Strong Acids and Bases

Learning Goals

You will learn a little about the method of ranking of acids and bases.

Synopsis

Looking at the listing of strong acids we see that HClO4 is ranked above HCl and that HCl is ranked above H3O+. We have previously stated that the stronger acid is the one that more completely donates a proton. But in water solution both HClO4 and HCl are completely dissociated. Water is a strong enough base to accept protons from either acid and so water has a leveling effect on the strength of these very strong acids. In a water solution we cannot differentiate between the strengths of these two acids. So how do we differentiate between these acids? We need to use a solvent that is a weaker base than water so that it will more readily accept protons from the stronger acid than from the weaker acid. Such a solvent is called a differentiating solvent. Diethyl ether, C2H5OC2H5, is a weaker base than water, and in diethyl ether HCl is only partially dissociated, but HClO4 is still totally dissociated. So we can then state that HClO4 is a stronger acid than HCl. However, we will be mainly concerned with acid-base activity in aqueous solutions and in such solutions all acids at and above H3O+ are equally strong. We can make the same statement regarding bases at and above OH- in a water solution.

On-Line Activity

Do a web search for differentiating solvents and see what more you can learn about this method of differentiating between acids of equal strength in a water solution.


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Web Author: Dr. Leon L. Combs
Copyright 2000 by Dr. Leon L. Combs - ALL RIGHTS RESERVED