Acids and Bases

• Universal indicator


  A mixture of indicators, allowing for testing a range of pH
• Universal indicator


  • It can detect the acidity or alkalinity of a solution
  • It estimates the concentration of hydrogen ions

  
• pH range of acid-alkali indicators

  • litmus: 5 - 8
  • methyl orange: 3.1 - 4.4
  • phenolphthalein: 8.3 - 10.0

  
• Acid-alkali indicators


  Change colour when an acid or an alkali is added
• Acid


  A substance that dissolves in water and forms hydrogen ions (H+)
• Acid reaction


  1. Acid + Salt

  2. H2

  3. H2O

  4. CO2

  5. Metal + Metal oxide

  6. Hydroxide or aq NH3

  7. CO3(2-) (carbonate)

  
• Acids


  • Many metals react with dilute acids to form a salt and hydrogen
  • Hydrochloric acid forms chlorides
  • Sulfuric acid forms sulfates
  • Nitric acid forms nitrates
• Acid reactions


  • Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)
  • CuO (s) + H2SO4 (aq) → CuSO4 (aq) + H2O (l)
  • NaOH (aq) + HNO3 (aq) → NaNO3 (aq) + H2O (l)
  • CuCO3 (s) + H2SO4 (aq) → CuSO4 (aq) + H2O (l) + CO2 (g)
  • NaHCO3 (s) + HCl (aq) → NaCl (aq) + H2O (l) + CO2 (g)
• Base


  A substance that can react with an acid
• Types of bases


  • Oxides
  • Hydroxides
  • Carbonates of metals
• Alkali


  A soluble base in water
• Alkalis


  • Turn damp red litmus paper blue
  • pH > 7
• Reaction of bases with acids

  1. Base + Acid → Salt + H2O

  2. Oxides + Acid → Salt + H2O

  3. Hydroxides + Acid → Salt + H2O

  4. Carbonates + Acid → Salt + H2O + CO2
• Reaction of alkalis with ammonium salts


  Alkali + Ammonium salt → Salt + NH3 + H2O

  
• Neutralisation reactions


  • CaO (s) + 2HCl (aq) → CaCl2 (aq) + H2O (l)
  • CuO (s) + H2SO4 (aq) → CuSO4 (aq) + H2O (l)
  • NaOH (aq) + HNO3 (aq) → NaNO3 (aq) + H2O (l)
  • CuCO3 (s) + H2SO4 (aq) → CuSO4 (aq) + H2O (l) + CO2 (g)
  • NaHCO3 (s) + HCl (aq) → NaCl (aq) + H2O (aq) + CO2 (g)
• Neutralisation


  Acid + Base → Salt + Water
• Acids in solution contain H+ ions, alkalis in solution contain OH- ions
• Acid


  Proton donor, gives a proton to a base
• Base


  Proton acceptor, removes a proton from an acid
• H+ (aq) + OH- (aq) → H2O(l)
• Reactions with ammonium salts

  • KOH (aq) + NH4Cl (aq) → KCl (aq) + NH3 (g) + H2O (l)
  • NaHCO3 (s) + NH4Cl (aq) → NaCl (aq) + NH3 (g) + H2O (aq) + CO2 (g)

  
• Strong acid


  Produces a lot of H+ ions, dissolves and dissociates easily, pH 1-3
• Weak acid


  Produces few H+ ions, dissolves but does not dissociate easily, pH 3-6
• Strength of acids and alkalis

  • Ease of dissociation
  • Concentration
  • Conductivity
  • Rate of reaction
• Strong alkali


  Produces a lot of OH- ions, dissolves and dissociates easily, pH 12-14
• Weak alkali


  Produces few OH- ions, dissolves but does not dissociate easily, pH 8-11
• Oxide


  Compound of a metal or non-metal with oxygen
• Types of oxides


  • Basic
  • Acidic
  • Neutral
  • Amphoteric
• Basic oxides


  • React with acids to form salts
  • Do not react with alkalis
  • Most do not react with water (except Group I and II)
• Acidic oxides


  • React with alkalis to form salts and water
  • React with water to form an acidic solution
• Neutral oxides


  Have a neutral pH
• Amphoteric oxides


  React with both acids and bases to form salts and water