Acids & Alkalis

Acids & Alkalis

1. The pH Scale

   • Used to measure how acidic or alkaline a solution is
   • The strongest acid has a pH of 0
   • The strongest alkali has a pH of 14
   • A neutral substance (eg. water) has a pH of 7

2. Indicator Dye

   • The dye in an indicator solution changes colour depending on whether it's above or below a certain pH.
   • Universal Indicator is a combination of dyes that produce the colours in the diagram to the right depending on the pH of a solution
     • It's very useful for estimating the pH of a solution

3. Acids & Bases

   • Acids & Bases neutralise each other
   • An ACID is a substance with a pH of LESS than 7
     • Acids for H+ ions in water
   • A BASE is a substance with a pH GREATER than 7
     • An ALKALI is a base that DISSOLVES in water
       • Alkalis form OH- ions in water
   • H+ ions make solutions acidic
     • OH- ions make solutions alkaline

4. The reaction between acids and bases is called neutralisation

   • acid + base -> salt + water
   • H+ + OH- -> H2O
     • H2O (Water) has a neutral pH so this shows that an acid and bases neutralise each other

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