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CA05 — Metals & Non-Metals

✈ Chemistry – CA05  ·  AFCAT General Awareness AFCAT Level ★ High Priority

Metals and non-metals form the two broad categories of elements, each with distinct physical and chemical properties. AFCAT tests the reactivity series, alloy compositions, and extraction methods. These are high-frequency, pure-recall questions.

📌 AFCAT Focus: Reactivity series order (K>Na>Ca>Mg>Al>Zn>Fe>Ni>Sn>Pb>Cu>Hg>Ag>Au); graphite = only non-metal that conducts electricity; galvanising = zinc coating on iron; brass = Cu+Zn (NOT tin); bronze = Cu+Sn; rusting needs both O₂ AND H₂O.

1. Physical Properties Comparison

Fig. 1 — Metals vs Non-Metals: Physical Properties at a Glance
METALS vs NON-METALS — Physical Properties Property METALS NON-METALS Physical state Solid at room temperature Solid, liquid or gas (Hg = liquid metal exception) Lustre Shiny / lustrous Dull (iodine exception) Malleability Malleable (beaten into sheets) Brittle (break on hammering) Conductivity Good conductors heat & electricity Poor conductors (graphite = exception!) Ductility Ductile (drawn into wires) Non-ductile

2. Reactivity Series & Alloys

Fig. 2 — Reactivity Series and Extraction Method
REACTIVITY SERIES — Most to Least Reactive Most Least HIGHLY REACTIVE → Extracted by ELECTROLYSIS only K > Na > Ca > Mg > Al React vigorously with cold water; K and Na stored under kerosene. Cannot be extracted by chemical reduction. Aluminium: electrolysis of molten alumina (Al₂O₃) — Hall-Héroult process. MODERATELY REACTIVE → Extracted by REDUCTION (with C or CO) Zn > Fe > Ni > Sn > Pb React with dilute acids; not cold water. Extracted by roasting their ores and reducing with coke (carbon). Iron extracted in blast furnace: Fe₂O₃ + 3CO → 2Fe + 3CO₂ — — — H₂ (Hydrogen) — — — LEAST REACTIVE → Found FREE in nature or extracted by HEATING alone Cu > Hg > Ag > Au > Pt Gold, silver and platinum found as native metals (free elements). Copper extracted by heating Cu₂S in air.

3. Important Alloys

AlloyCompositionKey Property & Use SteelFe + C (0.2–2%)Strong, hard; construction, railways, machinery Stainless SteelFe + Cr (18%) + Ni (8%)Rust-resistant; kitchen utensils, surgical tools BrassCu + ZnMusical instruments, decorative items, coins BronzeCu + SnStatues, coins, bearings, bells DuraluminAl + Cu + Mg + MnAircraft construction (light and strong) SolderPb + Sn (60:40)Joining electrical wires; low melting point German SilverCu + Zn + NiUtensils, jewellery (contains NO actual silver!)

4. Rust Prevention Methods

Rusting requires both oxygen and moisture. Remove either, and rusting stops. AFCAT tests this as a direct question: "Which method prevents rusting by acting as a sacrificial anode?"

Fig. 3 — Five Methods to Prevent Rusting of Iron
FIVE METHODS TO PREVENT RUSTING Method How it works Example / Use 1. Painting / Coating Creates a physical barrier between iron surface and air / moisture. Iron bridges, railings, ships 2. Oiling / Greasing Oil / grease film prevents oxygen and water from reaching surface. Machine parts, tools, gun barrels 3. Alloying (Stainless steel) Chromium in stainless steel forms a self-healing Cr₂O₃ passive layer. Cutlery, surgical tools, aircraft 4. Galvanising (Zn coating) Zinc is more reactive; it corrodes first, protecting iron beneath. Water pipes, roofing sheets, buckets 5. Cathodic Protection A more reactive metal (Mg or Zn) is attached; it acts as sacrificial anode. Ship hulls, underground pipelines (AFCAT favourite!)
💡 Cathodic Protection — The AFCAT Trap: In cathodic protection, a block of a more reactive metal (usually magnesium or zinc) is bolted to the iron structure. This block — the sacrificial anode — corrodes preferentially because it is higher in the reactivity series. The iron becomes the cathode and is protected. Used on ship hulls (zinc blocks), offshore oil rigs, and buried pipelines. It is the most technically tested rust prevention concept in AFCAT.

📝 AFCAT PYQs — Metals & Non-Metals

Q1. Which non-metal conducts electricity? AFCAT PYQ
(a) Diamond(b) Sulfur(c) Graphite(d) Phosphorus
✔ Answer: (c) Graphite
Graphite is the only non-metal that is a good conductor of electricity. Each carbon atom in graphite bonds to 3 others in hexagonal layers, leaving one delocalised free electron per atom to carry charge. Diamond (same element, different structure) is an excellent insulator. Graphite is used as electrodes in batteries and electrolytic cells.
Q2. Brass is an alloy of: AFCAT PYQ
(a) Copper and Tin(b) Copper and Zinc(c) Iron and Carbon(d) Aluminium and Copper
✔ Answer: (b) Copper and Zinc
Brass = Copper + Zinc. Used for musical instruments, decorative items, coins. Common confusion: Bronze = Copper + Tin (used for statues, bells). The Brass/Bronze confusion is a direct AFCAT trap question. Mnemonic: BrAss = with Zinc (Z like the letter at the end of alpha-bZet). Bronze = with tiN.
Q3. Galvanising protects iron by coating it with: AFCAT PYQ
(a) Copper(b) Tin(c) Zinc(d) Nickel
✔ Answer: (c) Zinc
Galvanising coats iron with zinc to prevent rusting. Zinc is more reactive than iron (in the reactivity series Zn > Fe), so it acts as a sacrificial anode — corroding preferentially even if the coating is scratched. Used in galvanised iron pipes, roofing sheets, and buckets. Tin plating (food cans) protects by creating a barrier — but once scratched, iron corrodes faster than tin.

🧠 Quick Memory Chart — CA05

⚗ Reactivity Series
  • K>Na>Ca>Mg>Al → Electrolysis
  • Zn>Fe>Ni>Sn>Pb → Reduction
  • Cu>Hg>Ag>Au → Free / Heating
  • K and Na: stored under kerosene
  • Fe displaces Cu (Fe > Cu in series)
⚛ Key Alloys
  • Brass: Cu + Zn (musical instruments)
  • Bronze: Cu + Sn (statues, bells)
  • Steel: Fe + C; Stainless: Fe+Cr+Ni
  • Duralumin: Al+Cu+Mg (aircraft)
  • German silver: has NO silver!
🚨 Key Traps
  • Graphite: only non-metal that conducts
  • Rusting: needs O₂ AND H₂O (both!)
  • Galvanising: Zn coating on Fe
  • Hg = only liquid metal at room temp
  • Na: stored under kerosene (reacts with water)

📝 Practice Exercise

E1. Duralumin is used in aircraft because it is:
(a) Very cheap(b) Light and strong(c) Very hard(d) Magnetic
E2. Which metal is stored under kerosene?
(a) Gold(b) Iron(c) Sodium(d) Copper
E3. Bronze (used for statues) is an alloy of:
(a) Copper and Zinc(b) Copper and Tin(c) Iron and Carbon(d) Lead and Tin
Answers:
E1 → (b) Light and strong [Al-based; ideal for aircraft where weight is critical]  |  E2 → (c) Sodium [reacts explosively with water and moisture in air; kerosene keeps it isolated]  |  E3 → (b) Copper and Tin [Bronze = Cu+Sn; Brass = Cu+Zn; this distinction is tested directly]
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