The atoms leave the solid electrode and enter the:
solution.
Worked Example 6
Why might an electrical connector be gold plated rather than made entirely from gold?
Gold has useful surface properties, including:
high corrosion resistance and good electrical conductivity.
However, it is expensive.
A thin coating can provide useful surface properties while using much less:
gold.
Worked Example 7
A plated object has a patchy coating.
Give two possible causes.
Possible causes include:
- poor surface cleaning
- uneven current density
- unsuitable electrode positioning
- incorrect current
- unsuitable electrolyte concentration
Any of these can affect the:
quality of deposition.
Worked Example 8
An electroplating cell operates at 3.0 A for 5 minutes.
Calculate the charge transferred.
Convert time:
5 × 60 = 300 s
Use:
Q = It
Q = 3.0 × 300
Q = 900 C
Therefore:
900 C
of charge passes through the circuit.
Worked Example 9
Why might electroplating extend the life of a machine component?
A suitable coating can improve:
wear resistance or corrosion resistance.
This reduces damage to the underlying material and may allow the component to remain useful:
for longer.
Worked Example 10
Why must electroplating waste be treated carefully?
Waste solutions may contain:
metal ions and other potentially harmful chemicals.
If released untreated, these substances could contaminate:
water and soil.
Appropriate treatment reduces environmental impact.
Common Mistake: The Object Is the Anode
The object being plated must receive metal.
Metal ions gain electrons at the:
cathode.
Therefore:
object being plated = cathode.
Common Mistake: The Metal Coating Comes Directly Through the Wire
Metal does not travel through the wire.
Electrons travel through the:
external circuit.
Metal ions move through the:
electrolyte.
The ions gain electrons at the cathode and become solid metal.
Common Mistake: The Anode Always Has to Be the Coating Metal
A soluble anode made from the coating metal is common in many electroplating systems.
However, some industrial processes use:
inert or dimensionally stable anodes.
The metal ions are then supplied and maintained through the electrolyte chemistry.
Common Mistake: Electroplating Changes the Entire Object
Electroplating mainly modifies the:
surface.
The object's interior usually remains made from the original material.
This is one of the major advantages of the process.
Common Mistake: A Thicker Coating Is Always Better
A thicker coating uses more:
material, time, and energy.
The ideal thickness depends on the required performance.
Manufacturers aim for a coating that provides the necessary properties without unnecessary:
cost and material use.
Check Your Understanding
- Define electroplating.
- What chemical process is used in electroplating?
- What is the purpose of the cathode?
- What is the purpose of the anode?
- What is the purpose of the electrolyte?
- Which electrode is the object being plated?
- Why must the object be the cathode?
- What type of reaction occurs at the cathode?
- What type of reaction occurs at the anode?
- What happens to metal ions at the cathode?
- Write the half-equation for copper deposition.
- Write the half-equation for silver deposition.
- Write the half-equation for nickel deposition.
- What happens to a copper anode during copper electroplating?
- Write the half-equation for a copper anode.
- Why does a copper anode lose mass?
- Why does the cathode gain mass?
- What must a copper-plating electrolyte contain?
- Describe the movement of Cu²⁺ ions during electroplating.
- Where do electrons move in an electroplating system?
- Explain how copper can effectively be transferred from anode to cathode.
- Why must an object be cleaned before electroplating?
- What might happen if grease remains on the surface?
- Give three reasons why manufacturers electroplate products.
- How can electroplating reduce corrosion?
- How can electroplating increase wear resistance?
- How can electroplating improve electrical components?
- Why are some electrical contacts gold plated?
- Why not make the entire component from gold?
- Give two uses of nickel plating.
- Give two uses of decorative electroplating.
- How can electroplating change surface hardness?
- Explain why electroplating can reduce material costs.
- What is current density?
- How can current affect the rate of deposition?
- How can plating time affect coating thickness?
- State the equation relating charge, current, and time.
- Calculate the charge transferred by a 2 A current operating for 300 s.
- Name three factors affecting coating quality.
- Why might complex objects develop uneven coatings?
- Give two environmental concerns associated with electroplating.
- Why must electroplating wastewater be treated?
- Compare electroplating and painting.
- Compare electroplating and galvanizing.
- Compare electroplating and electrorefining.
- Explain how electroplating is used in electronics.
- Explain how electroplating is used in jewelry.
- Explain one application of electroplating in the automotive industry.
- Give one advantage and one limitation of electroplating.
- Describe the complete process of electroplating an object with copper.
Key Terms
Electroplating: Use of electrolysis to deposit a thin metal coating onto an object.
Cathode: Electrode where reduction occurs; normally the object being electroplated.
Anode: Electrode where oxidation occurs.
Electrolyte: Conducting liquid containing mobile ions required for electroplating.
Reduction: Gain of electrons.
Oxidation: Loss of electrons.
Metal deposition: Formation of solid metal from metal ions at an electrode.
Coating: Thin layer of material covering another material.
Corrosion: Gradual deterioration of a material through chemical or electrochemical reactions with its environment.
Current density: Electrical current per unit electrode area.
Electrorefining: Use of electrolysis to purify a metal.
Galvanizing: Application of a zinc coating to iron or steel, commonly by hot-dip treatment.
Key Takeaways
- Electroplating uses electrolysis to deposit a thin layer of metal onto an object.
- The object being plated is normally the cathode.
- Metal ions move through the electrolyte toward the cathode.
- At the cathode, metal ions gain electrons and form solid metal.
- Reduction always occurs at the cathode.
- In many systems, the anode is made from the coating metal.
- A reactive metal anode can dissolve and replace metal ions in the electrolyte.
- During copper plating, Cu²⁺ + 2e⁻ → Cu occurs at the cathode.
- Electroplating can improve appearance, corrosion resistance, wear resistance, hardness, and electrical properties.
- Thin coatings allow expensive materials to be used only where their surface properties are needed.
- Surface preparation is essential for a strong and uniform coating.
- Current, time, temperature, concentration, and current density can affect coating quality.
- Electroplating is widely used in electronics, jewelry, automotive manufacturing, aerospace, and engineering.
- Electroplating can generate chemical waste and therefore requires careful environmental and safety management.
- Choosing an electroplating process requires balancing the desired surface properties against cost, durability, safety, and environmental impact.