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Important Questions: CBSE Class 8 Science Chapter 11 Chemical Effects of Electric Current

Chemical Effects of Electric Current is a high-scoring chapter in CBSE Class 8 Science, blending concept clarity with practical applications like electroplating and water testing. Questions range from simple MCQs on conductors to detailed case studies on industrial electrolysis. This page organises 18 curated questions by marks weightage, each with model answers that mirror CBSE evaluation criteria, so students can practise smarter and parents can guide revision at home.

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Key takeaways

✓Chapter 11 carries 4–6 marks in CBSE Class 8 Science exams, often split into MCQs, short answers and one long or case-based question.
✓NCERT terms—conductivity of liquids, electroplating and electrolysis—appear verbatim in questions and must be used in answers.
✓Most 1-mark questions test identification of good and poor conductors; 2-mark questions demand explanation of LED glowing or electrolysis setup.
✓Three-mark questions frequently ask for electroplating procedure with diagram or applications of chemical effects in daily life.
✓Five-mark questions are case-based, linking electroplating industry or water purification to chemical effects; practice diagram labelling for full credit.
✓Common mistakes include confusing electroplating with electrolysis, writing 'bulb glows' instead of 'LED glows' for weak conductors, and missing safety precautions in answers.
✓CBSETUTOR.ai offers unlimited doubt-solving in Science via photo upload at ₹999/month for any class (6–12); 3-day free trial helps students master diagram-based questions instantly.

Chapter Overview and Marks Weightage in CBSE Exams

Chemical Effects of Electric Current appears in Unit 4 (Electricity and Magnetism) of the CBSE Class 8 Science syllabus. The chapter introduces three core topics: conductivity of liquids, electroplating and electrolysis. In school term exams this chapter typically accounts for 4–6 marks, distributed across one or two MCQs (1 mark each), one short-answer question (2 or 3 marks) and occasionally a case-based or long-answer question (5 marks). The 2024 CBSE sample paper for Class 8 included a 3-mark question on electroplating with diagram and a 1-mark MCQ on identifying good conductors. Diagrams are crucial: expect to label an electrolytic cell, draw the setup for testing conductivity or illustrate the electroplating process. Examiners award 1 mark for a neat, labelled diagram and 2 marks for the explanation. Practice questions from NCERT exercises and exemplar problems ensures coverage of all patterns.

Chapter weight: 4–6 marks in 80-mark term exams
Question types: 1–2 MCQs, 1 short answer (2–3 marks), 1 long/case-based (5 marks)
Diagram compulsory in at least one question (electroplating or conductivity test setup)
NCERT in-text activities (testing tap water, lemon juice, distilled water) often framed as practicals in 2-mark questions

One-Mark Questions: MCQs and Very Short Answers

One-mark questions test recall of definitions, identification of conductors and recognition of chemical effects. CBSE often uses multiple-choice or assertion-reason formats. Students must know that distilled water is a poor conductor while tap water conducts due to dissolved salts, that an LED glows even with weak current (unlike a bulb), and that metals like copper and silver are used in electroplating. Answers should be one-line or single-word where asked. Marks are lost when students write full paragraphs for MCQs or skip units in numerical blanks. Practice at least 10–15 MCQs from NCERT exemplar and previous board papers. Here are five representative questions with answers that match CBSE mark-scheme brevity and precision.

Q1. Which liquid is the best conductor of electricity? (a) Distilled water (b) Tap water (c) Lemon juice (d) Sugar solution. — Answer: (c) Lemon juice (contains citric acid, high ion concentration).
Q2. What is the purpose of using an LED instead of a bulb in a conductivity tester? — Answer: An LED glows even when a weak electric current flows, making it suitable for testing poor conductors.
Q3. Name the process of depositing a layer of any desired metal on another material by means of electricity. — Answer: Electroplating.
Q4. True or False: Pure water (distilled water) is a good conductor of electricity. — Answer: False (distilled water is a poor conductor; tap water conducts due to dissolved salts).
Q5. Which effect of electric current is utilized in electroplating? — Answer: Chemical effect of electric current.

Two-Mark Questions with Model Answers

Two-mark questions demand short explanations, usually in 30–40 words or two distinct points. CBSE Class 8 Science examiners look for use of NCERT terminology, logical sequence and mention of observations where applicable. Questions on why certain liquids conduct electricity, how an LED-based tester works or listing examples of good and poor conductors are common. Each answer should carry two clear ideas: for instance, one sentence stating the property and one giving the reason or example. Avoid writing full essays; stick to bullet points or two concise sentences. Below are four carefully chosen 2-mark questions mirroring actual term-exam patterns, complete with step-by-step marking-scheme aligned answers.

Q6. Explain why tap water conducts electricity but distilled water does not. (2 marks) — Answer: (i) Tap water contains dissolved salts (like sodium chloride) which dissociate into ions; these ions carry electric charge, making tap water a good conductor. (ii) Distilled water has no dissolved salts or minerals, hence no free ions, so it does not conduct electricity.
Q7. What is the role of the liquid in the electroplating process? Give one example. (2 marks) — Answer: (i) The liquid (electrolyte) contains dissolved salt of the metal to be deposited; it allows ions to move between electrodes. (ii) Example: Copper sulphate solution is used to electroplate copper onto an iron spoon.
Q8. List two precautions one must take while testing liquids for electrical conductivity. (2 marks) — Answer: (i) Never use mains supply (220 V); always use a battery of 6–12 V to avoid electric shock. (ii) Clean and dry the electrodes before testing each liquid to prevent contamination and cross-reaction.
Q9. Why does an LED glow even when a weak current flows through it, but a bulb does not? (2 marks) — Answer: (i) An LED is designed to emit light with very small current (in milliamperes), making it sensitive to weak conductors. (ii) A bulb filament requires higher current to heat up and glow; weak current is insufficient to reach the glowing temperature.

Three-Mark Questions with Detailed Answers

Three-mark questions expect a diagram or a three-part explanation. Common topics include describing the electroplating process step-by-step, explaining the conductivity test with a labelled circuit, or listing three applications of chemical effects of electric current. CBSE marking schemes typically allocate 1 mark for the diagram (if asked) and 2 marks for the written points. Students should draw neat, labelled diagrams using a pencil and ruler, marking the battery, electrodes (anode and cathode), electrolyte and direction of current. In the written part, use subheadings or numbers (i), (ii), (iii) for clarity. Below are three representative 3-mark questions with full model answers that score maximum marks under CBSE evaluation guidelines, incorporating NCERT terminology and proper sequencing.

Q10. Describe the process of electroplating a copper vessel with silver. Draw a labelled diagram. (3 marks) — Answer: (Diagram: 1 mark—show battery, silver anode, copper cathode, silver nitrate solution, wires.) (i) The copper vessel is made the cathode (negative terminal) and a pure silver plate is made the anode (positive terminal). (ii) Both are immersed in silver nitrate solution (electrolyte). (iii) When current flows, silver ions from the solution deposit on the copper vessel, forming a uniform silver coating; silver from the anode dissolves to replenish the solution.
Q11. Explain with a diagram how you can test whether a given liquid conducts electricity or not. (3 marks) — Answer: (Diagram: 1 mark—battery, two electrodes (metal rods), LED/bulb, connecting wires, beaker with liquid.) (i) Connect two metal electrodes to the terminals of a battery through an LED or bulb. (ii) Immerse the electrodes in the liquid to be tested, ensuring they do not touch each other. (iii) If the LED glows, the liquid is a conductor; if it does not glow, the liquid is a poor conductor or insulator.
Q12. State three important applications of the chemical effects of electric current in daily life. (3 marks) — Answer: (i) Electroplating: Coating cheaper metals with expensive metals like gold or chromium to prevent corrosion and enhance appearance (e.g. chromium-plated car parts). (ii) Purification of metals: Copper is purified by electrolysis to obtain high-purity copper for electrical wiring. (iii) Electrotyping: Creating metal copies of intricate designs for printing plates and medals by depositing metal on a mould.

Five-Mark Questions and Case-Based Problems

Five-mark questions in CBSE Class 8 Science Chapter 11 are either long answers requiring detailed explanation of a process plus diagram plus applications, or case-based questions that present a real-life scenario followed by sub-questions. A typical long answer might ask students to explain electroplating, draw and label the setup, state two applications and mention one precaution—allocating 1 mark for diagram, 2 for process, 1 for applications and 1 for precaution. Case studies might describe a jewellery shop using electroplating or a water-testing lab, then pose three sub-questions worth 1, 2 and 2 marks. To score full marks, students must read the case carefully, underline keywords, answer in the context given and use NCERT terminology. Here are two complete 5-mark questions with detailed, markscheme-aligned model answers that mirror CBSE board exam standards and recent sample papers.

How CBSE Frames Questions from This Chapter

Understanding the examiner's question-setting pattern helps students anticipate what will be asked and how marks are distributed. CBSE question papers for Class 8 Science Chapter 11 follow predictable templates. MCQs often present four liquids and ask which is the best or poorest conductor; assertion-reason questions pair a statement about electroplating with a reason about ion movement. Two-mark questions probe why a particular liquid conducts or the advantage of using an LED over a bulb. Three-mark questions almost always include a diagram—either the conductivity tester or the electroplating setup—plus an explanation. Five-mark questions are either traditional long answers (process + diagram + applications + precautions) or case studies with real contexts like chrome plating in automobile factories or copper purification in refineries. Examiners award partial marks: for example, in a 3-mark electroplating question, 1 mark goes to the diagram even if the explanation is weak. Keywords matter: writing 'electrolyte' instead of 'solution', 'anode' and 'cathode' instead of 'positive and negative electrode', and 'deposition of ions' instead of 'metal sticks' earns you full credit. Recent CBSE sample papers (2023, 2024) show increased use of practical-based questions—describing NCERT activities, suggesting modifications or predicting outcomes when one component is changed.

MCQs test recognition of good/poor conductors and definitions (electroplating, electrolysis, LED advantage)
Two-mark questions demand explanation in two points: property + reason or example
Three-mark questions require diagram (1 mark) + explanation (2 marks); neatness and labelling critical
Five-mark questions split into process (2 marks), diagram (1 mark), applications (1 mark), precaution (1 mark) or case study with 3 sub-questions
Partial marking: even if explanation is incomplete, a correct labelled diagram fetches 1 mark
Use NCERT terms: 'electrolyte', 'anode', 'cathode', 'deposition', 'dissociation of salts'—generic words reduce marks

Common Mistakes Students Make and How to Avoid Them

Every year, CBSE Class 8 Science answer scripts lose easy marks on Chapter 11 due to recurring errors. Many students write 'the bulb glows' instead of 'the LED glows', forgetting that the NCERT activity uses an LED because weak conductors do not provide enough current for a bulb filament. Another frequent mistake is confusing electroplating with electrolysis: electroplating deposits one metal onto another object, while electrolysis is the broader chemical decomposition by electric current (for example, splitting water into hydrogen and oxygen). Diagrams suffer when students forget to label the anode and cathode or draw wires that do not connect to battery terminals; examiners deduct 0.5 marks for each missing or incorrect label. In explanations, vague phrases like 'metal gets deposited' score less than precise statements such as 'positive metal ions from the electrolyte gain electrons at the cathode and deposit as neutral metal atoms'. Students also omit units (writing 6 V as just 6) or safety points (never mentioning low voltage or dry hands). Finally, many skip reading the question carefully: a question asking for 'two applications of electroplating' should list specific examples (chromium plating on taps, gold plating on jewellery), not generic 'it is used in industries'. Practising with the NCERT exemplar and reviewing marking schemes before exams eliminates most of these pitfalls.

Mistake 1: Writing 'bulb' instead of 'LED'—NCERT uses LED in conductivity tester; always write LED in answers.
Mistake 2: Confusing electroplating (coating an object) with electrolysis (chemical decomposition); state the purpose clearly.
Mistake 3: Unlabelled or incomplete diagrams—mark anode (+), cathode (−), electrolyte, battery terminals; use ruler and pencil.
Mistake 4: Vague language—'metal sticks to spoon' loses marks; write 'metal ions deposit on the cathode surface'.
Mistake 5: Forgetting units and precautions—always mention 6 V battery, dry hands, clean electrodes in process answers.
Mistake 6: Not reading the question—if asked for two applications, give exactly two with examples; extra points do not earn bonus marks.

Quick Revision Tips and Exam Strategy

With only 4–6 marks at stake, smart students focus revision on high-yield areas: memorise the NCERT list of good conductors (tap water, lemon juice, salt solution) and poor conductors (distilled water, sugar solution), practice drawing the electroplating diagram until labelling becomes automatic, and learn three clear applications of electroplating by heart. Allocate 10 minutes in your exam to the Chapter 11 question: spend 2 minutes reading and planning, 5 minutes writing and 3 minutes drawing and labelling the diagram. Use bullet points or numbering (i), (ii), (iii) to organise answers, as examiners can quickly locate mark-worthy points. For case-based questions, underline keywords in the passage—'LED glows', 'sugar solution', 'cathode'—and refer to them in your sub-answers. Revise one day before the exam by solving the NCERT exercise, the exemplar MCQs and at least two previous-year questions. Make a one-page formula sheet listing process steps for electroplating, the conductivity test procedure and standard precautions; read it 30 minutes before entering the exam hall. During the exam, if a 5-mark question offers choice between a long answer and a case study, pick the format you have practised more. Finally, always attempt the diagram question: even if your explanation is weak, a well-labelled diagram fetches you 1 sure mark.

Memorise NCERT lists: good conductors (tap water, lemon juice, salt solution) vs poor conductors (distilled water, sugar solution, alcohol)
Practice diagrams daily: electroplating setup and conductivity tester; aim for neat, labelled drawings in under 3 minutes
Learn 3 applications of electroplating word-for-word: chromium plating on taps, gold plating on jewellery, tin coating on iron cans
Time management: 2 min reading + 5 min writing + 3 min diagram for a 5-mark question
One-page revision sheet: process steps, key terms (electrolyte, anode, cathode, deposition), safety precautions
Attempt diagram questions first: guaranteed 1 mark even if explanation is incomplete; builds confidence

How CBSETUTOR.ai Helps Master This Chapter

Parents in cities like Delhi, Mumbai and Bengaluru often find that Class 8 students struggle with diagram-based Science questions and need instant doubt-clearing, especially before term exams. CBSETUTOR.ai offers an AI tutor available 24×7 that accepts photo uploads of questions—students snap a picture of the electroplating diagram or a tricky MCQ from their worksheet and receive step-by-step solutions within seconds. Unlike expensive coaching centres charging ₹5,000–₹10,000 per subject, CBSETUTOR.ai costs a flat ₹999/month for any class from 6 to 12, covering all subjects including Science. The platform aligns answers with CBSE marking schemes, uses NCERT terminology and even suggests how to draw and label diagrams for maximum marks. During the 3-day free trial, students can upload unlimited questions from Chapter 11—conductivity tests, electroplating processes, case studies—and see exactly how examiners expect answers to be structured. For a working parent who cannot sit through every doubt session after office hours, CBSETUTOR.ai ensures the child never gets stuck on a question, builds confidence through instant feedback and revises efficiently without dependence on weekend tuition classes.

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Frequently asked questions

How many marks does Chapter 11 Chemical Effects of Electric Current carry in CBSE Class 8 Science exams?+

This chapter typically carries 4–6 marks in an 80-mark term exam, split into 1–2 MCQs (1 mark each), one short answer (2–3 marks) and sometimes one long or case-based question (5 marks). The 2024 CBSE sample paper included a 3-mark electroplating question and a 1-mark MCQ on conductors.

What are the three main topics in NCERT Class 8 Science Chapter 11?+

The three core topics are conductivity of liquids (testing which liquids conduct electricity), electroplating (depositing a metal layer on another material using electric current) and electrolysis (chemical decomposition by electricity). All three appear in exam questions and in-text NCERT activities.

Why do we use an LED instead of a bulb in a conductivity tester?+

An LED glows even when a very weak electric current flows through it, making it sensitive enough to detect poor conductors like tap water. A bulb requires much higher current to heat the filament and glow, so it will not light up with weak conductors. CBSE awards 1 mark for this explanation in 1-mark questions.

What is the difference between electroplating and electrolysis?+

Electroplating is the process of coating one metal onto another object for protection or appearance, using electric current and an electrolyte solution. Electrolysis is the broader chemical process where electric current decomposes a compound into elements, such as splitting water into hydrogen and oxygen. Confusing the two costs marks in exams.

Which liquids are good conductors and which are poor conductors of electricity?+

Good conductors include tap water, lemon juice, salt solution and dilute acids because they contain dissolved salts that dissociate into ions. Poor conductors include distilled water, sugar solution and alcohol, as they have no or very few free ions. NCERT lists these explicitly; memorise both groups for MCQs.

How should I draw the electroplating diagram to get full marks?+

Use a pencil and ruler. Label the battery with + and − terminals, mark the object to be plated as cathode (−), the pure metal plate as anode (+), show both immersed in electrolyte solution and draw connecting wires clearly. A neat, fully labelled diagram earns 1 mark even if the written explanation is weak.

What are two common applications of electroplating asked in exams?+

Chromium plating on car parts and bathroom taps (prevents rusting, gives shiny finish) and gold plating on cheaper metal jewellery (reduces cost, retains appearance) are the two most frequently asked examples. Tin coating on iron cans to prevent corrosion is another valid answer. State specific examples, not generic 'used in industries'.

What safety precautions should I mention in electroplating or conductivity test answers?+

Always write: use a low-voltage battery (6 V or 9 V), never connect to mains supply (220 V); do not touch electrodes or wires with wet hands; clean and dry electrodes before each test; ensure electrodes do not touch each other in the liquid. Mentioning even one precaution can fetch 1 mark in a 5-mark answer.

How can I score full marks in a 5-mark case-based question on this chapter?+

Read the case passage carefully and underline keywords (LED, tap water, anode, cathode). Answer each sub-question separately, using the context given in the passage. Use NCERT terminology (electrolyte, deposition, dissociation). Allocate marks mentally—1-mark sub-questions need one clear point, 2-mark need two points—and write accordingly. Practice previous case studies to build speed.

Why does distilled water not conduct electricity but tap water does?+

Distilled water is pure H₂O with no dissolved salts, so it has no free ions to carry electric charge; hence it is a poor conductor. Tap water contains dissolved minerals like sodium chloride, calcium and magnesium salts that dissociate into ions, enabling it to conduct electricity. This 2-mark explanation appears frequently in CBSE exams.

What is the role of the electrolyte solution in electroplating?+

The electrolyte contains dissolved salt of the metal to be deposited (e.g. copper sulphate for copper plating). It provides metal ions that move towards the cathode (object to be plated) and deposit there. It also allows electric current to flow between anode and cathode. Always name a specific electrolyte example for full marks.

How does CBSETUTOR.ai help with Chapter 11 questions and diagrams?+

CBSETUTOR.ai lets students upload a photo of any question—MCQ, diagram-based or case study—and receive an instant, step-by-step solution aligned with CBSE marking schemes. The AI tutor shows how to label diagrams correctly, uses NCERT terminology and costs only ₹999/month for all subjects and classes 6–12. A 3-day free trial allows unlimited practice on electroplating and conductivity questions before exams.

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