Ch 06: Acid, Base & Salt | Exam Fusion Prep

🧪 Chapter At a Glance

🔴 ACID

pH < 7
Sour taste
Blue litmus → Red
Releases H⁺ (Arrhenius)
Proton donor (Brønsted)
Accepts e⁻ pair (Lewis)

🔵 BASE

pH > 7
Bitter taste
Red litmus → Blue
Releases OH⁻ (Arrhenius)
Proton acceptor (Brønsted)
Donates e⁻ pair (Lewis)

Acidic: pH < 7 (25°C)

7
Neutral

Basic: pH > 7 (25°C)

📊 Key Facts — Quick Reference

Aqua Regia

3:1 HCl:HNO₃ (dissolves Au, Pt)

Sørensen

Discoverer of pH concept

7.35–7.45

Normal Blood pH

No fixed ±0.2 rule

No universal fatal-change threshold

🔴 Acids — Concepts & Properties

Arrhenius Concept

Releases H⁺ in aqueous solution

e.g., HCl → H⁺ + Cl⁻ in water | H₂SO₄ → 2H⁺ + SO₄²⁻

Brønsted-Lowry Concept

Proton (H⁺) donor

e.g., HCl, H₂SO₄ donate proton to base

Lewis Concept

Accepts electron pair

Lewis acids: BF₃, AlCl₃ (electron deficient)

Nature: Corrosive
Taste: Sour
Blue litmus → Red litmus
pH < 7
Aqueous solution = Good conductor of electricity

⚗️ Acid Reactions

Acid + Metal → Salt + H₂↑Zn + 2HCl → ZnCl₂ + H₂↑

Acid + Carbonate → Salt + H₂O + CO₂↑CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂↑

Acid + Alkali (Base) → Salt + Water (Neutralisation)HCl + KOH → KCl + H₂O

👑 Aqua Regia

📘 Aqua Regia

Fresh mixture of 3 parts concentrated HCl + 1 part concentrated HNO₃. Called "Royal Water". Dissolves Gold (Au) and Platinum (Pt) — noble metals that resist ordinary acids.

Ratio

3:1 (HCl:HNO₃)

Dissolves

Gold (Au) & Platinum (Pt)

Nature

Must be freshly prepared

⚠️ Exam Trap — Special Acids

HCl (Hydrochloric acid) = helps in digestion of food (stomach acid)
HF (Hydrofluoric acid) = dissolves glass (only acid that does)
Benzoic acid = used in medicine
Glacial acetic acid = 99–100% pure acetic acid (ethanoic acid)
Aqua Regia ratio = 3:1 (HCl:HNO₃) NOT 1:3

🍋 Natural Sources & Uses of Major Acids

Acid	Natural Source	Industrial Formation	Key Uses
Citric Acid	Citrus fruit, lemon, orange, tomato	Fermentation of raw sugar	Food, medicine, cleaning, textile
Acetic Acid	Vinegar and fermented ethanol-containing liquids	Methanol carbonylation (major modern industrial route)	Food acidulant; manufacture of acetate esters and other chemicals
Formic Acid	Ants and stinging nettles	Methanol + CO → methyl formate, followed by hydrolysis	Fruit preservation, antibacterial, leather & rubber
Sulphuric Acid	Acid rain, volcanic activity	Contact process (modern); lead-chamber process (historical)	Rechargeable batteries, medicines, explosives
Nitric Acid	Saltpeter/nitrate salts (historical nitrate source)	Ostwald process: catalytic oxidation of ammonia	Fertilisers, explosives and nitration/chemical manufacture
Benzoic Acid	Some fruits/berries and plant resins	Oxidation of toluene (major industrial route)	Medicine, food preservation
Oxalic Acid	Sorrel tree, spinach, beetroot	From sodium formate	Photography, printing, leather bleaching
Malic Acid	Apple, banana, orange peel, potato, carrot	Hydration of maleic/fumaric acid to produce malic acid	Cosmetics, skin care products

⚠️ Exam Trap — Acid Sources

Formic acid: classically ants and stinging nettles; scorpion venom is not simply formic acid
Citric acid = Lemon, Orange, Tomato
Oxalic acid = Spinach, Beetroot
Acetic acid = Vinegar (glacial acetic = 99–100% pure)
Sulphuric acid (Contact method): catalyst = V₂O₅

🔵 Bases — Concepts & Properties

Arrhenius Concept

Gives OH⁻ ions in aqueous solution

e.g., NaOH → Na⁺ + OH⁻ | KOH → K⁺ + OH⁻

Brønsted-Lowry Concept

Accepts protons (H⁺)

e.g., NH₃, H₂O act as bases by accepting H⁺

Lewis Concept

Donates an electron pair to form a bond; not an oxidation/electron-loss definition

e.g., Cl⁻, F⁻, OH⁻ (electron pair donors)

Taste: Bitter
Red litmus → Blue litmus
pH > 7
Insoluble bases (ZnO, FeO) — react with acids but do NOT have basic properties in water

💊 Uses of Important Bases

Base	Common Name	Key Uses
Ca(OH)₂	Slaked Lime	Whitewashing and neutralising acidic soil
NaOH	Caustic Soda	Soap making, petroleum refining
Mg(OH)₂	Milk of Magnesia	Removing stomach acidity (antacid)
CaO	Quicklime	Cement/steel manufacture, drying and neutralising acidic materials
MgO	Magnesia	Pharmaceuticals, rubber fillers, boilers
KOH	Caustic Potash	Lab reagents, CO₂ & SO₂ absorber

⚠️ Exam Trap — Base Uses

Stomach acidity = Mg(OH)₂ (Milk of Magnesia) — NOT NaOH
Soap making = NaOH (Caustic Soda)
Slaked lime, Ca(OH)₂: whitewashing and acidic-soil treatment
KOH absorbs CO₂ and SO₂ gases in lab

🧂 Salt — Definition & Types

📘 Definition

Product of neutralisation reaction of an acid and a base.
Acid + Base → Salt + Water

HNO₃ + KOH → KNO₃ + H₂OAcid + Base → Salt + Water (Neutralisation)

Type of Salt	Description	Example
Common Salt	Sodium Chloride	NaCl
Acid (hydrogen) salt — composition	Partial neutralisation of a polyprotic acid retains ionisable H; this classification does not by itself determine solution pH	NaHCO₃
Basic Salt	Retains hydroxyl group(s) after incomplete neutralisation of a polyhydroxy base	Mg(OH)Cl
Double Salt	Crystalline combination of two simple salts in a fixed ratio	Alum: K₂SO₄·Al₂(SO₄)₃·24H₂O
Mixed Salt	Contains more than one kind of cation or anion	CaOCl₂ (Bleaching Powder)

💊 Important Salts & Their Uses

Salt	Formula	Common Name	Key Uses
NaCl	NaCl	Common Salt / Table Salt	Food, pickle preservation; making baking soda & NaOH
NaOH	NaOH	Caustic Soda	Soap, detergents, wood pulp (paper), purification of bauxite
Na₂CO₃·10H₂O	Na₂CO₃·10H₂O	Washing Soda	Glass, paper, soap, borax making; treats permanent hardness of water
NaHCO₃	NaHCO₃	Baking Soda	Fire extinguisher; leavening agent in baking; making fried food
Ca(OCl)₂	Ca(OCl)₂	Bleaching Powder	Bleaching textiles/paper, oxidising agent and water disinfection
CaSO₄·½H₂O	CaSO₄·½H₂O	Plaster of Paris (P.O.P.)	Plastering broken bones; chalk, toys, decorative items
C₆H₅COONa	C₆H₅COONa	Sodium Benzoate	Preservative; making jam, tomato sauce

🔬 Important Salt Formulas (Crystalline Salts)

Substance	Formula	Common Name
Epsom Salt	MgSO₄·7H₂O	Magnesium Sulphate heptahydrate
Mohr's Salt	FeSO₄·(NH₄)₂SO₄·6H₂O	Iron Ammonium Sulphate
Alum	K₂SO₄·Al₂(SO₄)₃·24H₂O	Potassium Alum
Blue Vitriol	CuSO₄·5H₂O	Copper Sulphate pentahydrate
White Vitriol	ZnSO₄·7H₂O	Zinc Sulphate heptahydrate

⚠️ Exam Trap — Salt Uses

Baking Soda (NaHCO₃) = fire extinguisher + leavening agent
Washing soda: Na₂CO₃·10H₂O; used to remove permanent water hardness
Bleaching powder: Ca(ClO)₂ in the OP’s current-NCERT convention; actual commercial composition is complex. Traditional CaOCl₂ is treated as mixed salt.
Plaster of Paris = CaSO₄·½H₂O (NOT CaSO₄·2H₂O which is Gypsum)
Blue Vitriol = CuSO₄·5H₂O (Copper sulphate — blue colour)
Epsom salt = MgSO₄·7H₂O (laxative, bath salt)

🎨 Indicators

📘 Definition

Substances used to test acidity or basicity of a solution by changing colour.

Indicator	Colour in Acid	Colour in Base
Litmus	Red	Blue
Phenolphthalein	Colourless	Pink
Methyl Orange	Red	Yellow
Methyl Red	Red	Yellow
Phenol Red	Yellow	Red/Pink

Olfactory Indicators (Smell-based)

Lose smell in Base; Retain smell in Acid

Indicator	In Base	In Acid
Clove Oil	Smell lost ✗	Smell retained ✓
Vanilla	Smell lost ✗	Smell retained ✓
Onion	Smell lost ✗	Smell retained ✓

⚠️ Exam Trap — Indicators

Phenolphthalein: Acid = Colourless; Base = Pink
Methyl Orange: Acid = Red; Base = Yellow
Phenol Red: Acid = Yellow; Base = Red/Pink (opposite of Methyl Orange!)
Olfactory indicators: smell lost in Base, retained in Acid

📊 pH Scale

📘 pH Definition

Sørensen’s logarithmic hydrogen-ion activity scale; “power/potential of hydrogen” is a classroom expansion. Concentration gives a dilute-solution approximation.

pH = −log₁₀a(H⁺) ≈ −log₁₀[H⁺] (dilute solution)Dilute ideal solution: [H⁺] ≈ 10^(−pH) mol L⁻¹; introduced by Sørensen

Acidic: pH < 7 (25°C)

7
Neutral

Basic: pH > 7 (25°C)

Substance	pH Value
Lemon Juice	2.0–2.5
Vinegar	2.4–3.4
Milk (cow)	6.4–6.8
Saliva	6.2–7.6
Neutral (Pure Water)	7.0
Tears	7.0–7.5
Blood Plasma	7.35–7.45
Sea water	7.8–8.4
Beverages	2–4

⚠️ Exam Trap — pH

pH discovered by Sørensen (NOT Arrhenius or Brønsted)
Blood pH = 7.35–7.45 (slightly basic)
Severe blood-pH abnormalities are dangerous; there is no universal ±0.2 = death rule
Lemon pH = 2.0–2.5 (most acidic commonly asked)
Sea water pH = 7.8–8.4 (basic)
Higher pH = more basic; Lower pH = more acidic
pH is not restricted to 0–14; it depends on concentration/activity and does not by itself rank intrinsic acid/base strength

🎯 High-Yield Exam Points

Acid: pH < 7, sour, Blue litmus → Red
Base: pH > 7, bitter, Red litmus → Blue
Arrhenius: acid increases H₃O⁺ in water; base increases OH⁻. Proton donor/acceptor defines Brønsted acid/base.
Brønsted: Acid = proton donor; Base = proton acceptor
Lewis: Acid = accepts e⁻ pair (BF₃, AlCl₃); Base = donates e⁻ pair
Aqua Regia = 3:1 HCl:HNO₃; dissolves Gold & Platinum
HCl = stomach acid (digestion) | HF = dissolves glass
Glacial acetic acid = 99–100% pure acetic acid
Formic acid: ants and stinging nettles
Citric acid in lemon, orange, tomato
Oxalic acid in spinach, beetroot
NaOH = Caustic Soda = soap making, paper (wood pulp)
Mg(OH)₂ = stomach antacid
Baking Soda = NaHCO₃ = fire extinguisher + baking
Washing soda = Na₂CO₃·10H₂O; permanent-hardness treatment
Bleaching Powder = Ca(OCl)₂ = pool cleaning, water disinfection
Plaster of Paris = CaSO₄·½H₂O
Blue Vitriol = CuSO₄·5H₂O | Epsom Salt = MgSO₄·7H₂O
Phenolphthalein: Acid = Colourless; Base = Pink
Methyl Orange: Acid = Red; Base = Yellow
Olfactory indicators: smell lost in Base, retained in Acid
pH = −log₁₀a(H⁺) ≈ −log₁₀[H⁺] for dilute solutions; Sørensen
Normal blood pH ~7.35–7.45; clinical severity depends on the abnormality and context, not a universal ±0.2 rule
Lemon pH = 2.0–2.5 | Sea water pH = 7.8–8.4

📋 Acid vs Base Quick Table

Property	Acid	Base
pH	< 7	> 7
Taste	Sour	Bitter
Litmus	Blue → Red	Red → Blue
Arrhenius	Gives H⁺	Gives OH⁻
Brønsted	Proton donor	Proton acceptor
Lewis	Accepts e⁻ pair	Donates e⁻ pair
Phenolphthalein	Colourless	Pink
Methyl Orange	Red	Yellow

⚠️ Most Common Exam Traps

Aqua Regia = HCl:HNO₃ = 3:1 (NOT 1:3)
HF dissolves glass (NOT HCl)
Phenolphthalein in acid = Colourless (NOT red)
Phenol Red: acid = Yellow (opposite of Methyl Orange)
Olfactory indicators lose smell in Base
POP = CaSO₄·½H₂O (NOT 2H₂O — that's Gypsum)
Washing soda = Na₂CO₃·10H₂O; anhydrous Na₂CO₃ is soda ash; NaHCO₃ is baking soda
Traditional CaOCl₂ is described as mixed salt; distinguish that notation from Ca(ClO)₂ and complex commercial bleaching powder
Lewis ACID accepts e⁻; Lewis BASE donates e⁻
Blood pH is tightly regulated; a fixed ±0.2 fatality rule is incorrect

🧪 Acid, Base & Salt