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lewis concept of acids and bases
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 pair 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 an electron pair acceptor, a Lewis acid.
NH3 has a lone pair of electrons and is a Lewis
base.
the pH of a solution
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?
| pH =
-log[H+] = -log[2.9 x 10-4] =3.54 |
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The pH of this solution is less than 7 so this orange juice is
acidic.
hydroxide-ion concentration
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:
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.
| pOH = -log[1.9 x
10-3] = 2.72 |
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Now we want to find the pH by subtracting:
| pH = 14.00 - pOH =
14.00 - 2.72 = 11.28 |
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