This MCQ module is based on: Uses of Metals, Rusting and Its Prevention
TOPIC 13 OF 46
Uses of Metals, Rusting and Its Prevention
🎓 Class 7
Science
CBSE
Theory
Ch 4 — The World of Metals and Non-metals
⏱ ~14 min
🌐 Language: [gtranslate]
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4.3 Effect of Air and Water on Metals — Rusting
After the first monsoon shower, Anandi notices a strange reddish-brown coating on the new iron gate and on her father's bicycle chain. Her grandmother sighs — "This is zang (rust). It eats away our iron tools over time." This reddish-brown coating is called rust.
4 Fe + 3 O2 + n H2O → 2 Fe2O3·n H2O (reddish-brown rust)
Conditions Needed for Rusting
Does iron rust in just any condition? Let us find out.
Activity 4.8 — The Three Test Tubes L3 Apply
Take three clean test tubes A, B, C and place one fresh iron nail in each.
- Tube A: Half fill with boiled water (boiling removes dissolved air). Add a layer of oil on top to stop air entering. Water only.
- Tube B: Put anhydrous calcium chloride (CaCl2) at the bottom to absorb moisture. Seal with a cork. Dry air only.
- Tube C: Half fill with ordinary tap water and leave open. Water + air.
Observe all three tubes after a few days.
Predict: In which tube will the nail rust the most?
Only the nail in Tube C rusts — there, iron had access to both air (oxygen) and water (moisture). Tubes A and B each lack one of these, so no rust forms. Conclusion: Rusting needs both oxygen and moisture.
Why does rust matter? Rust makes iron flaky and weak. Bridges, railway tracks, car bodies, farm tools and even water pipes can fail if they rust badly — costing lives and money.
4.3.1 Prevention of Rusting
The trick is simple: keep iron away from either air or water. Here are the common methods.
| Method | How it works | Where it is used |
|---|---|---|
| Painting / Oiling / Greasing | Adds a thin barrier that blocks air and moisture | Gates, windows, cycle chains, machinery |
| Galvanisation | A layer of zinc is coated on iron. Zinc is more reactive, so it reacts first and protects the iron underneath. | Roofing sheets, buckets, electric poles |
| Chromium plating | A shiny chromium coating resists rust and looks attractive | Car bumpers, taps, surgical tools |
| Alloying | Iron is mixed with chromium & nickel to form stainless steel, which does not rust | Kitchen utensils, cutlery, surgical tools |
| Proper storage | Keep iron tools dry and oiled in a well-ventilated place | Homes, workshops, warehouses |
Interactive: Protect the Iron Nail
Choose a prevention method and see what happens to the nail after one monsoon season!
Pick a method above to see the outcome.
4.4 Uses of Metals
Metals are everywhere — in the building we live in, the vehicle we travel in, the spoon we eat with, the bell we ring at the temple, and the phone we hold. Here are eight major uses.
Construction
Iron rods, steel girders for buildings, bridges and flyovers
Transport
Cars, trains and aeroplanes use steel, iron and aluminium
Cooking
Utensils of steel, copper, aluminium and iron
Electrical
Copper and aluminium wires; gold for tiny contacts in phones
Jewellery
Gold, silver and platinum — bright, lustrous, non-tarnishing
Coins
Copper, nickel and aluminium are hard-wearing and cheap
Machinery
Engines, gears, pumps — all rely on strong metal parts
Agriculture
Iron-based spades, sickles, ploughs and rakes
4.5 Uses of Non-metals
Though fewer in number, non-metals are just as vital. We breathe oxygen, eat food grown with nitrogen fertilisers, and write with graphite pencils every day!
Oxygen (O₂)
Breathing; supports burning of fuels; medical use in hospitals
Nitrogen (N₂)
78% of air; used in urea fertilisers and food packets
Hydrogen (H₂)
Rocket fuel; weather balloons; raw material for ammonia
Carbon (C)
Coal as fuel; graphite in pencils; diamonds in cutting & jewellery
Sulphur (S)
Sulphur ointments; sulphuric acid; gunpowder
Phosphorus (P)
Match-stick heads; fertilisers; detergents
Chlorine (Cl₂)
Water purification; bleaching; disinfectants
Iodine (I)
Antiseptic (tincture of iodine); iodised salt for thyroid health
Link with Ch 3: The copper wires inside electric cables, the graphite rod inside a dry cell and the zinc outer case are all examples of this chapter's metals and non-metals at work!
Competency-Based Questions L4 Analyse
Sameera buys a new iron gate for her house. The shopkeeper offers three options: (i) a painted black gate, (ii) a galvanised gate, (iii) a stainless steel gate. She lives in Mumbai, which faces heavy rain for 4 months a year. Her budget allows all three.
1. Which of these needs re-painting every 2–3 years?
Option (i) — painted gate. The paint layer eventually chips, exposing bare iron which then rusts.
2. Why will the galvanised gate last longer than the painted one?
Zinc is more reactive than iron; it reacts with air and moisture first, sacrificing itself to protect the iron. The protection continues even if the zinc coat is slightly scratched.
3. Stainless steel does not rust. Give two metals it contains apart from iron.
Chromium and nickel.
4. Why do we use copper for wires but not iron wires for home wiring?
Copper is a far better conductor of electricity than iron and does not rust easily, so electrical losses and maintenance are low.
5. True/False: Iron rusts even in completely dry air.
False. Rusting requires both oxygen and moisture. Dry air alone does not cause rust.
Assertion–Reason Questions
(A) Both true, R explains A • (B) Both true, R does not explain A • (C) A true, R false • (D) A false, R true.
A: Kitchen utensils are often made of stainless steel.
R: Stainless steel is an alloy of iron, chromium and nickel that does not rust.
(A) — The rust-free nature of stainless steel is exactly why it is used in utensils.
A: Oxygen is used in hospitals for patients with breathing difficulty.
R: Oxygen is a metal essential for respiration.
(C) — Assertion is true, but oxygen is a non-metal, so R is false.
A: Graphite is used to make the 'lead' of pencils.
R: Graphite is a soft, black form of carbon that leaves a mark on paper and also conducts electricity.
(A) — Graphite's softness and marking ability (its physical properties) make it perfect for pencils.
Frequently Asked Questions — Uses of Metals, Rusting and Its Prevention
What does the topic 'Uses of Metals, Rusting and Its Prevention' cover in Class 7 Science?
The topic 'Uses of Metals, Rusting and Its Prevention' is part of NCERT Class 7 Science Chapter 4 — The World of Metals and Non-metals. It covers the key ideas of uses of metals, rusting, prevention, galvanisation, painting, oiling, alloys, explained through everyday examples, labelled diagrams and hands-on activities drawn from the NCERT Curiosity textbook. Students learn not just definitions but also the reasoning behind each concept so they can answer competency-based questions and assertion–reason items. The lesson helps Class 7 students build a strong base for higher classes by linking each idea to real observations at home, school and in nature, and by preparing them for CBSE school assessments and Olympiads.
Why is 'Uses of Metals, Rusting and Its Prevention' important for Class 7 NCERT Science?
'Uses of Metals, Rusting and Its Prevention' is important because it builds core scientific thinking that Class 7 students will use throughout middle and secondary school. NCERT Chapter 4 — The World of Metals and Non-metals — introduces uses of metals and related ideas that appear again in Class 8, 9 and 10 Science. Mastering this subtopic helps students read labels and safety signs, understand news about science and technology, and perform better in CBSE school exams. The chapter also encourages curiosity and evidence-based thinking — skills that support the National Education Policy (NEP) 2020 focus on conceptual understanding and competency-based learning.
What are the key concepts students should remember from Uses of Metals, Rusting and Its Prevention?
The key concepts in 'Uses of Metals, Rusting and Its Prevention' for Class 7 Science are: uses of metals, rusting, prevention, galvanisation, painting, oiling, alloys. Students should be able to define each term in their own words, give at least one everyday example, and explain how the concept connects to other chapters in NCERT Class 7 Science. For example, linking the idea to daily life — in the kitchen, classroom or outdoors — makes revision easier. Writing short notes, drawing labelled diagrams and solving the NCERT in-text and exercise questions for Chapter 4 will help students retain these concepts for unit tests and the annual CBSE examination.
How is Uses of Metals, Rusting and Its Prevention taught using activities in NCERT Curiosity Class 7?
NCERT Curiosity Class 7 Science teaches 'Uses of Metals, Rusting and Its Prevention' using an inquiry-based approach with Predict–Observe–Explain activities. Students are asked to make a guess first, then perform a simple experiment with safe, easily available materials, and finally explain what they observed. This matches the NEP 2020 focus on learning by doing. For Chapter 4 — The World of Metals and Non-metals — the textbook includes hands-on tasks, labelled diagrams and questions that build Bloom's Taxonomy skills from Remember (L1) to Create (L6). Teachers use these activities, along with competency-based questions (CBQs) and assertion–reason items, to check real understanding rather than rote memorisation.
What real-life examples of uses of metals can Class 7 students observe at home?
Class 7 students can observe uses of metals at home in many simple ways linked to 'Uses of Metals, Rusting and Its Prevention'. Kitchens, school bags, playgrounds and the night sky are full of examples that connect to NCERT Chapter 4 — The World of Metals and Non-metals. For instance, students can check labels on food and cleaning products, watch changes while cooking, or observe the Sun and Moon across a week. Keeping a small science diary — noting the date, what was observed and a quick sketch — turns everyday life into a science lab. These real-life connections make concepts stick and prepare students well for competency-based questions in CBSE Class 7 Science.
How does 'Uses of Metals, Rusting and Its Prevention' connect to other chapters of Class 7 Science?
'Uses of Metals, Rusting and Its Prevention' connects to many other chapters in NCERT Class 7 Science Curiosity. The ideas of uses of metals appear again when students study related topics like heat, light, changes, life processes and Earth-Sun-Moon. For example, understanding this subtopic helps in building mental models for later chapters and for Class 8, 9 and 10 Science. Teachers often use cross-chapter questions in CBSE examinations to test whether students can apply what they learned in Chapter 4 — The World of Metals and Non-metals — to new situations. This integrated approach matches the NEP 2020 and NCF 2023 focus on holistic, competency-based learning.
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