🧪 Chemistry — Elements and Compounds
1. Metals
PROPERTIES OF METALS
- Good conductors of heat and electricity (Ag best, Cu next)
- Malleable: Can be beaten into sheets (Au, Ag most malleable)
- Ductile: Can be drawn into wires (Au, Ag most ductile)
- Hard: Except Na, K (can be cut with knife)
- Solids at room temperature: Except Hg (liquid), Cs and Ga (liquid above 30°C)
- Electropositive: Form positive ions
- Basic oxides: Except ZnO, Al₂O₃ (amphoteric)
ALKALI METALS AND THEIR COMPOUNDS
- Stored under kerosene or liquid paraffin
- Sodium (Na): Prepared by electrolysis of NaCl + CaCl₂ (Down's cell)
- NaOH (Caustic soda): Used in soap, dyes, artificial silk, refining of bauxite
- NaHCO₃ (Baking soda): Used in fire extinguishers, effervescent drinks, fruit salts
- Na₂CO₃·10H₂O (Washing soda): Used in glass, soap, softening hard water
- Na₂SO₄·10H₂O (Glauber's salt): Used as purgative
- Na₂S₂O₃·5H₂O (Hypo): Used in photography as fixing agent
ALKALINE EARTH METALS
- CaO (Quick lime): Used in glass, cement, bleaching powder
- Ca(OH)₂ (Slaked lime): Used in softening hard water
- CaSO₄·2H₂O (Gypsum): Used in plaster of Paris, building plaster
- Plaster of Paris (CaSO₄·½H₂O): Used in statues, toys, dental/medical applications
- CaC₂ (Calcium carbide): Used in preparation of acetylene
2. Important Metals
ALUMINIUM (Al)
- Third most abundant element in Earth's crust
- Extracted from bauxite (Al₂O₃·2H₂O)
- Used in: Utensils, aircraft, automobiles, thermite welding
- Ruby: Red due to Cr in Al₂O₃; Sapphire: Blue due to Fe and Ti
- Emerald: Green due to Ca/Cr in Al₂SiO₃
IRON (Fe)
- Extracted from haematite ore
- Cast iron: 2.5-4% carbon (most impure)
- Wrought iron: 0.12-0.5% carbon (purest form)
- Stainless steel: Fe + Cr + Ni
- Haemoglobin: Contains Fe(II)
- Ferric chloride (FeCl₃): Used as styptic to stop bleeding
COPPER, SILVER & GOLD (Coinage Metals)
- Not affected by air (except Cu → green film)
- Silver bromide (AgBr): Used in photography
- AgNO₃ (Lunar caustic): Used in marking inks, hair dyes
- CuSO₄ + lime (Bordeaux mixture): Fungicide
- CuSO₄·5H₂O (Blue vitriol): Nila thotha
- Purity of gold: 24 carats = pure gold
ZINC (Zn)
- Used in galvanisation to prevent rusting of iron
- ZnO (Philosopher's wool): Used in cosmetics, zinc ointment
- ZnSO₄·7H₂O (White vitriol): Used as mordant in dyeing, eye lotion
MERCURY (Hg)
- Transported in iron containers (does not form alloy with Fe)
- HgCl₂ (Corrosive sublimate): Poisonous; antidote is egg white
- HgS (Vermilion): Used in Ayurvedic medicine as Makardhwaja
3. Metallurgy
BASIC TERMS
- Minerals: Natural substances containing metals and impurities
- Ores: Minerals from which metal can be extracted profitably
- Gangue/Matrix: Impurities associated with ore
IMPORTANT ORES
| Metal | Ore | Chemical Composition |
|---|---|---|
| Aluminium | Bauxite | Al₂O₃·2H₂O |
| Iron | Haematite | Fe₂O₃ |
| Copper | Copper pyrites | CuFeS₂ |
| Zinc | Zinc blende | ZnS |
| Mercury | Cinnabar | HgS |
| Silver | Silver glance | Ag₂S |
IMPORTANT ALLOYS
| Alloy | Composition | Uses |
|---|---|---|
| Solder | Sn + Pb | Soldering |
| Bronze | Cu + Sn | Utensils, statues, coins |
| Brass | Cu + Zn | Utensils, tubes |
| Stainless steel | Fe + Cr + Ni | Utensils, bicycle parts |
| German silver | Cu + Zn + Ni | Utensils, resistance wires |
| Duralumin | Al + Cu + Mg + Mn | Aeroplanes, automobile parts |
4. Non-Metals
CARBON (C)
- Allotropes: Diamond, Graphite, Fullerene (C₆₀), Graphene
- Diamond: Purest form, hardest, bad conductor of electricity
- Graphite: Good conductor, used as dry lubricant, moderator in nuclear reactor
- Fullerene (C₆₀): Soccer ball shape, superconducting at 10-40K
- Graphene: One-atom-thick, 2D material, strong, conductive; used in touchscreens, LCD, LED
- Carbon monoxide (CO): Poisonous, forms carboxyhaemoglobin (200x more stable than oxyhaemoglobin)
- CO₂ (Dry ice): Solid CO₂; used in refrigerators as Drikold
NITROGEN (N₂)
- 79% of atmosphere by volume
- Essential constituent of proteins
- Haber's Process: N₂ + H₂ → NH₃ (catalyst: Fe, promoter: Mo)
- Nitrogen fixation: By lightning and nitrogen-fixing bacteria (Rhizobium in legumes)
OXYGEN (O₂) & OZONE (O₃)
- 21% of atmosphere by volume
- Generated by photosynthesis
- Ozone layer: Absorbs UV rays; depleted by CFCs
- Ozone used as: Bleaching agent, germicide, disinfectant
SULPHUR (S)
- Allotropes: Rhombic (most stable), Monoclinic, Plastic
- Sulphuric acid (H₂SO₄): King of chemicals; manufactured by Contact Process (V₂O₅ catalyst)
- Used in: Fertilisers, explosives, drugs, petroleum refining
- Hypo (Na₂S₂O₃·5H₂O): Fixing agent in photography
5. Halogens and Noble Gases
HALOGENS
- Chlorine (Cl₂): Yellow-green gas; bleaching agent; used in water purification
- Bleaching powder (CaOCl₂): Obtained by passing Cl₂ over dry slaked lime
- Iodine (I₂): Turns starch solution blue; used in treatment of goitre (KI/I₂ solution)
- Oxidising power: F₂ > Cl₂ > Br₂ > I₂
NOBLE GASES
- He: Used in gas-cooled atomic reactors, balloons, deep-sea diving (with O₂)
- Ne: Used in neon discharge lamps and signs
- Ar: Most abundant noble gas in atmosphere; used in electric bulbs (with 15% N₂)
- Kr: Used in high efficiency miner's cap lamps
- Xe: "Stranger gas"; used in high intensity photographic flash tubes
- Rn: Used in ointment for cancer treatment
6. Acids, Bases and Salts
CONCEPTS OF ACIDS AND BASES
- Arrhenius: Acid = H⁺ donor in water; Base = OH⁻ donor in water
- Bronsted-Lowry: Acid = Proton donor; Base = Proton acceptor
- Lewis: Acid = Electron pair acceptor; Base = Electron pair donor
INDICATORS & pH SCALE
- Natural indicators: Litmus, Turmeric, China rose petals
- Synthetic indicators: Methyl orange, Phenolphthalein
- pH scale: 0-14; pH < 7 = Acidic, pH = 7 = Neutral, pH > 7 = Basic
- Human blood pH: 7.36-7.42; change by 0.2 → death
- pH + pOH = 14
TYPES OF SALTS
- Normal salts: NaCl, NaNO₃
- Acidic salts: NaHCO₃, NaHSO₄
- Basic salts: Mg(OH)Cl, Zn(OH)Cl
- Double salts: Mohr's salt [FeSO₄(NH₄)₂SO₄·6H₂O], Potash alum
- Mixed salts: Bleaching powder (CaOCl₂)
SALT HYDROLYSIS
- Strong acid + Strong base: Neutral (NaCl)
- Strong acid + Weak base: Acidic (FeCl₃, CuSO₄)
- Weak acid + Strong base: Basic (Na₂CO₃, CH₃COONa)
- Weak acid + Weak base: Depends on Ka/Kb (CH₃COONH₄ → neutral)
Summary: Elements and Compounds at a Glance
| Topic | Key Point |
|---|---|
| Best Conductor | Silver (Ag) — best conductor of heat and electricity |
| Most Malleable | Gold (Au) and Silver (Ag) |
| Liquid Metals | Mercury (Hg), Caesium (Cs), Gallium (Ga) |
| Stainless Steel | Fe + Cr + Ni |
| Diamond | Purest form of carbon; hardest substance |
| Graphene | 2D material; one-atom-thick; good conductivity |
| pH of Blood | 7.36-7.42 |
KEY TAKEAWAYS FOR UPSC
- Metals: Good conductors, malleable, ductile; Ag best conductor
- Sodium compounds: NaOH (caustic soda), NaHCO₃ (baking soda), Na₂CO₃ (washing soda)
- Plaster of Paris: CaSO₄·½H₂O; used in statues, dental/medical applications
- Alloys: Solder (Sn+Pb), Bronze (Cu+Sn), Brass (Cu+Zn), Stainless steel (Fe+Cr+Ni)
- Diamond: Purest carbon; Graphite: Conductor, lubricant
- Graphene: 2D, strong, conductive; used in touchscreens
- Ozone: Absorbs UV; depleted by CFCs
- Noble gases: He (balloons, diving), Ne (signs), Ar (bulbs)
- pH scale: 0-14; blood pH 7.36-7.42
- Salt hydrolysis: Strong+Weak = Acidic/Basic; Strong+Strong = Neutral
High-Yield Interactive UPSC Quiz (Chemistry — Elements and Compounds)
Q1. Which metal is the best conductor of heat and electricity?
Correct Answer: B. Silver (Ag) is the best conductor of heat and electricity, followed by copper.
Q2. What is the chemical name of baking soda?
Correct Answer: C. Baking soda is sodium bicarbonate (NaHCO₃).
Q3. Stainless steel is an alloy of:
Correct Answer: C. Stainless steel is an alloy of iron (Fe), chromium (Cr), and nickel (Ni).
Q4. Which allotrope of carbon is the hardest substance?
Correct Answer: B. Diamond is the hardest natural substance and the purest form of carbon.
Q5. What is the pH range of human blood?
Correct Answer: B. Human blood has a pH range of 7.36-7.42. A change of 0.2 units can be fatal.
Q6. Which metal is liquid at room temperature?
Correct Answer: C. Mercury (Hg) is the only metal that is liquid at room temperature.
Q7. Which gas is known as "stranger gas"?
Correct Answer: C. Xenon (Xe) is known as "stranger gas" and is used in high-intensity photographic flash tubes.
Q8. The Contact Process is used for manufacturing:
Correct Answer: C. The Contact Process (using V₂O₅ catalyst) is used for manufacturing sulphuric acid.
Q9. Which compound is used as a fixing agent in photography?
Correct Answer: B. Sodium thiosulphate (Hypo) is used as a fixing agent in photography.
Q10. What is the chemical formula of Plaster of Paris?
Correct Answer: B. Plaster of Paris is calcium sulphate hemihydrate (CaSO₄·½H₂O).