Chemical Effects of Electric Current — Question 2
Back to all questionsQuestion 2
When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?
The deflection of the magnetic needle can be explained by the flow of current through the wounded wire of the tester. When the free ends of a tester are dipped into a solution, the circuit becomes complete and current starts flowing through the solution proving that the solution is a good conductor of electricity. The current then flows through the wire creating a magnetic field that deflects the magnetic needle.
Chapter Overview: Chemical Effects of Electric Current
This chapter explores how electric current affects liquids: which liquids conduct (electrolytes with ions) and which do not, the chemical effects observed (metal deposition, gas bubbles, colour change), and the practical applications of electrolysis and electroplating.
Board Exam Weightage: 4-6 marks | Difficulty: Moderate
Key Formulas & Concepts
| Concept | Details |
|---|---|
| Electrolysis of Water | 2H2O → 2H2 + O2 (hydrogen at cathode, oxygen at anode) |
| Electroplating Setup | Cathode: object to plate; Anode: plating metal; Electrolyte: plating metal's salt solution |
| PANIC Rule | Positive Anode, Negative Is Cathode |
| Conduction in Liquids | Requires free ions (dissolved salts, acids, bases) |
Must-Know Concepts
- Liquids with ions (salt solution, acids, bases) conduct electricity; pure water does not
- Chemical effects of current in liquids: metal deposition, gas evolution, colour change
- In electrolysis of water, hydrogen collects at cathode (double volume) and oxygen at anode
- Electroplating deposits a thin layer of desired metal on another object
- Chromium plating for shine and corrosion resistance; tin plating for food safety; zinc coating (galvanising) for rust prevention
- LED tester is more sensitive than a bulb for testing liquid conductivity
Electroplating Applications
| Plating Metal | Used On | Reason |
|---|---|---|
| Chromium | Car parts, taps, cycle handles | Shiny appearance, corrosion resistance |
| Gold/Silver | Jewellery | Attractive look at lower cost |
| Tin | Food cans | Non-toxic, prevents iron rusting |
| Zinc | Iron pipes, bridges, fences | Prevents rusting (galvanising) |
| Nickel | Coins, utensils | Durability, corrosion resistance |
Common Mistakes to Avoid
- Thinking pure/distilled water conducts electricity (it does not, no ions)
- Confusing anode (positive) and cathode (negative)
- Thinking electroplating changes the entire material (only a thin surface layer)
- Forgetting that electrolyte must be a salt of the plating metal
Scoring Tips
- Use PANIC to remember: Positive Anode, Negative Is Cathode
- Draw the electroplating setup with clear labels
- Test 5 household liquids mentally: which conduct and why
- Remember the 3 chemical effects: deposition, gas bubbles, colour change
Frequently Asked Questions
Q: How many marks does this chapter carry in the exam?
A: Approximately 4-6 marks in the annual exam.
Q: What question types are commonly asked?
A: MCQs (1 mark), Very Short Answer (2 marks), Short Answer (3 marks), and Long Answer / Diagram (5 marks).
Q: Is this chapter important for competitive exams?
A: Yes, concepts from this chapter appear in NTSE, Olympiad, and other science competitions.