Acid and bases

• Bases


  Substances that can neutralise acids
• Bases


  • NaOH (sodium hydroxide)
  • NaHCO₃ (bicarbonate of soda)
  • CaCO₃
• Properties of acids


  • Conduct electricity in aqueous solutions
  • Sour taste
  • Change the colour of indicators
  • React with water to form hydronium ions
  • Contain hydrogen atoms
  • Neutralise bases
  • React with many metals to produce hydrogen gas and a metal salt
  • React with carbonates to produce carbon dioxide, water, and a metal salt
• Hydronium ions


  H₃O⁺ ions formed when acids react with water
• Bronsted-Lowry acid


  A substance that donates a proton (H⁺)
• Bronsted-Lowry base


  A substance that accepts a proton (H⁺)
• Properties of bases

  • Taste bitter
  • Feel soapy
  • Change the colour of indicators
  • Conduct electricity in aqueous solution
  • Form hydroxide ions (OH⁻) in water
  • Neutralise acids
• Alkalis


  Bases that dissolve in water
• Strong acid

  Ionises completely in water
• Weak acid


  Ionises incompletely in water
• Strong and weak acids

  • A strong acid ionises completely in water and forms a high concentration of H₃O⁺ ions
  • A weak acid ionises incompletely in water and forms a low concentration of H₃O⁺ ions
• Strong and weak bases

  • A strong base dissociates completely in water and forms a high concentration of OH⁻ ions
  • A weak base dissociates/ionises incompletely in water and forms a low concentration of OH⁻ ions
• Bases (ionic compounds) dissociate in water to form ions
• Concentrated acid or base


  Contains a large amount of acid or base particles per volume of solution
• Dilute acid or base


  Contains a small amount of acid or base particles per volume of solution
• Acid-base reaction


  Involves the transfer of a proton (H⁺) and is called a protolytic reaction
• Conjugate acid-base pair

  Formed when an acid donates a proton and a base accepts a proton
• A weak acid always has a strong conjugate base
• A strong acid always has a weak conjugate base
• Ampholyte


  A substance that can act as either a base or an acid
• H3O is called the hydronium or oxonium ion
• Hydrochloric acid

  • HCl
  • Strong
• Nitric acid


  • HNO3
  • Strong
• Sulfuric acid


  • H₂SO4
  • Strong
• Phosphoric acid


  • H3PO4
  • Weak
• Carbonic acid/hydrogen carbonate


  • H₂CO3
  • Weak
• Ethanoic acid

  • CH3COOH
  • Weak
• Oxalic acid


  • (COOH)₂
  • Weak
• pH scale


  A scale of numbers from 0 to 14 used to express the acidity or alkalinity of a solution
• An acid is below 7 on the pH scale