Chemical Effects of Electric Current

Testing Conductivity of Liquids

Why is it Dangerous to Touch Electrical Appliances with Wet Hands?

• Wet Hands Warning: Touching electrical appliances with wet hands is dangerous.
• Good vs. Poor Conductors:
  • Good conductors: Allow electricity to pass (e.g., copper, aluminum).
  • Poor conductors: Do not allow electricity to pass easily (e.g., rubber, plastic, wood).

Testing Conductivity of Liquids

• Use Electric Cells Only: Do not use mains electricity.

Do Liquids Conduct Electricity?

• Same Tester, Different Use: Use the tester made earlier but replace the cell with a battery.
• Checking the Tester:
  • Join the tester ends briefly. If the bulb glows, it’s working.
  • If the bulb doesn’t glow:
    • Check for loose connections.
    • Replace the bulb if fused.
    • Replace the cells if used up.

Why the Bulb May Not Glow Even if the Liquid Conducts

• Weak Current: The current might be too weak to heat the bulb filament.
• Conductivity: Some materials conduct electricity weakly compared to metals.

Detecting Weak Currents

• Magnetic Effect: Use a compass to detect weak currents.

Making a Tester Using Magnetic Effect

1. Prepare: Wrap wire around a matchbox tray and place a compass inside.
2. Connect: Attach wire ends to a battery.
3. Test Liquids: Dip ends into various liquids and observe compass deflection.

Liquids to Test

• Lemon juice
• Vinegar
• Tap water
• Vegetable oil
• Milk
• Honey

Observations

• Good Conductors: Some liquids are good conductors.
• Poor Conductors: Others are poor conductors.

Special Cases: Air and Distilled Water

• Air: Usually a poor conductor but can conduct electricity during lightning.
• Distilled Water: Does not conduct electricity unless salt is added.

Testing Distilled Water

1. Test Distilled Water: Use the tester.
2. Add Salt: Dissolve salt in distilled water and test again.
3. Conclusion: Distilled water with salt conducts electricity.

Testing Other Solutions

• Common Conductors: Solutions of acids, bases, and salts conduct electricity.

Chemical Effects of Electric Current

Introduction

• Electric current has various effects.
• When current flows through a conducting solution, it produces chemical changes.

Chemical Effects of Electric Current

• Passage of electric current causes chemical reactions.
• Possible Reactions:
  • Formation of gas bubbles.
  • Metal deposits on electrodes.
  • Color change in the solution.
• Depends on: Type of solution and electrodes.

Historical Note

• William Nicholson (1800):
  • Demonstrated electrolysis of water.
  • Produced oxygen and hydrogen gas bubbles.

Example: Potato Experiment

• Boojho’s Experiment:
  • Tested if fruits/vegetables conduct electricity using a potato.
  • Inserted tester wires into potato halves.
  • Observed greenish blue spot around the positive terminal wire.

Unexpected Discovery

• Observation:
  • Greenish blue spot always around positive terminal wire.
• Conclusion:
  • Current caused a chemical effect in the potato.
  • Useful for identifying the positive terminal of a cell or battery.

Scientific Process

• Sometimes, while searching for one thing, you discover something else.
• Many important discoveries are made unexpectedly.

Electroplating

• Shiny bicycle handlebars and wheel rims get scratched, revealing the metal underneath.
• Some jewelry appears gold but wears off to show a different metal beneath.
• This is due to a metal coating another metal.

How Electroplating Works

• Electric current in copper sulphate solution splits copper sulphate into copper and sulphate.
• Copper ions move to the negative electrode and deposit there.
• Copper from the positive electrode dissolves, balancing the solution.

Definition

• Electroplating: Depositing a layer of one metal on another using electricity.

Applications

• Chromium Plating:
  • Used on car parts, bath taps, kitchen burners, bike handlebars.
  • Chromium is shiny, resists corrosion and scratches, but is expensive.
  • Coating cheaper metals with chromium saves costs.
• Jewelry:
  • Silver and gold electroplated on less expensive metals.
  • Makes affordable jewelry with a gold/silver appearance.
• Tin Cans:
  • Tin plated on iron to prevent food from contacting reactive iron.
• Iron Protection:
  • Zinc coating on iron used in bridges and cars to prevent rust and corrosion.

Environmental Note

• Disposal of used conducting solutions in electroplating factories is a concern due to pollution.
• Specific guidelines exist for safe disposal to protect the environment.

Chapter Summary:

• Some liquids conduct electricity well, while others don’t conduct well.
• Liquids like acids, bases, and salts usually conduct electricity.
• When electricity passes through a conducting liquid, it causes chemical changes.
• These changes are called the chemical effects of currents.
• Electroplating is a process where a layer of metal is deposited onto another material using electricity.

KEYWORDS

1. ELECTRODE
2. ELECTROPLATING
3. GOOD CONDUCTOR
4. LED
5. POOR CONDUCTOR