Class 8 Science (CTET Paper 2)Critical (2–3 MCQs guaranteed)9 min read
Chapter 4: Materials: Metals and Non-Metals
पदार्थ: धातु और अधातु (भौतिक व रासायनिक गुण, विस्थापन अभिक्रियाएँ)
CTET Theme: Materials & Chemical Reactions
CTET Medium / परीक्षा माध्यम:Toggle authentic CBSE terminology
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OVERVIEW1 of 11
Introduction: Materials: Metals and Non-Metals
Welcome to Mentora CTET Audio Masterclass for Class 8 Science (CTET Paper 2), Chapter 4: Materials: Metals and Non-Metals. Here are the high-yield facts tested in CBSE examinations.
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High-Weightage NCERT Facts & Key Terms (द्विभाषी)
7 Core Points- Physical properties of metals: Malleability (beaten into thin sheets, e.g. gold, silver, aluminum foil), Ductility (drawn into thin wires, e.g. copper, gold), Sonorous (produces ringing sound), Lustrous, Good conductors of heat and electricity.
- Exceptions to physical properties: Mercury is the only liquid metal at room temperature; Sodium and Potassium are soft metals easily sliced with a butter knife; Graphite (carbon non-metal) is an excellent conductor of electricity; Diamond (carbon non-metal) is the hardest known natural substance; Iodine is a non-metal with bright metallic lustre.
- Reaction of metals with oxygen: Forms basic metal oxides that turn moist red litmus paper BLUE (e.g., 2Mg + O2 -> 2MgO; MgO + H2O -> Mg(OH)2).
- Reaction of non-metals with oxygen: Forms acidic non-metal oxides that turn moist blue litmus paper RED (e.g., S + O2 -> SO2; SO2 + H2O -> H2SO3 sulphurous acid).
- Reaction with acids: Metals react with dilute hydrochloric or sulphuric acid releasing Hydrogen gas (H2), which burns with a characteristic 'POP' sound when tested with a burning matchstick. Non-metals generally do not react with dilute acids.
- Reactivity Series & Displacement Reactions: A more reactive metal displaces a less reactive metal from its aqueous salt solution (e.g. Fe + CuSO4 -> FeSO4 + Cu; blue copper sulphate turns light green with reddish copper deposit). A less reactive metal cannot displace a more reactive metal (Cu cannot displace Fe from FeSO4).
- Storage hazards: Sodium and Potassium stored submerged in kerosene because they react violently with atmospheric moisture and oxygen; Non-metal Phosphorus stored submerged in water because it spontaneously ignites in air.
CBSE Distractor Traps (Avoid Negative Marking)
- Trap: CBSE asks what gas produces a 'POP' sound with a burning splinter. Correct: HYDROGEN gas (not oxygen, not CO2).
- Trap: CBSE asks which metal is stored in kerosene. Correct: SODIUM and POTASSIUM. Which non-metal is stored in water? PHOSPHORUS.
- Trap: Nature of metal vs non-metal oxides. Correct: Metal oxides are BASIC (turn red litmus blue); non-metal oxides are ACIDIC (turn blue litmus red).
NCERT Core Facts: Metals, Non-Metals & Reaction Chemistry
CTET Paper 2 Science tests physical exceptions, litmus color changes for oxides, hydrogen gas pop tests, and displacement series.
1. Physical Properties & Key Exceptions
| Property | Standard Observation | Critical Scientific Exceptions (CTET Traps) |
|---|---|---|
| Physical State | Metals are solid at room temperature | Mercury ($Hg$) is liquid at room temperature. |
| Hardness | Metals are hard and rigid | Sodium ($Na$) and Potassium ($K$) are so soft they can be sliced with a knife. |
| Malleability | Metals can be hammered into thin sheets (Gold, Silver, Aluminium) | Non-metals are brittle and shatter into powder when hammered. |
| Ductility | Metals can be drawn into thin wires (Copper, Gold) | Non-metals are completely non-ductile. |
| Electrical Conductivity | Metals conduct electricity | Graphite (a non-metal allotrope of carbon) is an excellent electrical conductor. |
| Lustre | Metals have a shiny surface | Iodine is a non-metal that possesses bright metallic lustre. |
| Hardness | Non-metals are generally soft or gaseous | Diamond (allotrope of carbon) is the hardest known natural substance. |
2. Chemical Properties & Diagnostic Tests
A. Reaction with Oxygen (Oxide Acidity/Basicity)
- Metals: Produce basic oxides.
2\text{Mg} + \text{O}_2 → 2\text{MgO} \quad ; \quad \text{MgO} + \text{H}_2\text{O} → \text{Mg(OH)}_2
- Diagnostic Litmus Test: Magnesium hydroxide turns moist Red Litmus $\rightarrow$ Blue.
- Non-Metals: Produce acidic oxides.
\text{S} + \text{O}_2 → \text{SO}_2 \quad ; \quad \text{SO}_2 + \text{H}_2\text{O} → \text{H}_2\text{SO}_3 \text{ (Sulphurous acid)}
- Diagnostic Litmus Test: Sulphurous acid turns moist Blue Litmus $\rightarrow$ Red.
B. Reaction with Acids (The Hydrogen 'POP' Test)
- Metal + Dilute Acid $\rightarrow$ Salt + Hydrogen Gas ($H_2$)
- When a burning splinter or matchstick is brought near the mouth of the test tube, the escaping gas burns with a distinctive 'POP' sound.
- Non-metals generally do not react with dilute acids.
C. Displacement Reactions (Reactivity Hierarchy)
- Rule: A more reactive metal displaces a less reactive metal from its salt solution.
\text{Fe} + \text{CuSO}_4 \text{ (Blue)} → \text{FeSO}_4 \text{ (Light Green)} + \text{Cu} \text{ (Reddish brown)}
\text{Zn} + \text{CuSO}_4 → \text{ZnSO}_4 \text{ (Colourless)} + \text{Cu}
- A less reactive metal cannot reverse the displacement:
\text{Cu} + \text{FeSO}_4 → \text{No Reaction}
\text{Cu} + \text{ZnSO}_4 → \text{No Reaction}
3. Storage Safety Benchmarks
- Sodium and Potassium: Highly reactive metals; catch fire in air and react explosively with water → Stored submerged under kerosene.
- Phosphorus: Highly reactive non-metal; spontaneously catches fire on contact with atmospheric oxygen → Stored submerged under water.
Official CTET Benchmark Test
Test Your Mastery: Materials: Metals and Non-Metals
Authentic CBSE exam questions tested directly from this NCERT chapter.
Question 1 of 3(CTET July 2019 / Dec 2021)
Which of the following non-metals is stored in water to prevent it from catching fire on contact with air?
निम्नलिखित में से किस अधातु को वायु के संपर्क में आने से आग पकड़ने से रोकने के लिए जल में रखा जाता है?
Question 2 of 3(CTET Dec 2019 / Jan 2022)
A metal 'X' is soft, can be cut with a knife, and reacts vigorously with water. Metal 'X' is:
एक धातु 'X' इतनी मुलायम है कि उसे चाकू से काटा जा सकता है और वह जल के साथ तीव्र अभिक्रिया करती है। वह धातु 'X' है:
Question 3 of 3(CTET Dec 2021 / Aug 2023)
When dilute hydrochloric acid is added to zinc granules in a test tube, a gas is evolved that burns with a 'pop' sound. This gas is:
जब एक परखनली में जिंक के दानों में तनु हाइड्रोक्लोरिक अम्ल मिलाया जाता है, तो एक गैस निकलती है जो 'पॉप' ध्वनि के साथ जलती है। यह गैस है:
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Which metal is stored in kerosene and why?
Sodium and potassium, because they react vigorously with air and moisture, producing explosive heat.
Which gas burns with a pop sound when metals react with acid?
Hydrogen gas (H2) produces a characteristic pop sound when ignited.
Why is phosphorus stored in water?
Phosphorus is a highly reactive non-metal that catches fire when exposed to air, but does not react with water.