7.4 The Formula and Structure of Common Acids

Relevance in daily life:
- Occur in kitchens, laundry, gardening, swimming pools, and human body.

Definition: Corrosive substances that react with solids, effectively 'eating' them away.
Characteristics:
  - Sour taste.
  - Some acids can be dangerously corrosive (e.g., sulfuric acid from car batteries).
  - Pain caused by acids in ant and bee stings.
  - Safe and pleasant acids in fruits and vinegar.
Types of Acids:
  - Strong Acids: Fully react with other substances.
    - Examples:
      - Hydrochloric acid (HCl)
      - Sulfuric acid (H2SO4)
      - Nitric acid (HNO3)
  - Weak Acids: Do not fully react with other substances.
    - Examples:
      - Ethanoic acid (CH3COOH)
      - Carbonic acid (H2CO3)
      - Phosphoric acid (H3PO4).
Etymology of Acid:
- Latin word 'acidus' meaning 'sour'.

Definition: Substances with a bitter taste and slippery or soapy feel to touch.
- Bases vary in corrosiveness; caustic soda (sodium hydroxide) is an example of a very corrosive base.
**Uses of Bases:
- Cleaning agents:
- Found in soap, shampoo, toothpaste, dishwashing liquid, and cloudy ammonia.
Classification of Bases:
  - Alkalis: Bases that dissolve in water.
  - Strength Measurement:
    - Measured using the pH scale (0 to 14).
    - pH Levels:
      - Below 7 indicates acids; the lower the pH, the stronger the acid.
      - Above 7 indicates bases; the higher the pH, the stronger the base.
      - pH of 7 is neutral.
Types of Bases:
  - Strong Bases: Fully react with other substances.
    - Examples:
      - Potassium hydroxide (KOH)
      - Sodium hydroxide (NaOH)
      - Barium hydroxide (Ba(OH)2)
  - Weak Bases: Do not fully react with other substances.
    - Examples:
      - Ammonia (NH3)
      - Calcium carbonate (CaCO3)
      - Sodium carbonate (Na2CO3).

Definition: Reaction between an acid and a base, producing water and a salt.
Importance:
  - Useful for relieving pain from indigestion or insect stings.
  - Adjusting soil pH suitable for specific plants.
  - Applications in cooking and sanitation in pools and spas.
Process of Neutralisation:
- Involves the addition of a base to an acid to neutralize its effect, and vice versa.
Modeling Neutralisation Reactions:
- Known as double displacement reactions where acid (AC) and base (BD) swap partners to form salt (AB) and water (H2O).
Example Reaction in Garden:
- Ant or bee sting (formic acid) can be neutralized with soap or baking soda.
- Wasp sting (contains a base) can be treated with vinegar (acid).
Soil Neutralisation:
- Acidic soils can be neutralized with lime (a base).
- Basic soils can be neutralized with ammonium sulfate, a weak acid salt.
**Example of Neutralisation Reaction: **
  - Acid + Base → Water + Salt.
  - Example:
    - Hydrochloric acid + Sodium hydroxide → Water + Sodium chloride
    - $HCl + NaOH → H2O + NaCl$

Activity: pH at Home:
- Explore locations of various cleaning products on the pH scale to understand acidic and basic characteristics.

Ant and Bee Stings:
  - Painful due to acid in ant stings and base in wasp stings.
  - Correct neutraliser should be applied based on type of sting.
  - Lime can help adjust soil pH, enabling better plant growth.

Questions to assess understanding of acid-base reactions and neutralisation processes.