The pH scale

• Acidic solution


  Has a greater (more) concentration of H+ ions and has a pH of 1-6.9
• Neutral solution


  Has an equal concentration of H+ and OH- ions and has a pH of 7
• Alkaline solution


  Has a greater (more) concentration of OH- ions and has a pH of 8-14
• The pH scale is an indication of the hydrogen ion concentration and runs from below 0 to above 14
• Dilution of an acidic solution with water

  Decreases the concentration of hydrogen ions and the pH will increase towards 7
• Dilution of an alkaline solution with water

  Decreases the concentration of hydroxide ions towards 7
• Soluble non-metal oxides


  Dissolve in water forming acidic solutions
• Soluble metal oxides


  Dissolve in water forming alkaline (metal hydroxide) solutions
• Insoluble non-metal oxides added to water have no effect on the pH
• Insoluble metal oxides added to water have no effect on the pH
• Dissociation of water


  1. H2O breaks into H+ and OH-

  2. H+ and OH- can immediately recombine

  3. The reaction is reversible
• The number of H+ ions is always the same as the number of OH- ions in pure water, giving a pH of 7