The Lewis concept of acids is generalized to include reactions of acidic and basic oxides and many other reactions. A Lewis acid is something that can form a covalent bond by accepting an electron air from another species. A Lewis base is something that can form a covalent bond by donating an electron pair to something else. The Lewis and Bronsted-Lowery concepts are different ways of looking at the same chemical reactions. Here is a reaction in which an electron pair is transferred. The proton (H+) is electron pair acceptor, alewis acid. NH3 has a lone pair of electrons and is a Lewis Base.
Whether or not an aqueous solution is
neutral, acidic or basic depends on the hydrogen-ion concentration. We
give the acidity of an aqueous solution in terms of the pH. pH is defined
as the negative logarithm of the molar hydrogen-ion concentration. A pH of
7 means that a solution is neutral. A pH of below 7 means that a solution
is acidic; a pH of above 7 means that a solution is basic.
For example, let's say that we have a glass
of frosty orange juice. This orange juice has a hydrogen-ion concentration
of 2.9 x 10-4 M. What is the orange juice's pH?
The pH of this solution is less than 7 so
this orange juice is acidic.
We can also find pH by solving for the
hydroxide-ion concentration of a solution. The measure of the
hydroxide-ion concentration is called pOH.
Since we know that the pH scale goes from 0
to 14, we find that:
pH + pOH = 14
Let's say that we want to find the pH of an ammonia solution that has a hydroxide-ion concentration of 1.9 x 10-3 M. We start by finding the pOH.
Now we want to find the pH by subtracting:
pH = 14.00 - pOH = 14.00 - 2.72 = 11.28
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