Metals and Non-metals

Correct Option: (d) AgNO₃ solution and copper metal

Explanation:
Displacement reactions occur when a more reactive metal displaces a less reactive metal from its compound.

• (a) NaCl + Cu: No reaction (Cu less reactive than Na)
• (b) MgCl₂ + Al: No reaction (Al less reactive than Mg)
• (c) FeSO₄ + Ag: No reaction (Ag less reactive than Fe)
• (d) AgNO₃ + Cu: Cu is more reactive than Ag, so displacement occurs:
2AgNO₃(aq) + Cu(s) → Cu(NO₃)₂(aq) + 2Ag(s)

Correct Option: (d) All of the above

Explanation:
All methods create a protective barrier between iron and moisture/oxygen:

• Grease/Oiling: Forms waterproof coating
• Painting: Creates physical barrier
• Galvanizing (Zn coating): Zinc sacrifices itself (acts as anode) even if coating is broken
Note: For cooking utensils, galvanizing is most durable, while grease/paint may wear off with heat and cleaning.

Correct Option: (a) calcium

Explanation:
• Calcium reacts with oxygen: 2Ca + O₂ → 2CaO
• Calcium oxide (CaO) has a high melting point (2572°C).
• CaO reacts with water: CaO + H₂O → Ca(OH)₂
• Calcium hydroxide is soluble in water (forms limewater).

Others: Carbon gives CO/CO₂ (gases), silicon gives SiO₂ (insoluble), iron gives Fe₂O₃/Fe₃O₄ (insoluble in water).

Correct Option: (c) zinc is more reactive than tin

Explanation:
• Zinc is more reactive than tin (see reactivity series).
• More reactive metals can react with acidic food components.
• Tin is less reactive and forms a stable, non-toxic layer.
• Zinc coating might impart taste and could be toxic if it reacts with food acids.
• Note: For water pipes and structural steel, zinc (galvanizing) is preferred as it provides sacrificial protection.

(a) Procedure:
1. Malleability test: Hit samples with hammer. Metals flatten (malleable), non-metals shatter (brittle).
2. Electrical conductivity: Make circuit with battery, bulb, wires. Place sample between wires. Metals conduct (bulb glows), non-metals don't (except graphite).

(b) Usefulness assessment:
• Malleability test: Good but some metals (Na, K too soft), some non-metals (diamond hard).
• Electrical test: Very reliable for distinguishing (except graphite exception).
• Combined tests give accurate identification.

Amphoteric oxides are metal oxides that react with both acids and bases to form salt and water.

Examples:
1. Aluminium oxide (Al₂O₃):
With acid: Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O
With base: Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O

2. Zinc oxide (ZnO):
With acid: ZnO + 2HCl → ZnCl₂ + H₂O
With base: ZnO + 2NaOH → Na₂ZnO₂ + H₂O

Other examples: Lead oxide (PbO), tin oxide (SnO).

Metals that displace H₂ from dilute acids:
• Zinc (Zn): Zn + 2HCl → ZnCl₂ + H₂
• Magnesium (Mg): Mg + H₂SO₄ → MgSO₄ + H₂
• Also: Iron, aluminium, sodium, potassium (all metals above H in reactivity series)

Metals that do NOT displace H₂ from dilute acids:
• Copper (Cu): Below H in reactivity series
• Silver (Ag): Below H in reactivity series
• Also: Gold, platinum, mercury

Rule: Only metals above hydrogen in reactivity series can displace it from acids.

Electrolytic Refining Setup:

• Anode: Impure metal M
• Cathode: Thin strip of pure metal M
• Electrolyte: Salt solution of metal M (e.g., CuSO₄ for copper refining)

Process (example: Copper):
1. At anode: Cu → Cu²⁺ + 2e⁻ (impure copper dissolves)
2. At cathode: Cu²⁺ + 2e⁻ → Cu (pure copper deposits)
3. Impurities: Less reactive settle as anode mud (Au, Ag, Pt); more reactive go into solution.

Reaction: Sulphur burns in air to form sulphur dioxide.
S(s) + O₂(g) → SO₂(g)

(a) Action of SO₂ gas:
• (i) Dry litmus paper: No change (SO₂ needs water to form acid)
• (ii) Moist litmus paper: Turns red (SO₂ dissolves in water to form sulphurous acid)
SO₂(g) + H₂O(l) → H₂SO₃(aq)

Key point: Non-metal oxides are acidic in nature.

Methods to prevent rusting:

1. Barrier Protection:
• Painting, oiling, greasing, plastic coating
• Creates physical barrier between iron and moisture/oxygen

2. Sacrificial Protection:
• Galvanizing (coating with zinc)
• Zinc is more reactive than iron, so it corrodes first
• Even if coating breaks, zinc protects iron

Other methods: Alloying (stainless steel), chrome plating, anodizing, cathodic protection.

Non-metals form acidic or neutral oxides when combined with oxygen.

Acidic Oxides (Majority):
• Sulphur dioxide: SO₂ (forms H₂SO₃ with water)
• Carbon dioxide: CO₂ (forms H₂CO₃ with water)
• Phosphorus pentoxide: P₄O₁₀ (forms H₃PO₄ with water)
• Nitrogen dioxide: NO₂ (forms HNO₃ with water)

Neutral Oxides (Few):
• Carbon monoxide: CO
• Nitrous oxide: N₂O
• Water: H₂O

Note: Non-metals do not form basic oxides.

(a) Platinum, gold, silver are least reactive (noble metals), don't tarnish/corrode easily, malleable/ductile for shaping, and have lustrous appearance.

(b) Sodium, potassium, lithium are highly reactive with air/moisture. They react violently with oxygen (catch fire) and water. Oil prevents contact with air/moisture.

(c) Aluminium forms a protective oxide layer (Al₂O₃) that prevents further reaction. This makes it corrosion-resistant despite high reactivity. Also lightweight, good conductor of heat.

(d) Oxides are easier to reduce to metals compared to sulphides/carbonates. Carbon (coke) can reduce metal oxides but not directly sulphides/carbonates. Conversion steps:
• Sulphides → Oxides (Roasting): 2ZnS + 3O₂ → 2ZnO + 2SO₂
• Carbonates → Oxides (Calcination): ZnCO₃ → ZnO + CO₂

• Copper vessels tarnish due to formation of basic copper carbonate (CuCO₃·Cu(OH)₂) – green layer.
• Lemon/tamarind juice contains citric acid/tartaric acid (weak organic acids).
• Acid reacts with basic copper carbonate:
CuCO₃·Cu(OH)₂ + 4H⁺ (from acid) → 2Cu²⁺ + CO₂ + 3H₂O
• This dissolves the tarnish layer, revealing shiny copper underneath.
• Similar principle: Vinegar (acetic acid) also works.

Property	Metals	Non-metals
Reaction with oxygen	Form basic oxides 4Na + O₂ → 2Na₂O	Form acidic/neutral oxides C + O₂ → CO₂
Reaction with water	React to form metal hydroxide + H₂ (Na, K violently; Fe with steam)	Generally no reaction
Reaction with acids	Displace H₂ (metals above H in series)	No reaction (no H₂ displacement)
Reaction with bases	Some amphoteric metals react (Al, Zn)	Some react (e.g., Si, P)
Displacement reactions	More reactive displaces less reactive	More reactive displaces less reactive
Ion formation	Lose electrons to form cations (M → Mⁿ⁺ + ne⁻)	Gain electrons to form anions (X + ne⁻ → Xⁿ⁻)

The solution was aqua regia (royal water).

Composition: Conc. HCl + Conc. HNO₃ in 3:1 ratio

How it worked:
1. Gold ornaments often have copper/silver impurities mixed in.
2. Aqua regia dissolves gold (neither acid alone can):
Au + 4H⁺ + NO₃⁻ + 4Cl⁻ → AuCl₄⁻ + NO + 2H₂O
3. The outer dull layer (impurities + tarnish) dissolved, making bangles shine.
4. But pure gold also dissolved, reducing weight drastically.

Alternative possibility: Strong cyanide solution (also dissolves gold).

Copper is preferred over steel for hot water tanks because:

1. Corrosion resistance: Copper forms protective basic copper carbonate layer, while steel (iron) rusts easily in presence of water and oxygen.
2. Better heat conductor: Copper conducts heat 8 times better than iron, heating water faster and more evenly.
3. Durability: Copper tanks last longer; steel would require frequent replacement due to rusting.
4. Non-reactivity: Copper doesn't react with hot water; iron reacts with steam to form Fe₃O₄ + H₂.
5. Bacterial resistance: Copper has antimicrobial properties.

Note: Modern tanks sometimes use stainless steel (alloy with Cr, Ni) or glass-lined steel.

(i) Liquid at room temperature: Mercury (Hg)
(ii) Can be cut with knife: Sodium (Na), Potassium (K), Lithium (Li) – alkali metals
(iii) Best conductor of heat: Silver (Ag) [Copper is second best]
(iv) Poor conductor of heat: Lead (Pb), Mercury (Hg)

Additional facts:
• Gallium (Ga) and Caesium (Cs) melt in hand (low melting point).
• Diamond (non-metal) is best conductor of heat among non-metals.

Malleable: Property of metals that allows them to be hammered or rolled into thin sheets without breaking.
• Example: Gold (most malleable) – 1g can be hammered into 1m² sheet
• Application: Making aluminum foil, gold leaf, silver foil

Ductile: Property of metals that allows them to be drawn into thin wires without breaking.
• Example: Gold (most ductile) – 1g can be drawn into 2km long wire
• Application: Making copper wires, steel cables, electrical wires

Non-metals are generally brittle (non-malleable) and non-ductile.

Sodium is kept immersed in kerosene because it is highly reactive with:

1. Oxygen: Catches fire spontaneously in air
4Na + O₂ → 2Na₂O (violent reaction)

2. Water: Reacts violently producing hydrogen which ignites
2Na + 2H₂O → 2NaOH + H₂ + heat

3. Moisture: Even atmospheric moisture can cause reaction

Kerosene: Doesn't react with sodium, prevents contact with air/moisture.
Alternative: Mineral oil or paraffin oil.

Reactivity order: Zn > Fe > Cu > Ag

Analysis:
• Metal displaces another only if it is more reactive.
• A: Displaces Cu & Ag → More reactive than Cu & Ag, but not Fe or Zn.
• B: Displaces Fe & Ag → More reactive than Fe & Ag, but not Cu or Zn.
• C & D: No reactions → Less reactive than all.

Answers:
(i) Cannot determine most reactive from given data (none displaced Zn).
(ii) No reaction (B doesn't displace Cu from table).
(iii) Reactivity order: B > A > C = D
(B displaces Fe; A displaces Cu; C&D displace none)

Displacement occurs when a more reactive metal reduces the oxide of a less reactive metal.

Reactivity series: Mg > Zn > Cu

Possible combinations:
• Mg + ZnO → Displacement (Mg more reactive than Zn)
Mg + ZnO → MgO + Zn

• Mg + CuO → Displacement (Mg more reactive than Cu)
2Mg + CuO → 2MgO + Cu

• Zn + CuO → Displacement (Zn more reactive than Cu)
Zn + CuO → ZnO + Cu

• Others (Zn + ZnO, Cu + CuO, Cu + ZnO, etc.): No displacement

Note: This is similar to thermite reaction: Fe₂O₃ + 2Al → 2Fe + Al₂O₃

Metals that do not corrode easily are:

1. Gold (Au) and Platinum (Pt):
• Noble metals, least reactive
• Don't react with oxygen, water, acids (except aqua regia)
• Used in jewellery, electronic components

2. Silver (Ag):
• Low reactivity, but tarnishes slowly with sulphur compounds
• Forms black Ag₂S layer

3. Aluminium (Al):
• Reactive but forms protective Al₂O₃ layer
• Self-protecting against further corrosion

4. Stainless steel (Fe-Cr-Ni alloy):
• Chromium forms Cr₂O₃ protective layer
• Doesn't rust like ordinary iron

5. Titanium (Ti):
• Forms stable oxide layer
• Used in implants, aerospace

Alloys are homogeneous mixtures of two or more metals, or a metal with a non-metal.

Purpose of making alloys:
1. Enhance properties: Hardness, strength, corrosion resistance
2. Lower melting point: Solder (Pb+Sn) melts easily
3. Reduce cost: Mix expensive with cheaper metals
4. Change appearance: Color, lustre

Important alloys:
• Steel: Fe + C (0.1-2%) – Hard, strong
• Stainless steel: Fe + Cr + Ni – Corrosion resistant
• Brass: Cu + Zn – Decorative, musical instruments
• Bronze: Cu + Sn – Statues, medals
• Solder: Pb + Sn – Low melting, welding
• Amalgam: Hg + other metal – Dental fillings

Note: 24-carat gold is pure; 22-carat gold is alloy (Au + Cu/Ag).