அமிலம், மூலம், உப்பு

1. அமிலம் (Acid)

நீர்க்கரைசலில் ஹைட்ரஜன் அயனிகளை (H⁺ அல்லது H₃O⁺) வெளியிடும் சேர்வைகளே அமிலம். ஒரு spoonful of vinegar-ஐ நீரில் கரைத்தால் — CH₃COOH → CH₃COO⁻ + H⁺.

1.1 அமிலங்களின் தனிப்பண்புகள்

புளிப்பான சுவை (taste — careful! மரபு அமிலங்கள் மட்டுமே — strong அமிலம் அதிபடியாகச் சுவைக்கக்கூடாது).
நீலக் litmus தாளை சிவப்பாக மாற்றும்.
உலோகங்களுடன் தாக்கி ஹைட்ரஜன் வாயு வெளியேற்றும்: Zn + 2HCl → ZnCl₂ + H₂↑.
கார்பனேட்டுகளுடன் CO₂ வெளியேற்றும்: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑.
மூலங்களுடன் neutralisation நடைபெற்று உப்பு + நீர் உருவாக்கும்.
pH < 7 (acidic).

1.2 அமிலங்கள் வகைகள் — origin அடிப்படையில்

வகை	உதாரணம்	பயன்பாடு
கனிய அமிலம் (mineral)	HCl, H₂SO₄, HNO₃	தொழிற்சாலை, ஆய்வுகூடம்
இயற்கை / கரிம (organic)	CH₃COOH (vinegar), citric acid (lemon), lactic acid (curd)	உணவு, சமையல்

1.3 வலிமை அடிப்படையில் — வன் / மென்

வன்னமிலம் (strong acid): நீரில் முழுமையாக ionise ஆகும். உதா: HCl, H₂SO₄, HNO₃. HCl(aq) → H⁺(aq) + Cl⁻(aq) — 100% completion.

மென்னமிலம் (weak acid): பகுதியாகவே ionise ஆகும். உதா: CH₃COOH (vinegar), citric acid, carbonic acid (H₂CO₃ in soda). CH₃COOH ⇌ CH₃COO⁻ + H⁺ — equilibrium.

⚠ நினைவில் Strong ≠ concentrated! Strong = degree of ionisation. Concentrated = amount per volume. மிக சிறிய அளவே HCl-ஐ நீரில் கரைத்தாலும் "strong" — fully ionised.

2. மூலம் (Base)

நீர்க்கரைசலில் OH⁻ (hydroxide) அயனிகளை வெளியிடும் சேர்வைகள். நீரில் கரையும் மூலம் = alkali (காரம்).

படம் 7.3 — பொதுவான மூலங்கள்: NaOH, KOH, Milk of Magnesia (Mg(OH)₂). NIE பாடநூல், தரம் 11

2.1 மூலங்களின் தனிப்பண்புகள்

வலுக் கசப்பான சுவை (மீண்டும் strong — taste தவிர்).
வழவழப்பான / soapy touch — அதனாலேயே வீட்டு cleaning agents போலத் தோன்றும்.
சிவப்பு litmus தாளை நீலமாக மாற்றும்.
அமிலத்தோடு neutralisation → salt + water.
pH > 7 (alkaline).

2.2 மூலங்களின் ionisation

NaOH(aq) → Na⁺(aq) + OH⁻(aq) — strong base, full dissociation.

NH₃ + H₂O ⇌ NH₄⁺ + OH⁻ — weak base, partial.

உதாரணங்கள்: NaOH (caustic soda), KOH, Ca(OH)₂ (slaked lime), NH₃ solution.

3. pH அளவுத்திட்டம் (pH Scale)

ஒரு கரைசலின் acid/base nature-ஐ 0-14 scale-ல் அளக்கின்றோம். pH = −log[H⁺].

pH < 7: Acidic. Lower = more acidic. Gastric acid pH ~1.
pH = 7: Neutral. Pure water.
pH > 7: Basic. Higher = more basic. Lye/NaOH ~14.

3.1 சில அன்றாட கரைசல்களின் pH

கரைசல்	pH
இரைப்பை அமிலம்	1-2
எலுமிச்சை சாறு	2-3
vinegar	~3
தக்காளி	4
தோல்	5.5
தூய நீர் / இரத்தம்	7 / 7.4
சோப்பு	9-10
NaOH 1 M	14

3.2 Indicators (காட்டிகள்)

Litmus: Red/blue colour change. Simple — strong/weak distinguish not.
Phenolphthalein: Colourless (acidic + neutral); pink (basic, pH >8).
Methyl orange: Red (acidic); yellow (basic, pH >4.4).
Universal indicator: Mix of dyes → rainbow colour matching pH chart.
pH paper: Universal indicator impregnated paper.
pH meter: Electronic, highest accuracy.

4. நடுநிலையாக்கம் (Neutralisation)

அமிலம் + மூலம் reaction → உப்பு + நீர். Both acid + base ஒன்றை ஒன்றை counter செய்வதால் "நடுநிலை" reach ஆகின்றது.

HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)

Net ionic equation: H⁺ + OH⁻ → H₂O. அனைத்து neutralisation-களின் அடிப்படை.

4.1 அன்றாட உதாரணங்கள்

இரப்பை புண் சிகிச்சை (antacids): Mg(OH)₂ / Al(OH)₃ tablet → HCl-ஐ neutralise → பயனற்ற salt. பாதிக்கப்பட்ட stomach lining heal.
தேனீ கடி: தேனீ formic acid (மென்னமிலம்) inject. Sodium bicarbonate / soap solution (mild base) application → neutralise → pain relief.
Wasp (குளவி) கடி: Wasp venom alkaline → vinegar / lemon juice (mild acid) → relief.
மண்ணில் pH adjustment: Acidic soil → சுண்ணாம்பு (Ca(OH)₂) add → pH raise. Basic soil → ammonium sulfate fertilizer.
தந்த சுத்தம்: Bacteria-உற்பத்தி lactic acid enamel-ஐ erode. Toothpaste (mild base) → neutralise + remineralise.

5. உப்புகள் (Salts)

Acid-ன் H⁺-ஐ ஒரு metal ion-ஆல் replace செய்தபோது formed compound = salt. Acid-base neutralisation = standard formation method.

படம் 7.5 — Copper sulphate (CuSO₄·5H₂O) — blue crystalline salt. NIE பாடநூல், தரம் 11

5.1 முக்கிய உப்புகள்

உப்பு	பெயர்	பயன்பாடு
NaCl	சமையல் உப்பு	சமையல், food preservation
NaHCO₃	Baking soda	பேக்கிங், antacid
Na₂CO₃	Washing soda	தோய்த்தல், glass making
CaSO₄·2H₂O	Gypsum	Plaster of Paris (model casts)
CuSO₄·5H₂O	Blue vitriol	Fungicide, electroplating
KNO₃	Saltpetre	Fertilizer, explosives
NH₄NO₃	Ammonium nitrate	Fertilizer, explosives

5.2 உப்புகளின் வகைகள் — pH அடிப்படை

Neutral salt: Strong acid + Strong base. e.g., NaCl, KNO₃. pH ~7.
Acidic salt: Strong acid + Weak base. e.g., NH₄Cl. pH < 7.
Basic salt: Weak acid + Strong base. e.g., Na₂CO₃, NaHCO₃. pH > 7.

5.3 Water of crystallisation

Crystal structure-ல் fix-ஆகச் சேர்ந்த water molecules. e.g., CuSO₄·5H₂O (5 water molecules per formula unit), Na₂CO₃·10H₂O (washing soda decahydrate). Heat-ஆல் வெளிவந்தால் anhydrous form-ஆக மாறும். அத்தோடு color-ம் மாறக்கூடும் (blue CuSO₄·5H₂O → white anhydrous CuSO₄).

படம் 7.6 — Crystallized salt — pattern + symmetry. NIE பாடநூல், தரம் 11

6. பயன்பாடுகள் சுருக்கம்

HCl — household cleaning (toilet bowl), metal cleaning, batteries.
H₂SO₄ — car batteries, fertilizers, paper, detergents (\"king of chemicals\").
HNO₃ — fertilizers (ammonium nitrate), explosives (TNT), dyes.
NaOH — soap, paper, textiles.
Ca(OH)₂ — construction (mortar), acidic soil correction.
NaCl — food, road de-icing, chemical industry (chlor-alkali).
NaHCO₃ — baking, antacids, fire extinguishers.

✅ விரைவுச் சோதனை

முக்கியக் கருத்துக்களை உறுதிப்படுத்துங்கள். தவறான விடைகள் உங்கள் தவறுக் குறிப்பேட்டில் சேமிக்கப்படும்.

🖊 கட்டுரை வினாக்கள் (பகுதி II)

பரீட்சை வடிவில் கட்டமைப்பு வினாக்கள். முதலில் நீங்களே எழுதுங்கள்; பின்னர் மாதிரி விடையைத் திறந்து சரிபாருங்கள்.

1. (அ) அமிலம் + மூலம் வரையறை + 4 பண்புகள். (4) (ஆ) Strong vs Weak acid difference + examples. (4) (இ) Strong VS Concentrated — same? (2) (10 புள்ளி)

2. pH scale — concept + range + உதாரண கரைசல்களின் pH (5+). pH<7, =7, >7 கரைசல்களின் hydrogen ion concentrations + acid/base classification. (10 புள்ளி)

3. நடுநிலையாக்கம் (neutralisation) — definition + general equation + ionic equation. 5 அன்றாட உதாரணங்கள் — antacid, bee sting, soil pH, toothpaste, agricultural lime. (10 புள்ளி)

விடைத் திட்டம் — சேர்க்க வேண்டிய புள்ளிகள்:

Acid + base → salt + water.
H⁺ + OH⁻ → H₂O.
Exothermic.
Antacid for heartburn.
Bee sting (acid).
Soil pH correction.
Tooth enamel.
Wasp sting (alkaline).

Neutralisation Definition:
An acid reacts with a base to produce salt + water — the H⁺ from acid and OH⁻ from base combine to form water, while the cation (from base) + anion (from acid) form the salt.

General equation:
Acid + Base → Salt + Water

Specific example:
HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)

Net ionic equation:
H⁺(aq) + OH⁻(aq) → H₂O(l)
This is the universal essence of all acid-base neutralisations — spectator ions (Na⁺, Cl⁻) don't change.

Energetics: Always EXOTHERMIC. For strong acid + strong base ≈ 57 kJ/mol heat released. Test tube warms.

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5 Everyday Applications:

(1) Antacids for heartburn / gastric ulcer:
Irregular meals + spicy food + stress → excess HCl secretion → burning sensation.
Antacids contain Mg(OH)₂ (Milk of Magnesia), Al(OH)₃, or CaCO₃.
Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O.
Stomach acid neutralised → pain relief. Long-term — PPI (proton pump inhibitors) preferred.

(2) Bee sting first aid:
Bee venom contains formic acid (HCOOH) + other compounds → acidic.
Apply mild base — sodium bicarbonate (baking soda) paste or soap solution.
Neutralises acid → reduces pain/swelling.
Note: Wasp sting is alkaline → apply mild acid (vinegar, lemon) instead.

(3) Agricultural soil pH correction:
Many Sri Lankan plantation soils (tea, rubber, coconut) acidic due to high rainfall + organic matter decomposition.
Apply quicklime/slaked lime (CaO / Ca(OH)₂) to raise pH.
Ca(OH)₂ + H⁺ → Ca²⁺ + H₂O. Soil neutralised, nutrient availability improves.
For alkaline soils (less common), use ammonium sulphate or sulphur.

(4) Tooth decay prevention:
Mouth bacteria ferment sugar → produce lactic acid → erodes tooth enamel (hydroxyapatite) below pH 5.5.
Toothpaste contains mild base (calcium carbonate, sodium bicarbonate) + fluoride.
Base neutralises acid; fluoride strengthens enamel.
Brushing 2× daily essential.

(5) Factory wastewater treatment:
Many industries discharge acidic or alkaline effluent → would damage rivers, kill fish.
Wastewater plants neutralise — acidic effluent + lime; alkaline + sulphuric acid.
pH 6-8 final → safe discharge.
Similar logic for acid rain damage mitigation.

Bonus — Stinging plants (Kahambiliya / nettle):
Contain formic acid in stinging hairs → burning sensation on contact.
Apply mild base (soap, baking soda paste) → relief. Same principle as bee sting.

4. உப்புகள் (Salts) — formation + classification (neutral/acidic/basic) + 6 முக்கிய உப்புகளும் அவற்றின் பயன்பாடுகளும். (10 புள்ளி)

விடைத் திட்டம் — சேர்க்க வேண்டிய புள்ளிகள்:

Salt = ionic product of acid+base.
Classification by parent acid/base strength.
NaCl, NaHCO₃, Na₂CO₃, CaSO₄, CuSO₄, KNO₃ etc.
Daily uses.

Salt Formation:
Neutralisation reaction primary route:
Acid + Base → Salt + Water
The H⁺ of acid replaced by cation of base.
Example: HCl + NaOH → NaCl + H₂O
H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O

Other routes:
• Acid + Metal: 2HCl + Zn → ZnCl₂ + H₂
• Acid + Carbonate: 2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂
• Acid + Metal oxide: 2HCl + CuO → CuCl₂ + H₂O

Classification by pH of solution:

(1) Neutral salt (pH ~7):
Strong acid + Strong base → neutral salt. e.g., NaCl, KNO₃, KCl. No hydrolysis in water.

(2) Acidic salt (pH < 7):
Strong acid + Weak base → acidic salt. e.g., NH₄Cl, FeCl₃. Cation hydrolyses:
NH₄⁺ + H₂O ⇌ NH₃ + H₃O⁺ → acidic.

(3) Basic salt (pH > 7):
Weak acid + Strong base → basic salt. e.g., Na₂CO₃, CH₃COONa, NaHCO₃. Anion hydrolyses:
CH₃COO⁻ + H₂O ⇌ CH₃COOH + OH⁻ → basic.

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6 Important Salts + Uses:

(1) Sodium chloride (NaCl) — Table salt:
• Source: Sea evaporation, rock salt mining.
• Uses: Food seasoning + preservation (osmotic dehydration of microbes). Industrial chlor-alkali process — electrolysis produces Cl₂ + NaOH + H₂. Road de-icing in cold countries.
• Sri Lankan context: Eastern coastal salt pans (Hambantota, Mannar) traditional industry.

(2) Sodium bicarbonate (NaHCO₃) — Baking soda:
• Uses: Baking — heat decomposes → CO₂ + Na₂CO₃ + H₂O; CO₂ leavens dough. Antacid. Fire extinguishers (releases CO₂ smothering flame). Cleaning paste. Toothpaste. Bee sting first aid.

(3) Sodium carbonate (Na₂CO₃·10H₂O) — Washing soda:
• Uses: Laundry — softens hard water (precipitates Ca²⁺, Mg²⁺), removes grease. Glass manufacturing — Na₂CO₃ + SiO₂ + CaCO₃ → soda-lime glass. Paper, soap industry.

(4) Calcium sulphate (CaSO₄·2H₂O) — Gypsum / Plaster of Paris:
• POP: CaSO₄·½H₂O obtained by heating gypsum to 150°C.
• Uses: Plaster casts for broken bones. Wall plastering. Decorative mouldings, statues. Cement additive. Blackboard chalk.

(5) Copper sulphate (CuSO₄·5H₂O) — Blue vitriol:
• Properties: Distinctive blue crystals due to hydrated Cu²⁺. Anhydrous form white.
• Uses: Fungicide (Bordeaux mixture in vineyards). Algicide in ponds. Electroplating. Lab chemical tests.

(6) Potassium nitrate (KNO₃) — Saltpetre:
• Uses: NPK fertilizer (K + N source). Gunpowder (75% KNO₃ + 15% C + 10% S). Food preservation (curing). Fireworks oxidiser.

Bonus (7): Ammonium nitrate (NH₄NO₃):
• Uses: High-N fertilizer (~35% N). Industrial explosives. Instant cold packs (endothermic dissolution).
• Highly regulated due to terrorism misuse history.

Water of Crystallisation:
Many salts crystallise with water molecules locked in their lattice — e.g., CuSO₄·5H₂O, Na₂CO₃·10H₂O, CaSO₄·2H₂O. Heating drives water out → anhydrous form. Often colour change accompanies (blue CuSO₄·5H₂O → white anhydrous CuSO₄).

5. Indicators (காட்டிகள்) — 5 types விளக்குக. Each one's behavior + when to use + advantage/limitation. Endpoint detection in titration concept. (10 புள்ளி)

விடைத் திட்டம் — சேர்க்க வேண்டிய புள்ளிகள்:

Litmus, phenolphthalein, methyl orange, universal, pH meter.
Colour changes + pH ranges.
Use cases.
Titration endpoint principle.

Indicators overview:
Acid-base indicators = weak organic acids/bases whose protonated + deprotonated forms have different colours. Colour change occurs over narrow pH range.

5 common indicators:

(1) Litmus:
• Source: Lichens extract.
• Behaviour: Red in acid; blue in base. Change ~pH 5-8.
• Use: Simple acid/base distinction. Litmus paper (red, blue, or neutral).
• Limitation: Cannot distinguish strong/weak. Wide transition range.
• Best for: Quick lab tests, classroom demos.

(2) Phenolphthalein:
• Behaviour: Colourless in acid (and neutral); pink in base (pH > 8.3).
• Use: Titration endpoint for strong acid + strong base + strong acid + weak base titrations (endpoint pH around 7-8).
• Advantage: Sharp colour transition. Easy to see.
• Limitation: Doesn't work in basic side titrations.

(3) Methyl orange:
• Behaviour: Red below pH 3.1; orange around 3.5; yellow above pH 4.4.
• Use: Titration endpoint for strong acid + weak base (e.g., HCl + NH₃, endpoint pH ~4).
• Limitation: Doesn't work for weak acid titrations.

(4) Universal Indicator:
• Composition: Mixture of several dyes (methyl red, bromothymol blue, thymol blue, phenolphthalein, etc.).
• Behaviour: Continuous colour spectrum:
- pH 1-3: Red
- pH 4-6: Orange-yellow
- pH 7: Green
- pH 8-10: Blue
- pH 11-14: Purple
• Use: Estimate pH of unknown solution by matching to chart (±1 accuracy).
• Form: Solution or impregnated pH paper.
• Limitation: Less precise than meter.

(5) pH Meter (electronic):
• Principle: Glass electrode measures voltage proportional to [H⁺]. Display ±0.01 pH.
• Use: Quantitative pH measurement in research, hospital labs, industry, aquaculture, soil testing.
• Advantage: Highest accuracy.
• Limitation: Expensive, requires calibration, electrode care.

Specialty indicators (brief):
• Bromothymol blue: yellow (acid) → blue (base), transition pH 6-7.
• Methyl red: red (acid) → yellow (base), transition pH 4-6.
• Natural indicators: red cabbage juice (red→purple→green→yellow as pH increases), turmeric (yellow→red at pH 7+), hibiscus.

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Titration Endpoint Concept:

Titration = volumetric analysis to determine unknown concentration of acid or base.

Setup:
• Burette: Standard (known concentration) titrant.
• Pipette + conical flask: Unknown (analyte) volume measured exactly.
• Indicator added to flask.
• Titrant added drop-by-drop until colour change → endpoint.

Endpoint: Point where indicator changes colour — approximately matches the equivalence point (where moles acid = moles base reacted).

Indicator selection rule:
• Strong acid + Strong base → use phenolphthalein OR methyl orange (sharp pH jump at equivalence, both work).
• Weak acid + Strong base → phenolphthalein (equivalence pH ~8-9).
• Strong acid + Weak base → methyl orange (equivalence pH ~4-5).
• Weak acid + Weak base → NOT recommended (no sharp transition; use pH meter).

Calculation:
Molarity × Volume of acid (acidic H⁺ count) = Molarity × Volume of base (basic OH⁻ count).
From this, unknown concentration determined.

Real-world applications:
• Water quality testing (alkalinity, acidity).
• Vinegar/lemon juice strength determination.
• Pharmaceutical quality control.
• Wine/beverage analysis.
• Soil + agricultural analysis.

6. Acids, bases, salts ஒவ்வொன்றின் முக்கிய தொழிற்சாலை + வீட்டு பயன்பாடுகளை — H₂SO₄ ("king of chemicals"), NaOH, NaCl, NaHCO₃, CuSO₄, NH₄NO₃ — ஐந்து-ஆறு உதாரணங்களில் விளக்குக. (10 புள்ளி)

விடைத் திட்டம் — சேர்க்க வேண்டிய புள்ளிகள்:

Each one's key industrial use.
Daily/household uses.
Production methods briefly.
Safety considerations.

(1) Sulphuric acid (H₂SO₄) — "King of Chemicals":
Why "king"? Most produced chemical worldwide. Industrial output ≈ economic indicator.
Production: Contact process — S → SO₂ → SO₃ (V₂O₅ catalyst) → H₂SO₄ (absorbed in H₂SO₄, then diluted).
Main uses:
• Fertilizers (~60%): Ammonium sulphate, superphosphate.
• Petroleum refining — alkylation, octane improvement.
• Lead-acid car batteries — electrolyte.
• Paper, textiles, dyes.
• Drain cleaner at high concentration.
Safety: Severe burns + dehydration. Always dilute by adding acid to water (never reverse).

(2) Sodium hydroxide (NaOH) — Caustic soda:
Production: Chlor-alkali electrolysis of brine (NaCl solution).
Main uses:
• Soap manufacturing — saponification (NaOH + fat → soap + glycerol).
• Paper — pulping wood (Kraft process).
• Textiles — mercerising cotton (stronger, shinier).
• Aluminium production — Bayer process (dissolves bauxite).
• Drain cleaner — dissolves hair, grease.
Safety: Severe chemical burns. Soapy slippery feel = danger signal. Eye flush copiously.

(3) Sodium chloride (NaCl):
Sources: Sea evaporation (Sri Lankan salt pans), rock salt mining.
Main uses:
• Food seasoning — daily essential.
• Preservation — fish drying, meat curing (osmotic dehydration kills microbes). Pre-refrigeration era ESSENTIAL.
• Industrial chemistry — feedstock for NaOH, Cl₂, HCl, Na₂CO₃, Na metal production.
• Road de-icing (cold countries) — lowers freezing point.
• Animal feed supplement.
Health note: Excess (>5 g/day) → hypertension, cardiovascular risk.

(4) Sodium bicarbonate (NaHCO₃) — Baking soda:
Source: Solvay process from NaCl + CO₂ + NH₃.
Main uses:
• Baking — heat decomposes: 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂. CO₂ leavens dough.
• Antacid — neutralises stomach acid (mild, fast-acting).
• Fire extinguishers — heat releases CO₂ smothering flame.
• Cleaning paste — mild abrasive, deodoriser.
• Toothpaste — mild base + abrasive.
• Insect bite relief (acid stings).

(5) Copper sulphate (CuSO₄·5H₂O) — Blue vitriol:
Properties: Brilliant blue crystals (hydrated Cu²⁺). Anhydrous form = white powder.
Main uses:
• Bordeaux mixture — fungicide spray for grape vineyards, potato blight.
• Algicide in swimming pools + reservoirs.
• Electroplating — Cu²⁺ deposits on cathode.
• Textile mordant — dye fixing.
• Lab test — Fehling's solution component.

(6) Ammonium nitrate (NH₄NO₃):
Production: NH₃ + HNO₃.
Main uses:
• Fertilizer — high N content (~35%), rapid plant uptake. Critical for green revolution agriculture.
• ANFO explosives — mining, quarrying, construction.
• Instant cold packs — endothermic dissolution.
Safety/regulation: 2020 Beirut explosion (2750 tonnes stored unsafely). Strictly regulated worldwide.

(7) Calcium hydroxide / Slaked lime — Ca(OH)₂):
Production: CaO + H₂O → Ca(OH)₂ + heat.
Uses:
• Construction — mortar, plaster, whitewash.
• Water treatment — pH adjustment, softening.
• Agricultural lime — acidic soil correction.
• Sewage treatment — clarification + sulphide removal.
• Betel chewing in South Asia (with areca nut, traditional).

Common theme: Acids, bases, salts each have indispensable industrial AND household roles. Modern life essentially built on chemistry of these three categories.

7. Acid rain (அமில மழை) — formation chemistry + environmental damage + mitigation. Sri Lankan-context impacts. (10 புள்ளி)

விடைத் திட்டம் — சேர்க்க வேண்டிய புள்ளிகள்:

SO₂ + NOₓ from combustion.
React with water → H₂SO₄ + HNO₃.
Forest, lake, structure damage.
Mitigation: catalytic converters, scrubbers, energy transition.
Sri Lanka coal plant + vehicle issues.

Acid Rain — Definition:
Rainwater with pH < 5.6 (natural rain pH ~5.6 from atmospheric CO₂ forming weak carbonic acid). Below this = anthropogenic pollutant-induced.

Formation Chemistry:

(1) SO₂ source: Coal combustion (sulphur impurity), oil burning, volcanic eruptions, metal smelting. Sulphuric acid:
• 2SO₂ + O₂ → 2SO₃ (catalysis by dust, UV)
• SO₃ + H₂O → H₂SO₄

(2) NOₓ source: Vehicle engines (high-temperature air N₂ + O₂ → NO), power plants, lightning.
• 2NO + O₂ → 2NO₂
• 3NO₂ + H₂O → 2HNO₃ + NO

Result: Rain pH 4-5 typical in polluted areas; pH 2-3 in extreme cases (similar to lemon juice falling from sky).

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Environmental Damage:

(1) Forest decline:
• Leaf damage (waxy cuticle dissolved).
• Soil acidification → leaching of essential nutrients (Ca, Mg, K).
• Release of toxic Al³⁺ from soil minerals → root damage.
• Weakened trees vulnerable to disease, insects.
• Famous example: Black Forest (Germany), Catskill Mountains (USA) — large dieback events 1970s-80s.

(2) Lake + river acidification:
• Aquatic life intolerant. Fish eggs fail to hatch below pH 5.
• Aluminium dissolved from sediments → gill damage in fish.
• Eventually "dead lakes" — clear blue water but no biodiversity.
• Scandinavian lakes (downwind of UK power plants) — historical example.

(3) Building + monument damage:
• Marble (CaCO₃) + H₂SO₄ → CaSO₄ + H₂O + CO₂.
• Marble + limestone monuments slowly dissolved.
• Taj Mahal (India) — yellowish discolouration partly due to acid rain near coal-burning Mathura refinery.
• Acropolis (Greece) — ancient statues replaced by replicas; originals indoor.
• Modern buildings — steel reinforcement corrosion.

(4) Health effects:
• Acid aerosols irritate respiratory system, worsen asthma.
• Toxic metal leaching into drinking water (lead pipes, copper).
• Crops on acidified soil yield reduction.

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Mitigation strategies:

(1) At source:
• Scrubbers at power plants — flue gas + Ca(OH)₂ slurry → CaSO₄ (gypsum) byproduct. Useful for plaster industry.
• Low-sulphur fuels — coal washing, oil hydrodesulphurisation.
• Catalytic converters in vehicles — convert NOₓ → N₂ + O₂.
• Energy transition — solar, wind, nuclear replacing coal.

(2) Tall stacks (only partial solution):
• Sends pollution further away, not eliminating.
• Cross-border pollution issue (Scandinavia ← UK, Eastern US ← Midwest).

(3) Soil + lake liming:
• Spread limestone (CaCO₃) on affected lakes + forests to neutralise.
• Temporary, expensive measure.

(4) International treaties:
• 1979 Geneva Convention on Long-Range Transboundary Air Pollution.
• Acid rain in developed countries reduced 50%+ since 1990 due to scrubbers + cleaner fuels.

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Sri Lankan context:

Current state: Acid rain not yet severe but rising concern.
• Norochcholai Coal Power Plant (300 MW × 3) — significant SO₂ emitter; scrubbers minimal in early years.
• Vehicle emissions — rapid car/3-wheeler increase + diesel buses → urban NOₓ pollution.
• Cement industry — sulphur in coal substitutes.

Vulnerable areas:
• Central highlands (tea plantations) — already naturally acidic soil + added pollution stress.
• Coastal mangroves — fragile pH balance.
• Historical monuments — Sigiriya, Anuradhapura, Polonnaruwa stone structures.

Sri Lanka measures:
• Catalytic converter requirement for new vehicles (since ~2008).
• Sulphur cap on diesel fuel.
• Renewable energy push (solar, wind farms in Mannar, Hambantota).
• National Environmental Act standards.

Future outlook: Energy transition + electric vehicles + emission control = essential to prevent severe acid rain damage. Climate change action overlap.

Action takeaway: Individual citizens — efficient vehicles, reduced consumption, support green energy policy. Collective action saves landscapes + monuments.

🔥 மீட்டல் மையம்

பரீட்சைக்கு முன் இறுதி ஒரு நிமிடம் — மறக்கக்கூடாதவை மட்டும்.

அமிலம் (Acid): நீரில் H⁺ வெளியிடும். புளிப்பு, நீலம்→சிவப்பு litmus, உலோகத்துடன் H₂, கார்பனேட்டுடன் CO₂, pH<7.
மூலம் (Base): OH⁻ வெளியிடும். கசப்பு, சோப்பு touch, சிவப்பு→நீலம் litmus, pH>7.
Strong acid: HCl, H₂SO₄, HNO₃ — 100% ionise.
Weak acid: CH₃COOH, citric, lactic — partial.
Strong base: NaOH, KOH, Ca(OH)₂.
Weak base: NH₃, Mg(OH)₂.
Strong ≠ Concentrated. Strong = ionisation degree; concentrated = amount.
pH: 0-14. 7=neutral. Each unit = 10× [H⁺] change.
Neutralisation: Acid + Base → Salt + Water. H⁺ + OH⁻ → H₂O.
Indicators: Litmus (red/blue), Phenolphthalein (pink in base), Methyl orange (red→yellow), Universal (full spectrum), pH meter (electronic).
Salt types: Neutral (NaCl), Acidic (NH₄Cl), Basic (Na₂CO₃).
Antacid for heartburn. Bee sting (acid) → base. Wasp sting (base) → acid.
Soil pH: Acidic → lime. Alkaline → sulphate.
Salts: NaCl (food), NaHCO₃ (baking), Na₂CO₃ (washing), CuSO₄·5H₂O (blue, fungicide), CaSO₄·½H₂O (POP), KNO₃ (fertilizer).

அலகின் முதுகெலும்பு — கருத்துக்களும் தொடர்புகளும்.

1. Acid definition: Arrhenius — H⁺ donor in water. Bronsted — proton donor. Lewis — e⁻ pair acceptor.
2. Acid properties (5): Sour taste, blue→red litmus, metal+H₂, carbonate+CO₂, pH<7.
3. Base definition: OH⁻ donor. Alkali = water-soluble base.
4. Base properties: Bitter taste, soapy touch, red→blue litmus, pH>7.
5. Strong acids: HCl, H₂SO₄, HNO₃ (also HBr, HI, HClO₄). 100% ionise.
6. Weak acids: Organic (acetic, citric, lactic), carbonic. Partial ionisation = equilibrium.
7. Strong bases: Group 1 + 2 hydroxides — NaOH, KOH, Ca(OH)₂.
8. Weak bases: NH₃, organic amines, Mg(OH)₂, Al(OH)₃.
9. Strong vs Concentrated: Strong = full ionisation. Concentrated = amount per volume. Dilute strong + concentrated weak possible.
10. pH = −log[H⁺]. Scale 0-14. Each pH unit = 10× concentration change. Pure water pH 7.
11. Examples pH: Gastric 1-2, vinegar 3, blood 7.4, soap 9-10, NaOH 14.
12. Neutralisation: Acid + Base → Salt + Water. Net ionic: H⁺ + OH⁻ → H₂O. Exothermic.
13. Acid + metal: Salt + H₂ gas. Reactivity series above H react. Cu, Ag, Au don't.
14. Acid + carbonate: Salt + H₂O + CO₂. CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂.
15. Indicators: Litmus (broad), phenolphthalein (colourless→pink, pH>8.3), methyl orange (red→yellow, pH 3.1-4.4), universal (rainbow), pH meter.
16. Titration: Burette + pipette + indicator. Endpoint = colour change at equivalence point.
17. Salt types: Strong+strong=neutral (NaCl); strong+weak=acidic (NH₄Cl); weak+strong=basic (Na₂CO₃).
18. Water of crystallisation: CuSO₄·5H₂O (blue, 5 water); heat → anhydrous CuSO₄ (white).
19. Key salts: NaCl food/industry; NaHCO₃ baking/antacid; Na₂CO₃ washing/glass; CaSO₄·½H₂O POP; CuSO₄ fungicide; KNO₃ fertilizer.
20. Real-world applications: Antacid + bee sting + soil pH + tooth decay + acid rain mitigation.
21. Acid rain: SO₂ + NOₓ → H₂SO₄ + HNO₃. Damages forests, lakes, monuments. Mitigation = scrubbers + clean fuels.

பரீட்சைக்கு முந்தின இரவு முழு அலகையும் ஓட்டிப் பார்.

Acid: H⁺ in water. Sour, blue→red litmus, metal+H₂, carbonate+CO₂, pH<7.
Base: OH⁻ in water. Bitter, soapy, red→blue litmus, pH>7.
Strong acids: HCl, H₂SO₄, HNO₃. Full ionisation.
Weak acids: Organic (vinegar, citric, lactic), carbonic.
Strong bases: NaOH, KOH, Ca(OH)₂.
Weak bases: NH₃, antacid hydroxides (safer).
Strong ≠ Concentrated. Don't confuse.
pH = −log[H⁺]. 0-14 scale. Each unit 10×.
Neutralisation: A+B → S+W. H⁺+OH⁻ → H₂O. Always exothermic.
3 acid reactions: (1) + base = salt + water (2) + metal = salt + H₂ (3) + carbonate = salt + water + CO₂.
Indicators: Litmus quick check. Phenolphthalein (colourless/pink, base). Methyl orange (red/yellow, acid). Universal rainbow. pH meter accurate.
Salts: NaCl (food), NaHCO₃ (baking), Na₂CO₃ (washing), CuSO₄·5H₂O (blue, fungicide), POP (CaSO₄·½H₂O), KNO₃ (fertilizer).
Salt pH: Strong+strong=neutral. Strong acid+weak base=acidic. Weak acid+strong base=basic.
Daily applications: Antacid → acid stomach. Bee sting (acid) → base. Acidic soil → lime. Wasp sting (base) → vinegar.
Water of crystallisation: CuSO₄·5H₂O. Heat → white anhydrous. Water back → blue.
⚠ Common traps: Concentrated ≠ strong. Vinegar=acetic acid (weak even concentrated). Bicarbonate is base, not acid despite \"hydrogen\" name.
⚠ Safety: Acid to water (AAW). Never water to concentrated acid (explosive boiling).
⭐ Memorise: Neutralisation = exothermic, releases ~57 kJ/mol (strong+strong). Net ionic always H⁺+OH⁻=H₂O.
📋 Glossary: அமிலம்=acid; மூலம்=base; உப்பு=salt; நடுநிலையாக்கம்=neutralisation; வன்னமிலம்=strong acid; மென்னமிலம்=weak acid; pH அளவுத்திட்டம்=pH scale; காட்டி=indicator.