Acids & Bases

• pH scale


  Measure of how acidic or alkaline a solution is, ranging from 0 to 14 with low numbers being most acidic and high numbers being most alkaline
• Neutral substances like pure water have a pH of 7, which is neither acidic nor alkaline
• Acidic substances


  • Stomach acid (pH 2)
  • Acid rain (pH 4)
• Alkaline substances


  • Washing up liquid (pH 9)
  • Bleach (pH 12)
• Measuring pH


  1. Using indicator dyes that change colour

  2. Using a pH probe connected to a pH meter
• Indicator dyes


  A group of chemical dyes that change colour depending on the pH, with some containing a mixture of dyes that change across a wide pH range
• Universal indicator


  A common wide range indicator that changes colour from deep red (acidic) to bluish purple (alkaline)
• pH probe and meter


  • More accurate and precise than indicator dyes as it removes the need for human judgement of colour
• Acid


  Any substance that forms aqueous solutions with a pH less than 7, releasing hydrogen ions in water
• Base


  Any substance with a pH greater than 7
• Alkali


  A subgroup of bases that are soluble in water, forming hydroxide ions
• Neutralization reaction


  Reaction between an acid and a base, producing a salt and water
• Common acids


  • Hydrochloric acid - HCl
  • Sulfuric acid - H2SO4
  • Nitric acid - HNO3
• Common bases


  • Sodium hydroxide
  • Calcium carbonate