Polyprotic Acids/Bases

Polyprotic acids/bases

A _____________ acid is an acid that has two or more ionizable hydrogen atoms per formula unit. Each ionization has its own ionization constant, where each subsequent ionization has a much _____________ ionization constant than does the prior ionization for two reasons: (1) The prior ionization produces hydronium ions that repress further ionization, in accordance with _____________ principle, and (2) the conjugate base that results from the loss of the first ionizable hydrogen is usually a _____________ ion, and it is more difficult to remove a positive H+ from a negative ion. The hydrogen ions in a solution of a polyprotic acid therefore come mainly from the _____________ step in the ionization. Determining concentrations at equilibrium can be difficult for polyprotic acids unless the Ka values are several orders of magnitude apart in strength. Under those conditions the ‘x is small’ approximation can be used with each ICE table to make it manageable.

 

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Practice Problems

 

  1. Oxalic acid, H2C2O4, is diprotic.

Write the two ionization reactions for oxalic acid.

 

Write the Ka1 and Ka2 expressions for oxalic acid