Study of Acids, Bases and Salts Short notes and Selected PYQs

Acid: A substance that liberates hydrogen ions (H⁺) when dissolved in water.
Taste: Sour taste (e.g., lemon contains citric acid, vinegar contains acetic acid).
pH Range: pH < 7. Strong acids have pH 0-3, weak acids 3-7.
Indicators: Turn blue litmus red, methyl orange red, phenolphthalein colorless.
Classification by Strength: Strong acids (HCl, H₂SO₄, HNO₃) - complete ionization. Weak acids (CH₃COOH, H₂CO₃) - partial ionization.
Classification by Basicity: Monobasic (HCl, HNO₃), Dibasic (H₂SO₄, H₂CO₃), Tribasic (H₃PO₄). Basicity = number of replaceable H⁺ ions.
Common Acids: Hydrochloric acid (HCl), Sulphuric acid (H₂SO₄), Nitric acid (HNO₃), Acetic acid (CH₃COOH), Carbonic acid (H₂CO₃).

Base: A substance that liberates hydroxide ions (OH⁻) when dissolved in water.
Alkali: A water-soluble base (e.g., NaOH, KOH, NH₄OH). All alkalis are bases, but not all bases are alkalis.
Taste: Bitter taste, soapy feel.
pH Range: pH > 7. Strong bases have pH 11-14, weak bases 7-11.
Indicators: Turn red litmus blue, methyl orange yellow, phenolphthalein pink.
Classification by Acidity: Monoacidic (NaOH, KOH), Diacidic (Ca(OH)₂, Mg(OH)₂), Triacidic (Al(OH)₃). Acidity = number of replaceable OH⁻ ions.
Common Bases: Sodium hydroxide (NaOH) - caustic soda, Potassium hydroxide (KOH) - caustic potash, Calcium hydroxide (Ca(OH)₂) - slaked lime.

Neutralization: Reaction between acid and base to form salt and water. Acid + Base → Salt + Water.
Example: HCl + NaOH → NaCl + H₂O. H⁺ + OH⁻ → H₂O (ionic equation).
Salt: Ionic compound formed by replacement of H⁺ of acid by metal or NH₄⁺ ion.
Types of Salts: Normal salt (all H⁺ replaced - NaCl), Acid salt (partial replacement - NaHCO₃), Basic salt (partial OH⁻ replacement - Zn(OH)Cl).
Salt Properties: Crystalline solids, conduct electricity in molten/aqueous state, have high melting points.
pH of Salts: Strong acid + Strong base = Neutral (pH 7). Strong acid + Weak base = Acidic (pH < 7). Weak acid + Strong base = Basic (pH > 7).

pH Scale: Measure of acidity or basicity, ranges from 0 to 14.
pH 7: Neutral (pure water). pH < 7: Acidic. pH > 7: Basic/Alkaline.
pH Formula: pH = -log[H⁺]. Lower pH = higher H⁺ concentration = more acidic.
Universal Indicator: Shows different colors at different pH values (red = acidic, green = neutral, blue/purple = basic).
Litmus: Natural indicator from lichens. Red in acid, blue in base, purple in neutral.
Phenolphthalein: Colorless in acid/neutral, pink in base.
Methyl Orange: Red in acid, yellow in base/neutral.

Acid + Metal: → Salt + Hydrogen gas. Example: Zn + 2HCl → ZnCl₂ + H₂↑
Acid + Metal Oxide: → Salt + Water. Example: CuO + H₂SO₄ → CuSO₄ + H₂O
Acid + Metal Carbonate: → Salt + Water + CO₂. Example: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑
Acid + Metal Hydrogen Carbonate: → Salt + Water + CO₂. Example: NaHCO₃ + HCl → NaCl + H₂O + CO₂↑
Base + Acid: → Salt + Water (Neutralization). Example: NaOH + HCl → NaCl + H₂O
Base + Ammonium Salt: → Salt + Ammonia + Water. Example: NH₄Cl + NaOH → NaCl + NH₃↑ + H₂O

Uses of H₂SO₄: In batteries, fertilizers, petroleum refining, detergents.
Uses of HCl: In cleaning, pickling of metals, laboratory reagent.
Uses of NaOH: Soap making, paper industry, petroleum refining, cleaning agents.
Water of Crystallization: Fixed number of water molecules chemically combined in crystalline salt. Example: CuSO₄·5H₂O (blue vitriol).
Efflorescence: Loss of water of crystallization when exposed to air. Example: Na₂CO₃·10H₂O loses water and forms powder.
Deliquescence: Absorption of moisture from air to form solution. Example: NaOH, CaCl₂ are deliquescent.
Hygroscopic: Absorbs moisture but doesn't form solution. Example: Conc. H₂SO₄ is hygroscopic (used as drying agent).

Study of Acids, Bases and Salts