📘 Metals and Non-metals — Answers
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✅ Q1.
Which pairs will give displacement reactions?
Displacement happens when a more reactive metal displaces a less reactive one from its compound.
• (a) NaCl & Cu → ❌ (Cu is less reactive than Na)
• (b) MgCl₂ & Al → ❌ (Al is less reactive than Mg)
• (c) FeSO₄ & Ag → ❌ (Ag is less reactive than Fe)
• (d) AgNO₃ & Cu → ✅ (Cu displaces Ag)
🎯 Answer: (d) AgNO₃ solution and copper metal
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✅ Q2.
Preventing rust on an iron frying pan:
• (a) grease → ✅
• (b) paint → ✅
• (c) zinc coating → ✅
🎯 Answer: (d) All of the above
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✅ Q3.
An element forms a high-melting, water-soluble oxide → likely a metal →
🎯 Answer: (a) Calcium
(Ca + O₂ → CaO, which is soluble & high melting)
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✅ Q4.
Food cans are coated with tin (Sn) & not zinc (Zn) because:
• Zinc is more reactive → can react with food.
🎯 Answer: (c) zinc is more reactive than tin
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✅ Q5.
(a) Distinguishing metals & non-metals:
• Use hammer → metals are malleable; non-metals break.
• Make circuit with battery, bulb, wires → metals conduct & light bulb; non-metals don’t.
(b) Usefulness:
• Simple & effective but only works for solid samples & does not work if surface is oxidised or coated.
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✅ Q6.
Amphoteric oxides:
🎯 Oxides that react with both acids & bases to form salt & water.
Examples:
• Aluminium oxide (Al₂O₃)
• Zinc oxide (ZnO)
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✅ Q7.
Metals that displace H₂ from dilute acids:
✅ Zinc, Magnesium
Metals that do not:
❌ Copper, Silver
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✅ Q8.
Electrolytic refining of metal M:
• Anode → impure metal M
• Cathode → pure metal M
• Electrolyte → solution of salt of metal M
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✅ Q9.
Sulphur is heated → forms sulphur dioxide gas.
(a) Action of gas:
• On dry litmus → no change
• On moist litmus → turns blue litmus red (acidic gas)
(b) Reaction:
S + O₂ → SO₂
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✅ Q10.
Two ways to prevent rusting of iron:
• Applying oil/grease/paint
• Coating with zinc (galvanisation)
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✅ Q11.
Oxides formed when non-metals combine with oxygen:
🎯 Acidic or neutral oxides.
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✅ Q12.
Reasons:
(a) Platinum, gold & silver → used in jewellery because they are shiny, malleable & do not corrode.
(b) Na, K, Li → stored under oil because they react vigorously with air & water.
(c) Aluminium → forms a protective oxide layer, so despite being reactive, it resists corrosion.
(d) Carbonate & sulphide ores → converted to oxides because oxides are easier to reduce to metal.
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✅ Q13.
Why lemon/tamarind cleans copper?
🎯 Copper reacts with oxygen & CO₂ to form greenish copper carbonate layer (tarnish). Acids in lemon/tamarind dissolve this layer.
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✅ Q14.
Difference between metals & non-metals (chemical properties):
Property Metals Non-metals
Oxides Basic or amphoteric Acidic or neutral
Reaction with acids Produces H₂ No reaction
Reaction with oxygen Forms basic oxides Forms acidic oxides
Reaction with water Some react Usually no reaction
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✅ Q15.
Detective story:
🎯 The man used aqua regia (HCl + HNO₃).
It dissolves gold by forming soluble chloroauric acid → ornaments shine but lose gold.
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✅ Q16.
Why copper for hot water tanks & not steel?
🎯 Copper does not corrode easily in water & conducts heat well, whereas steel (iron alloy) rusts in moist conditions.
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