C3.3

• Oxidation


  Gain of oxygen
• Reduction


  Loss of oxygen
• Oxidation


  Loss of electrons
• Reduction


  Gain of electrons
• OIL RIG stands for Oxidation Is Loss and Reduction Is Gain (of electrons)
• Acids


  Form hydrogen ions when they dissolve in water
• Alkalis


  Contain hydroxide ions
• Neutralisation


  Acid reacting with alkali or a base to form a salt plus water
• The ionic equation for any reaction of an acid with an alkali (soluble base) is H+ + OH- → H2O
• Acid + metal carbonate


  Salt + water + carbon dioxide
• Acid + metal


  Salt + hydrogen gas
• Strong acid


  Completely ionised in aqueous solution
• Weak acid


  Partially ionised in aqueous solution
• Stronger an acid


  Lower the pH (for a given concentration of aqueous solutions)
• As the pH decreases by one unit, the H+ concentration of the solution increases by a factor of 10
• Strong and weak is NOT the same as concentrated and dilute - the latter refers to the amount of substance in a given volume whereas, the former refers to the H+ ion concentration in aqueous solutions
• pH scale


  Measures the acidity or alkalinity of a solution, can be measured using universal indicator or a pH probe

  
• pH 7


  Neutral
• pH < 7


  Acidic
• pH > 7


  Alkaline
• Stronger the acid


  Closer the pH value is to 0
• Stronger the alkali


  Closer the pH value is to 14
• Larger concentration of H+ ions

  More acidic pH value
• As hydrogen ion concentration increases by a factor of ten, the pH value of a solution decreases by a factor of one
• pH meter


  • Gives an exact pH value
• Universal indicator


  • Changes colour which can be compared to the pH scale
• Indicators


  • Methyl orange
  • Phenolphthalein
  • Litmus