The pH scale: Chemical Changes: Chemistry: GCSE (9:1)

• Acid


  A substance that increases the hydrogen ion concentration of a solution.
• Base


  A substance that reacts with an acid and neutralises it
• Alkali


  A soluble base, that produces OH- ions in solution
• Types of chemicals that are bases

  Metal oxides, metal hydroxides, metal carbonates, ammonia
• Types of chemicals that are alkalis

  Metal hydroxides, ammonia
• Strong acids

  Acids that fully ionise in water
• Weak acids

  Acids that only slightly ionise in aqueous solution
• Ionise


  Split into ions
• pH


  A measure of H+ concentration
• Ions produced by acids

  H+
• Ions produced by alkalis

  OH-
• Neutral pH


  7

  
• pH of acids

  less than 7

  
• pH of alkalis

  more than 7

  
• Neutralisation reaction

  The reaction of an acid and a base forming a salt and water
• Ionic equation for an acid and an alkali

  H+(aq) + OH-(aq) --> H2O(l)
• Universal indicator


  An indicator with a different colour for each pH value.

  
• If pH decreases by 1

  hydrogen ion concentration increases x10
• At pH 7

  concentration of H+ = concentration of OH-
• Strong acid

  An acid that ionises completely in water

  
• Weak acid

  An acid that only partially ionises in water