In-depth Notes on Acids

Topic Overview: Acids, Bases, and Salts

Definitions and General Concepts

• Definition of an Acid:
  • Acids are defined as substances that can donate H⁺ ions (protons) to bases, forming salts and water.
  • Proton Donor: An acid is thus referred to as a proton donor.

Common Acids and Their Uses

• Sulfuric Acid (H₂SO₄):
  • Known as battery acid.
• Nitric Acid (HNO₃):
  • Used in making fertilizers and explosives.
• Phosphoric Acid (H₃PO₄):
  • Used as food flavoring.
• Hydrochloric Acid (HCl):
  • Found in stomach acid.
• Acetic Acid (CH₃COOH):
  • Commonly found in vinegar.
• Carbonic Acid (H₂CO₃):
  • Present in carbonated water.

Ionization of Acids in Water

• When an acid is added to water, it ionizes to produce hydrogen ions (H⁺) and negative anions.
• The H⁺ ions associate with polar water molecules to form hydronium ions (H₃O⁺).

Properties of Aqueous Acids

• Common Characteristics:
  • Sour taste.
  • Change blue litmus paper to red.
  • pH value less than 7.
  • Corrosive nature.
  • Conduct electricity as electrolytes.

Chemical Reactions of Aqueous Acids

1. With Reactive Metals:
   • Reactivity produces salt and hydrogen gas (effervescence).
   • Reaction is exothermic.
2. With Metal Carbonates and Bicarbonates:
   • Produces salt, carbon dioxide, and water (effervescence from CO₂).
3. With Bases (Neutralization Reactions):
   • Produces salt and water; also exothermic.

Classification of Acids

• Based on Composition:
  • Inorganic Acids: Do not contain carbon (e.g., HCl, HNO₃).
  • Organic Acids: Contain the carboxyl group (-COOH) (e.g., acetic acid, citric acid).
• Basicity:
  • Monobasic: 1 H⁺ ion (e.g., HCl).
  • Dibasic: 2 H⁺ ions (e.g., H₂SO₄).
  • Tribasic: 3 H⁺ ions (e.g., H₃PO₄).
• Degree of Ionization:
  • Strong Acids: Fully ionized (e.g., HCl).
  • Weak Acids: Partially ionized (e.g., CH₃COOH).
• Concentration:
  • Dilute: High water content (e.g., HCl at 0.01 mol/dm³).
  • Concentrated: Low water content (e.g., HCl at 12 mol/dm³).

Acid Anhydrides

• Definition: A compound that reacts with water to form an acid.
• Examples:
  • Carbon dioxide (CO₂)
  • Sulfur dioxide (SO₂)
  • Sulfur trioxide (SO₃)
  • Nitrogen dioxide (NO₂)

Acids in Living Systems

• Hydrochloric Acid: Found in gastric juices.
• Ascorbic Acid (Vitamin C): Present in citrus fruits and vegetables.
• Citric Acid: Found in citrus fruits like limes and oranges.
• Methanoic Acid: Present in the venom of bee and ant stings.
• Lactic Acid: Produced in muscles during anaerobic respiration and found in yogurt.
• Ethanoic Acid: Found in vinegar.