Acids and Bases

Introduction to Acids and Bases

Acids

• Definition: Acid is a substance that produces hydrogen ions ($H^+$) when dissolved in water.
  • Not all substances with hydrogen are acids (e.g., water).
• Properties: The hydrogen ions are responsible for the characteristic properties of acids.

Common Acids

• Man-Made Acids:

  • Hydrochloric Acid ($HCl$)
  • Sulphuric Acid ($H2SO4$)
  • Nitric Acid ($HNO_3$)

• Natural Acids:

  • Ethanoic Acid (found in vinegar)

Strong Acids

• Definition: A strong acid completely ionizes in water.
• Examples:
  • Hydrochloric Acid: $HCl(aq)$
  • Sulphuric Acid: $H2SO4(aq)$
  • Nitric Acid: $HNO_3(aq)$

Examples of Acids

Weak Acids

• Definition: A weak acid partially ionizes in water.
• Examples:
  • Acetic Acid: $CH_3COOH(aq)$
  • Citric Acid: $C6H8O_7(aq)$
  • Carbonic Acid: $H2CO3(aq)$

Properties of Acids

• Sour taste
• Conduct electricity when dissolved in water (forming solutions)
• Turn blue litmus paper red
• pH value < 7

Chemical Properties of Acids

1. Reaction with Metals:

   • Acids react with reactive metals to produce a salt and hydrogen gas:
     $ext{Metal} + ext{Acid} <br /> ightarrow ext{Salt} + ext{Hydrogen}$
   • Example:
     $ext{Mg}(s) + ext{H}<em>2SO</em>4(aq) <br /> ightarrow ext{MgSO}<em>4(aq) + ext{H}</em>2(g)$

2. Reaction with Carbonates:

   • Produces salt, carbon dioxide, and water:
     $ext{Acid} + ext{Carbonate} <br /> ightarrow ext{Salt} + ext{Carbon Dioxide} + ext{Water}$
   • Example:
     $ext{Na}<em>2CO</em>3 + ext{HCl} <br /> ightarrow ext{NaCl} + ext{H}<em>2O + ext{CO}</em>2$

3. Reaction with Metal Oxides and Hydroxides:

   • Produces salt and water:
     $ext{Metal Oxide} + ext{Acid} <br /> ightarrow ext{Salt} + ext{Water}$

Role of Water in Acidity

• Acids react in water to break apart into hydrogen ions and salts.
• Acids show their properties only when dissolved in water.

Uses of Acids

• Sulphuric Acid:
  • Used in detergents and car batteries.
• Ethanoic Acid:
  • Used in vinegar for food preservation and adhesives.
• Hydrochloric Acid:
  • Used for cleaning metals and leather processing.

Bases

• Definition: A base is a metal oxide or hydroxide that reacts with an acid.
• Reaction with Acids: $ext{Acid} + ext{Base} ightarrow ext{Salt} + ext{Water}$
  • Also written as: $ext{Acid} + ext{Metal Oxide/Hydroxide} <br /> ightarrow ext{Salt} + ext{Water}$
• Ionic Equation:
  $ext{OH}^- + ext{H}^+ <br /> ightarrow ext{H}_2O(l)$

Common Bases

• Sodium Oxide
• Zinc Oxide
• Copper (II) Oxide
• Magnesium Hydroxide
• Aluminum Hydroxide

Alkalis

• Definition: A soluble base in water.
• Common Examples:
  • Sodium Hydroxide
  • Potassium Hydroxide
  • Calcium Hydroxide
  • Barium Hydroxide
  • Aqueous Ammonia

Properties of Alkalis

• Bitter taste and soapy feel.
• Turn red litmus paper blue.
• pH value > 7.

Chemical Properties of Alkalis

• Produce hydroxide ions when dissolved in water:
  • Example:
    $ext{NaOH} + ext{H}_2O <br /> ightarrow ext{Na}^+ + ext{OH}^-$
• React with ammonium salts to release ammonia gas: $ext{Alkali} + ext{Ammonium Salt} ightarrow ext{Ammonia} + ext{Water} + ext{Salt}$
  • Example:
    $ext{Calcium Hydroxide} + ext{Ammonium Chloride} <br /> ightarrow ext{Calcium Chloride} + ext{Water} + ext{Ammonia}$

Uses of Alkalis

• Ammonia Solution: Window cleaning solutions
• Calcium Oxide: Used to make iron, concrete, cement
• Magnesium Hydroxide: Found in toothpaste and antacids to relieve indigestion.
• Sodium Hydroxide: Used in making soaps and detergents.

pH Indicators

• Universal Indicator pH Scale:
  • pH values range from 1 (Strong Acids) to 14 (Strong Alkalis).
  • Colors:
  • Red: pH 1-3 (Strong Acids)
  • Orange: pH 4-6 (Weak Acids)
  • Green: pH 7 (Neutral)
  • Blue: pH 8-10 (Weak Alkalis)
  • Purple-Violet: pH 11-14 (Strong Alkalis)