Classification of Acids

Classification of Acids

• Acids are classified based on their sources and basicity.

Sources of Acids

• Organic Acids: Derived from plants and contain carbon.
  • Examples:
    • Oxalic acid (COOH)₂
    • Acetic acid (CH₃COOH)
    • Formic acid (HCOOH)
  • Often weak and do not fully ionize in solution.
  • Sources of organic acids include vinegar (Acetic Acid) and citrus fruits (Citric Acid).
• Inorganic Acids (Mineral Acids): Obtained from minerals and do not contain carbon (with an exception like carbonic acid H₂CO₃).
  • Examples:
    • Hydrochloric acid (HCl)
    • Sulphuric acid (H₂SO₄)
    • Nitric acid (HNO₃)
    • Phosphoric acid (H₃PO₄)
  • These are strong acids, ionizing completely in solution, producing high concentrations of hydronium ions (H₃O+).

Basicity of Acids

• Defined by the number of hydronium ions (H₃O+) produced when an acid ionizes in water.
• Monobasic Acids: Yield one hydronium ion per molecule.
  • Example: HCl
• Dibasic Acids: Yield two hydronium ions.
  • Example: H₂SO₄
• Tribasic Acids: Yield three hydronium ions.
  • Example: H₃PO₄
• Basicity depends on ionizable hydrogen atoms, not just the total hydrogen count.

Acid Concentration and Strength

• Concentration refers to the amount of acid in a solution, influencing its use and safety in handling.
• A concentrated acid contains minimal water, while a dilute acid has significantly more water than acid.
• Diluting an acid requires adding acid to water gradually, never the reverse due to exothermic reactions which can lead to splattering.
• Strength of an Acid: Measured by the concentration of hydronium ions it produces.
  • Stronger acids have higher degrees of ionization (α).
  • Degree of ionization greater than 30% indicates a strong acid, while less signifies a weak acid.

Preparation of Acids

• Acids can be synthesized from non-metals, binary acids, through water reaction, or oxidation processes.

Properties of Acids

• Physical Properties:
  • Sour taste and corrosive nature, particularly in mineral acids.
  • State varies, with examples of solid (boric acid) and liquid (sulphuric acid) acids.
• Effects on Skin:
  • All mineral acids can cause burns and blisters.
  • Specific acids produce characteristic color changes on skin.
• Indicator Color Change:
  • Litmus turns red in acidic solutions, indicating the acidic nature of the solution.

Chemical Reactions

• Reaction with Active Metals:
  • Acids react with active metals, producing metallic salts and hydrogen gas.
• Neutralization of Bases:
  • Acids react with bases to form salt and water.
• Decomposition of Carbonates:
  • Acids react with carbonates and bicarbonates, liberating carbon dioxide.

General Uses of Some Acids

• Boric acid: Eye-wash and antiseptic.
• Citric acid: Vitamin C preparation.
• Acetic acid: Cooking and vinegar.
• Nitric acid: Manufacturing explosives.

Bases

• A base is typically a metallic hydroxide or ammonium hydroxide that reacts with hydronium ions in water.
• Strong Bases: Fully dissociate in solution, e.g. NaOH and KOH.
• Weak Bases: Partially dissociate, e.g. NH₄OH.

Acidity of Bases

• Defined by the number of hydroxyl ions (OH⁻) produced per molecule when dissolved in water.

Preparation of Bases

• Bases can be produced from metals, hydroxides, or through double decomposition.

Properties of Bases

• Physical Properties: Sharp, bitter taste; change color of indicators.
• Chemical Properties: Often form soapy substances and serve as strong electrolytes.