Strong and weak acids

• Acids


  Produce protons (H+) in water
• Acid ionisation


  1. Acid molecule dissociates

  2. Releases H+ ions
• Strong acids


  • Sulfuric, hydrochloric, nitric acids
• Strong acids


  • Ionise almost completely in water
  • Large proportion of acid molecules dissociate to release H+ ions
  • Tend to have low pH
• Weak acids


  • Ethanol, citric, carbonic acids
• Weak acids


  • Do not fully ionise in solution
  • Only a small proportion of acid molecules dissociate to release H+ ions
  • pH tends to be around 2-6
• Ionisation of weak acid

  1. Reversible reaction

  2. Equilibrium mixture formed
• Since only a few of the weak acid molecules release H+ ions, the equilibrium lies well to the left
• Acid strength


  Tells you what proportion of the acid molecules ionise in water
• Concentration


  Measures how much acid there is in a litre of water
• When an acid has a lot of acid molecules packed into a small amount of water, it is said to be concentrated
• An acid with a low proportion of acid molecules compared to the volume of water is said to be dilute
• Concentration describes the total number of dissolved acid molecules, not just the number of molecules that produce hydrogen ions
• The more grams (or moles) of acid per 1 dm³, the more concentrated the acid is
• You can have a dilute but strong acid, or a concentrated but weak acid
• As the concentration of H+ ions increases by a factor of 10

  The pH decreases by 1
• If the H+ ion concentration increases by a factor of 100

  The pH decreases by 2
• Decreasing the H+ ion concentration by a factor of 10

  Increases the pH by 1
• Acids are acidic because of H+ ions
• Strong acids are strong because they let go of all their H+ ions at the drop of a drop of water
• Strong acid - completely ionises
• Hydrochloric acid is a strong acid as it dissociates into H+ and Cl- ions.
• Aqueous solution - dissolved in water
• An indicator is used to determine whether something is acidic or alkaline.