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Chemical Effects of Electric Current — Question 3

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Question 3

Name three liquids, which when tested in the manner shown in Fig.11.9, may cause the magnetic needle to deflect.

Sketch the larynx and explain its function in your own words. NCERT Class 8 Science CBSE Solutions.
Answer
  1. Saltwater
  2. Lemon juice
  3. Vinegar

Source: This question is from Chemical Effects of Electric Current, Science — Class 8, CBSE Board.

Key Concepts Covered

This question tests your understanding of the following concepts from the chapter Chemical Effects of Electric Current: Question, Liquids, Tested, Manner, Shown, Fig. These are fundamental topics in Science that students are expected to master as part of the CBSE Class 8 curriculum.

A thorough understanding of these concepts will help you answer similar questions confidently in your CBSE examinations. These topics are frequently tested in both objective and subjective sections of Science papers. We recommend revising the relevant section of your textbook alongside practising these solved examples to build a strong foundation.

How to Approach This Question

Read the question carefully and identify what is being asked. Break down complex questions into smaller parts. Use the terminology and concepts discussed in this chapter. Structure your answer logically — begin with a definition or key statement, then provide supporting details. Review your answer to ensure it addresses all parts of the question completely.

Key Points to Remember

  • Read the question carefully and identify all parts before answering.
  • Use the terminology specific to this subject and chapter.
  • Review the textbook content for this chapter before attempting questions.
  • Practice writing concise, well-structured answers within time limits.

Related Questions from Chemical Effects of Electric Current

Practice more questions from Chemical Effects of Electric Current — Science, Class 8 CBSE

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

ConceptDetails
Electrolysis of Water2H2O → 2H2 + O2 (hydrogen at cathode, oxygen at anode)
Electroplating SetupCathode: object to plate; Anode: plating metal; Electrolyte: plating metal's salt solution
PANIC RulePositive Anode, Negative Is Cathode
Conduction in LiquidsRequires 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 MetalUsed OnReason
ChromiumCar parts, taps, cycle handlesShiny appearance, corrosion resistance
Gold/SilverJewelleryAttractive look at lower cost
TinFood cansNon-toxic, prevents iron rusting
ZincIron pipes, bridges, fencesPrevents rusting (galvanising)
NickelCoins, utensilsDurability, 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.