Types of Acids and Bases


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Arrhenius acids and bases

 

  • Acids are hydrogen containing compounds that ionize to form hydrogen ions in aq solutions
  • bases are compounds that ionize to produce hydroxide ions in aq solution.  

 

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Arrhenius Acids

  • Acids that contain only one ionizable hydrogen are called monoproticacids like HNO3,
  • Acids that contain two ionizable hydrogen atoms are called diprotic acids like H2SO4,
  • acids that contain three ionizable hydrogen atoms are triproticacids like H3PO4. 
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Types of Ionizable Hydrogen's

  • Only the hydrogens in very polar bonds are ionizable, which means that hydrogen is attached to a very electronegative element
  • Methane has four hydrogen CH4 but they are attached by a very weak polar bonds so none of the hydrogens are ionizable, so methane is not an acid even though it contains hydrogen.
  • In CH3COOH there is only one ionizable hydrogen (the one attached to the oxygen) so this is a monoprotic acid even though there are four hydrogens.
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Bronsted- Lowery acids and bases

  • An acid is a hydrogen ion donor and a base is a hydrogen ion acceptor
  • Ammonia is a base because when it is dissolved in water it accepts a hydrogen from the water to form ammonium ions and hydroxide ions.  
  •     NH3  +  H2O --> NH4+  + OH-
  • In this reaction ammonia is the hydrogen ion acceptor and is therefore the Bronsted – Lowery base, water is the acid because it donates the hydrogen.
  • This causes the hydroxide ion concentration to be larger than that of pure water, hence a basic solution.
 
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Conjugate Pairs

  • In the reverse reaction ammonium is the acid and hydroxide is the base.
  • This is known as a conjugate acid because it is the particle formed when a base gains a hydrogen ion and OH- is the conjugate base to water.
  • For every Bronsted – lowery acid base pair there is always a conjugate base – acid pair.
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Lewis acids and bases

  • An acid is a substance that can accept a pair of electrons and a base is a substance that donates a pair of electrons to form covalent bonds.
  • A hydrogen ion can accept a pair of electrons to form a bond and is therefore a Lewis acid.
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Summary

Type                       Acids                                 Bases

Arrhenius               H+ producer                     OH - Producer

Bronsted –Lowry    H+ Donor                          H+ Acceptor

Lewis                     Electron pair acceptor    Electron pair donor

 

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