Cheat Sheet — Acids, Bases & Salts

⚖️ Acids vs Bases — Quick Comparison

Property	Acids	Bases
Ion produced	H⁺ (H₃O⁺)	OH⁻
pH	Less than 7	Greater than 7
Taste	Sour	Bitter
Blue litmus	Turns red	No change
Red litmus	No change	Turns blue
Examples	HCl, H₂SO₄, CH₃COOH	NaOH, Ca(OH)₂, NH₄OH
Reaction product	Acid + Base → Salt + Water (Neutralisation)

📊 pH Scale at a Glance

0123456 7891011121314

Acidic (0–6)
pH 1 → Gastric acid
pH 2.5 → Vinegar
pH 3 → Lemon juice
pH 6 → Milk

Neutral (7)
pH 7 → Pure water
pH 7 → NaCl solution
[H⁺] = [OH⁻]

Basic (8–14)
pH 7.4 → Blood
pH 10 → Milk of magnesia
pH 11 → Ammonia
pH 13 → NaOH

🔥 Key Reactions of Acids

Acid + Metal

Zn + H₂SO₄ → ZnSO₄ + H₂↑
(pop sound with burning splint)

Acid + Metal Carbonate

Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂↑
(lime water turns milky)

Acid + Metal Bicarbonate

NaHCO₃ + HCl → NaCl + H₂O + CO₂↑

Acid + Metal Oxide

CuO + H₂SO₄ → CuSO₄ + H₂O
(black → blue)

Neutralisation

HCl + NaOH → NaCl + H₂O + Heat

🧪 Indicators

IndicatorIn AcidIn Base

Litmus (Red)No changeTurns blue

Litmus (Blue)Turns redNo change

PhenolphthaleinColourlessPink/Red

Methyl orangeRed/PinkYellow

UniversalRed→YellowGreen→Violet

Universal indicator shows full pH range in colour.

🧂 Important Salts — Names, Formulas & Uses

Common Salt

NaCl

Neutral

Food, preservation, electrolysis (chlor-alkali process)

Washing Soda

Na₂CO₃·10H₂O

Basic

Glass/soap/paper industry, water softening, removes grease

Baking Soda

NaHCO₃

Weakly Basic

Baking powder, antacid for acidity, fire extinguisher

Bleaching Powder

Ca(OCl)Cl

Basic

Disinfecting water, bleaching cotton and linen

Plaster of Paris

CaSO₄·½H₂O

Neutral

Casts/moulds, chalk, dental models — sets hard with water

Gypsum

CaSO₄·2H₂O

Neutral

Heated at 373K → Plaster of Paris; used in cement

Blue Vitriol

CuSO₄·5H₂O

Acidic

Fungicide, electroplating; turns white (anhydrous) on heating

⚡ Chlor-Alkali Process

2NaCl(aq) + 2H₂O →
2NaOH + Cl₂↑ + H₂↑

Anode (+) → Cl₂ gas (yellow-green)

Cathode (−) → H₂ gas (colourless)

Solution → NaOH remains

Cl₂ → bleaching powder, PVC
H₂ → fuel, Haber process
NaOH → soap, detergents

💧 Water of Crystallisation

Fixed water molecules in crystal formula unit.

CuSO₄·5H₂O → CuSO₄ + 5H₂O
(Blue) heat⟶ (White powder)

Na₂CO₃·10H₂O → Na₂CO₃ + 10H₂O
(Washing soda → Anhydrous)

CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O
(Gypsum 373K → Plaster of Paris)

Adding water to anhydrous CuSO₄ reverses it → blue again ✓

🎯 Exam Tips & Memory Tricks

ABHS Rule

Acid + Base → Salt + H₂O (neutralisation is always exothermic)

Pop vs Milky

H₂ → pop sound | CO₂ → lime water milky | Cl₂ → bleaches damp litmus

Blue→White→Blue

CuSO₄·5H₂O heated → white. Add water → blue again. Water of crystallisation!

All Alkalis = Bases

NOT all bases = alkalis. Cu(OH)₂ = base, insoluble ∴ NOT alkali.

pH each unit = ×10

pH 4 has 10× more H⁺ than pH 5. pH 1 has 1000× more H⁺ than pH 4.

Natural Acids Mnemonic

Lemon Citric, Vinegar Acetic, Ant Formic, Curd Lactic, Tomato Oxalic

POP sets hard

CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O (Gypsum). Expands slightly — good for casts.

Chlor-Alkali mnemonic

ClAO: Cl₂ at Anode, H₂ at cathOde, NaOH in sOlution