Acids and Bases

Acids and Bases

1. Arrhenius' theory of acids and bases

   • Acid- A substance that dissociates in water to form H+ ions
   • Base-A substance that dissociates in water to form OH- ions
   • Limitations of the Arrhenius Definitions
     • 1. Acid-Base reactions are considered only in aqueous solutions.
     • 2. The OH- ion is singled out as a source of the basicity and therefore certain insoluble oxides cannot be classed as Arrhenius bases E.g. CuO
     • 3. The action of amphoteric species can't be explained

2. Strong and Weak Acids

   • H2SO4 and HCl are strong acids. A strong acid is one that dissociates (break up) fully in aqueous solution.
   • A weak acid is one that does not dissociate fully in aqueous solution. Examples include Ethanoic Acid and Methanoic acid (Formic acid).

3. Neutralisation

   • Neutralisation is the reaction between an acid and base to form salt and water.
   • Acid + Base = Salt + Water
     • HCl + NaOH = NaCl + H2O
   • A salt is a substance formed when the Hydrogen of an acid is replaced by a metal or an ammonium ion
   • Everyday Examples of Neutralisation
     • Wasp stings are basic They can be neutralised with vinegar or lemon juice
     • Nettle, bee and ant stings are acidic They can be neutralised with baking soda

4. Definitions

   • Conjugate acid
     • An acid changes into a conjugate base when it donates a proton.
   • Conjugate base
     • A base changes into a conjugate acid when it accepts a proton.
   • Conjugate pair
     • A conjugate acid-base pair is any pair consisting of an acid and a base which differs by one proton
   • Bronsted Acid
     • An acid is a proton donor
   • Bronsted Base
     • A base is a proton acceptor.
   • Amphoteric
     • A substance that can act as an acid or a base is said to be amphoteric.