Chemical Effects of Electric Current
Focused last-minute revision notes with clear concepts, exam traps, key comparisons and compact practice.
Chapter Snapshot
- Some liquids conduct electricity because they contain mobile ions.
- Pure distilled water is a poor conductor, but dissolved salts, acids or bases increase conductivity.
- A tester can use an LED because small currents may not light a filament bulb.
- Electric current through a conducting liquid can cause gas bubbles, colour changes or metal deposition.
- These are chemical effects of electric current.
- Electroplating uses electric current to deposit a thin layer of one metal on another object.
- Chromium, nickel, silver, gold and tin coatings are used for protection or appearance.
- Electrical experiments with liquids must use safe low-voltage sources, never mains electricity.
What You Will Learn
- Identify conducting and poorly conducting liquids
- Explain why dissolved substances change conductivity
- Recognise chemical effects of current
- Explain electroplating
- Relate coatings to corrosion resistance and appearance
- Apply electrical safety
Last-Minute Chapter Map
Electric current through an electrolyte can transfer metal to an object during electroplating.
1. Do Liquids Conduct Electricity?
Some liquids conduct electric current while others conduct poorly. Tap water often conducts because it contains dissolved salts. Distilled water has very few ions and conducts poorly, but adding salt or acid increases conductivity.
2. Testing Conductivity
A simple tester contains a low-voltage cell, wires and a bulb or LED. An LED is useful because it can glow with much smaller current than a filament bulb. A magnetic compass near a wire can also indicate current through its magnetic effect.
3. Chemical Effects of Current
When current passes through a conducting solution, chemical changes may occur. Observations can include gas bubbles at electrodes, colour changes in solution or metal deposition on an electrode.
4. Electrodes and Electrolysis
Metal or carbon rods dipped into a conducting liquid are called electrodes. Chemical decomposition or reaction caused by electric current in a solution is broadly called electrolysis.
5. Electroplating
Electroplating uses electric current to deposit a thin layer of one metal on another object. It can improve appearance, reduce corrosion or provide a desirable surface property.
6. Uses of Electroplating
Chromium plating gives shiny corrosion-resistant surfaces to taps and bicycle parts. Tin coatings can protect iron food cans. Jewellery may be coated with gold or silver. The coating metal is chosen for the required property.
7. Safety
Use only cells or approved low-voltage school supplies. Never connect liquid experiments directly to household mains electricity. Electroplating chemicals should be handled under teacher supervision and disposed of responsibly.
Conductor Behaviour in Liquids
| Liquid | Typical Conductivity | Reason |
|---|---|---|
| Distilled water | Very low | Few dissolved ions |
| Salt solution | Higher | Mobile ions present |
| Tap water | Usually conducts | Contains dissolved minerals |
| Oil | Poor | Few charge carriers |
Exam Focus
Must Revise Before the Exam
- Conducting liquids
- Distilled vs tap water
- LED tester
- Chemical effects: bubbles/colour/deposition
- Electrodes
- Electrolysis
- Electroplating uses
- Safety
Common Mistakes
Key Terms
Key Terms
Quick Revision
Quick Revision
- Liquids conduct when mobile ions are available.
- Distilled water conducts poorly; salt solution conducts better.
- LED testers can detect small currents.
- Current can produce bubbles, colour change or metal deposition.
- Electrodes are conductors in contact with the solution.
- Electroplating deposits a thin metal coating.
- Use only safe low-voltage supplies.
Practice Questions
Which liquid is usually a poor conductor?
A. salt solution
B. tap water
C. distilled water
D. lemon juice
View Solution
Correct Answer: C. distilled water
Distilled water contains very few ions.
A thin metal coating deposited using electricity is produced by:
A. distillation
B. electroplating
C. filtration
D. combustion
View Solution
Correct Answer: B. electroplating
Electroplating deposits a metal layer using electric current.
Which can be a chemical effect of electric current?
A. gas bubbles
B. metal deposition
C. colour change
D. all of these
View Solution
Correct Answer: D. all of these
All can indicate chemical change in an electrolyte.
Why is an LED useful in a tester?
A. It needs very high current
B. It can glow with small current
C. It is a liquid
D. It prevents all current
View Solution
Correct Answer: B. It can glow with small current
An LED can indicate currents too small to heat a filament bulb visibly.
Why does salt solution conduct better than distilled water?
View Solution
Dissolved salt produces mobile ions that carry electric charge through the solution.
State two purposes of electroplating.
View Solution
It can protect a metal from corrosion and provide an attractive or useful surface, such as chromium plating or tin coating.
Why should electroplating not be done with household mains electricity?
View Solution
Liquids can conduct current and household mains voltage can cause severe electric shock. Only safe low-voltage sources are appropriate for school experiments.
Chapter Summary
Chapter Summary
- Liquids conduct when mobile ions are available.
- Distilled water conducts poorly; salt solution conducts better.
- LED testers can detect small currents.
- Current can produce bubbles, colour change or metal deposition.
- Electrodes are conductors in contact with the solution.
- Electroplating deposits a thin metal coating.
- Use only safe low-voltage supplies.