ACIDS BASES AND SALTS

Acids, Bases, and Salts

Study of Acids, Bases, and Salts

  • Definitions and Properties:

    • Acids: Substances that produce hydronium ions (H₃O⁺) in solution.

    • Bases: Substances that produce hydroxide ions (OH⁻) in solution.

    • Salts: Formed by replacing some or all of the hydrogen ions of an acid with metal or ammonium ions.

  • Testing for Acidity and Alkalinity:

    • Use of litmus paper:

      • Blue litmus turns red in acid.

      • Red litmus turns blue in alkali.

    • pH paper and Universal indicator can also be used to determine acidity or alkalinity.

  • Ionization/Dissociation of Acids, Bases, and Salts:

    • Acids:

      • Example: HCl → H⁺ + Cl⁻

    • Bases:

      • Example: NaOH → Na⁺ + OH⁻

    • Salts:

      • Example: NaCl formed from NaOH + HCl.

Types of Salts

  • Normal Salts: Formed by complete replacement of hydrogen ions.

    • Example: Sodium chloride (NaCl) from HCl.

  • Acid Salts: Formed by partial replacement of hydrogen ions.

    • Example: Sodium hydrogen sulfate (NaHSO₄).

  • Basic Salts: Formed by partial replacement of hydroxyl ions.

  • Double Salts: Contain more than one cation or anion.

  • Complex Salts: Contain complex ions along with simple ions.

General Properties of Salts

  • Deliquescence: Ability to absorb moisture from the air and dissolve in it.

  • Efflorescence: Loss of water of crystallization to become powdery when exposed to dry air.

  • Water of Crystallization: Water molecules associated with crystalline salts.

    • Example: Copper(II) sulfate pentahydrate (CuSO₄•5H₂O).

Chemical Reactions Involving Salts

  • Decomposition reactions involving carbonates, bicarbonates, sulfates, etc., when heated or reacted with acids.

  • Action of Acids:

    • Acids react with carbonates to produce carbon dioxide gas, salt, and water.

    • Example: CaCO₃ + 2 HCl → CaCl₂ + H₂O + CO₂.

Preparation of Salts in the Laboratory

  • Neutralization: Most common method involving the reaction of an acid with a base to produce a salt and water.

    • Example: HCl + NaOH → NaCl + H₂O.

  • Direct Combination: Combining elements directly to form salts.

    • Example: S + O₂ → SO₄.

  • Displacement Reactions: More reactive metals displace less reactive metals from their salts.

    • Example: Zn + CuSO₄ → ZnSO₄ + Cu.

Types of Acids

  • Organic Acids: Contain carbon and generally derived from living organisms.

    • Example: Acetic acid (CH₃COOH).

  • Inorganic Acids: Usually derived from minerals and do not necessarily contain carbon.

    • Example: Sulfuric acid (H₂SO₄).

  • Strength and Concentration:

    • Concentrated Acid: Small amount of water.

    • Diluted Acid: Large amount of water.

    • Acidity depends on concentration of H₃O⁺ ions in solution.

pH Scale

  • Ranges from 0 to 14; 7 is neutral.

  • pH < 7 indicates acidic solutions, pH > 7 indicates alkaline solutions.

  • Importance of pH in biological systems and agricultural practices.

Effects and Reactions of Acids

  • Corrosive Properties: Strong acids can damage skin and materials.

  • Indicators: Change color in response to pH changes (e.g., phenolphthalein, methyl orange).

  • Gas Liberation: Many acid reactions produce gases (e.g., H₂ from metals, CO₂ from carbonates).

Hydrolysis of Salts

  • Salts react with water to form acidic or basic solutions depending on the acid and base from which they are formed.

  • Salts formed from strong acids and weak bases yield acidic solutions.

  • Salts formed from weak acids and strong bases yield basic solutions.

Common Uses of Acids and Bases

  • Boric Acid: Eye wash/antiseptic.

  • Citric Acid: Food preservation.

  • Nitric Acid: Used in explosives.

  • Alkalis: Used in soap making and as neutralizing agents in various applications.