Metals and Non-Metals: Reactivity Series, Extraction and Corrosion Facts for SSC & Railways
Quick Answer: The reactivity series of metals, from most to least reactive, is K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au. Rule of thumb: highly reactive metals (K–Al) are extracted by electrolysis, moderately reactive ones (Zn–Pb) by roasting/calcination followed by reduction, and least reactive ones (Hg–Ag) by heating alone. Corrosion is the slow eating away of metals by air, moisture or chemicals — rust is hydrated iron(III) oxide.
- Reactivity Series of Metals: Full Order with Mnemonic
- Why Hydrogen Sits in the Middle: Displacement Reactions Explained
- Reactive vs Least Reactive: How Metals Are Extracted (Flowchart)
- Extraction of Moderately Reactive Metals: Roasting and Calcination
- Thermite Reaction and Reduction with Carbon/Aluminium
- Corrosion: Definition, Rusting Equation and Conditions
- Corrosion Examples for MCQs: Copper, Silver and Aluminium
- Prevention of Corrosion: Galvanisation, Alloying and Painting
- Properties of Metals vs Non-Metals: Quick Fact Table
- Metals and Non-Metals: Previous Year Questions Snapshot
- One-Page Revision Points
- Frequently Asked Questions
- Q: What is the easiest mnemonic to remember the reactivity series?
- Q: Why is gold found in free state in nature?
- Q: What are the two conditions required for rusting of iron?
- Q: What is galvanisation?
- Q: Why is aluminium extracted by electrolysis and not by carbon reduction?
- Related reading
Reactivity Series of Metals: Full Order with Mnemonic
The reactivity series (also called the activity series) arranges metals in decreasing order of their tendency to lose electrons and form positive ions. Potassium is the most reactive common metal; gold is the least. This single arrangement decides displacement behaviour, extraction method and corrosion tendency — which is why it appears so frequently in SSC CGL, CHSL, MTS, Railway NTPC and Group D papers, as well as CBSE Class 10 Science.
Full order:
K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au
Popular English mnemonic: “Please Stop Calling Me A Zebra In Lead Hotels — Copper Mercury Silver Gold.” A widely used Hindi mnemonic runs: “Kalan Kalium Ke Saath Mange Aluminium Ziladata Faltu Pyar Hui Hai Chhodo Meri Soni Aunty” — mapping to K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Hg, Ag, Au.
Why Hydrogen Sits in the Middle: Displacement Reactions Explained
Hydrogen is placed in the series even though it is a non-metal because metals are routinely compared against it in acid reactions. One-line logic: metals above hydrogen displace hydrogen from dilute acids; metals below hydrogen cannot.
- Zinc + dilute sulphuric acid: Zn + H₂SO₄ → ZnSO₄ + H₂ (gas evolved)
- Iron + dilute hydrochloric acid: Fe + 2HCl → FeCl₂ + H₂
- Copper + dilute HCl: No reaction — copper lies below hydrogen.
The same logic applies to metal-salt displacement: a more reactive metal displaces a less reactive metal from its salt solution. Iron dipped in copper sulphate solution gets coated with red-brown copper (Fe + CuSO₄ → FeSO₄ + Cu), while copper in iron sulphate solution shows no change.
Reactive vs Least Reactive: How Metals Are Extracted (Flowchart)
The reactivity series directly determines the extraction route because the more reactive a metal is, the more stable its compounds are, and the harder its oxide is to reduce.
| Reactivity Band | Metals | Extraction Method |
|---|---|---|
| Highly reactive | K, Na, Ca, Mg, Al | Electrolysis of molten ores/oxides |
| Moderately reactive | Zn, Fe, Pb, Cu | Roasting/calcination followed by reduction with carbon (or aluminium) |
| Least reactive | Hg, Ag, Au | Heating alone (for Hg, Ag); Au found in free/native state |
Flowchart: Identify metal’s position → K–Al: electrolytic reduction → Zn–Pb: concentrate ore → roast/calcine → reduce with carbon → Hg–Ag: heat the sulphide ore alone → Au: occurring native, needs no chemical extraction.
Extraction of Moderately Reactive Metals: Roasting and Calcination
Two classic one-liner favourites for SSC:
- Roasting — heating the ore strongly in excess air; used for sulphide ores. Zinc blende: 2ZnS + 3O₂ → 2ZnO + 2SO₂. The oxide is then reduced with carbon: ZnO + C → Zn + CO.
- Calcination — heating the ore strongly in limited or no air; used for carbonate and hydroxide ores. Calamine: ZnCO₃ → ZnO + CO₂.
Memory hook: Roasting → sulphide ores; Calcination → carbonate ores. For a deeper dive into extraction chemistry, the NCERT Class 10 Science chapter on Metals and Non-Metals (ncert.nic.in/textbook.php) is the authoritative source for exam purposes.
Thermite Reaction and Reduction with Carbon/Aluminium
The thermite reaction is the reduction of a metal oxide by aluminium powder, which is highly exothermic and produces molten metal:
Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + heat
The molten iron produced is used to weld broken railway tracks and cracked machine parts — a classic Railway RRB exam fact. Aluminium is used as a reducing agent because it is more reactive than iron and has a strong affinity for oxygen.
Corrosion: Definition, Rusting Equation and Conditions
Corrosion is the slow eating up of a metal surface by the action of air, moisture or chemicals present in the environment. The most familiar example is the rusting of iron. Chemically, rust is hydrated iron(III) oxide (Fe₂O₃·xH₂O), a brown, flaky deposit that does not stick to the surface and hence exposes fresh metal to further attack.
Conditions for rusting: iron rusts only when both oxygen (air) and moisture are present. In dry air or in boiled water without air, iron does not rust — a standard SSC practical-knowledge question.
Corrosion Examples for MCQs: Copper, Silver and Aluminium
- Copper: develops a green coating of basic copper carbonate [CuCO₃·Cu(OH)₂] on exposure to moist air containing CO₂.
- Silver: develops a black coating of silver sulphide (Ag₂S) due to sulphur compounds in air — why silver ornaments tarnish.
- Aluminium: reacts with oxygen to form a thin, sticky, protective layer of aluminium oxide (Al₂O₃) that prevents further corrosion — the reason aluminium utensils stay corrosion-resistant.
Prevention of Corrosion: Galvanisation, Alloying and Painting
- Galvanisation: coating iron or steel with a thin layer of zinc; used for water pipes, roofing sheets and wire fences. Zinc corrodes sacrificially, protecting iron even if the coating scratches.
- Electroplating: depositing a layer of tin, nickel or chromium on the metal surface.
- Alloying: mixing a metal with other metals/non-metals to improve resistance — stainless steel (iron + chromium + nickel) does not rust; brass (copper + zinc) and bronze (copper + tin) resist corrosion better than pure copper.
- Painting, greasing and oiling: simple barrier methods that keep air and moisture away from the metal surface.
Properties of Metals vs Non-Metals: Quick Fact Table
| Property | Metals | Non-Metals |
|---|---|---|
| Lustre | Shiny (lustrous) | Dull (except iodine, graphite) |
| State at room temperature | Solid (except mercury — liquid) | Solid, liquid (bromine) or gas |
| Malleability | Can be hammered into sheets | Brittle; break into powder |
| Ductility | Drawn into wires (gold most ductile) | Non-ductile |
| Conductivity | Good conductors of heat and electricity | Poor conductors (except graphite) |
| Sonority | Sonorous — produce ringing sound | Non-sonorous |
Metals and Non-Metals: Previous Year Questions Snapshot
- Which metal is used in the thermite reaction for welding railway tracks? — Aluminium (reduces Fe₂O₃ to molten iron).
- Rust is chemically: — Hydrated iron(III) oxide (Fe₂O₃·xH₂O).
- The green coating on copper objects is: — Basic copper carbonate.
- Which metal is extracted by electrolysis of its molten oxide? — Aluminium.
- Which of the following metals does not react with dilute HCl: Zn, Fe, Mg, Cu? — Copper (below hydrogen in the series).
One-Page Revision Points
- Series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
- Above H → displace hydrogen from dilute acids; below H → no reaction.
- Extraction: K–Al electrolysis; Zn–Pb roasting/calcination + carbon reduction; Hg–Ag heating alone; Au native.
- Roasting = sulphide ores (excess air); Calcination = carbonate ores (limited air).
- Thermite: Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + heat — railway track welding.
- Rust = Fe₂O₃·xH₂O; needs both air (oxygen) and moisture.
- Copper → green carbonate; silver → black sulphide; aluminium → protective oxide.
- Prevention: galvanisation (zinc coating), alloying (stainless steel, brass), painting/oiling.
- Only mercury is liquid metal; only bromine is liquid non-metal; graphite conducts though non-metal.
Frequently Asked Questions
Q: What is the easiest mnemonic to remember the reactivity series?
“Please Stop Calling Me A Zebra In Lead Hotels — Copper Mercury Silver Gold” maps directly to K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Hg, Ag, Au.
Q: Why is gold found in free state in nature?
Gold is the least reactive metal in the series, so it does not readily combine with oxygen, sulphur or other elements and occurs in its native (free) state.
Q: What are the two conditions required for rusting of iron?
Presence of both oxygen (air) and moisture. If either is absent — for example, iron in boiled water sealed from air — rusting does not occur.
Q: What is galvanisation?
Coating iron or steel with a thin layer of zinc to prevent rusting. It is commonly used on water pipes, roofing sheets and fencing wires.
Q: Why is aluminium extracted by electrolysis and not by carbon reduction?
Aluminium is more reactive than carbon can reduce at feasible temperatures — its bond with oxygen in Al₂O₃ is very strong — so the oxide is reduced electrolytically (electrolysis of molten alumina) instead of by heating with carbon.
Related reading
- SSC CGL Answer Key Watch: The Week-One Protocol for Checking, Challenging and Reading the Result
- Time, Speed & Distance Shortcuts: Relative Speed, Trains and Boats Formulas with Solved SSC PYQs
Quick revision
- Zinc + dilute sulphuric acid: Zn + H₂SO₄ → ZnSO₄ + H₂ (gas evolved)
- Iron + dilute hydrochloric acid: Fe + 2HCl → FeCl₂ + H₂
- Copper + dilute HCl: No reaction — copper lies below hydrogen.
- Roasting: — heating the ore strongly in excess air; used for sulphide ores.
- Calcination: — heating the ore strongly in limited or no air; used for carbonate and hydroxide ores. Calamine: ZnCO₃ → ZnO + CO₂.
- Copper: develops a green coating of basic copper carbonate [CuCO₃·Cu(OH)₂] on exposure to moist air containing CO₂.
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