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1. pH and Buffers

2. Water Characteristics
 The covalent bonds within the water molecule,
like the hydrogen bonds between the molecules,
can also break spontaneously. This is known as
water dissociation.
H2O  H+ + OH-
Water Hydrogen Ion Hydroxide Ion
 This doesn’t happen often, but enough. If you
have a beaker of pure water, 1/10,000,000
molecules are hydrogen ions.

3. pH
If you want to
mathematically
express the
concentration of
the hydrogen ions
found in a solution,
you would refer to
the solution’s “pH”.

4. Key Features of pH Scale
 Acid, Base, Neutral Range
Acids are molecules that donate hydrogen ions
to a solution.
In a chemical formula, acids start with “H”.
Ex. HCl, HF (hydrochloric acid, hydrofluoric
acid)
Bases are molecules that combine with
hydrogen ions to remove them from a solution
In a chemical formula, end with “OH”. Ex.
NaOH, KOH (sodium hydroxide, potassium
hydroxide)
 Scale is Logarithmic

5. Calculating pH: A
couple key formulas:
 [H+] + [OH-] = 1 x 10-14
 pH + pOH = 14
If given the concentration, pH or pOH is
simply the exponent on the 10.
Ex. [H+] = 1 x 10-2 the pH would be 2.
If given the pH, the [H+] would be calculated
by making the pH value the negative
exponent of the 10.
Ex pH = 9, [H+] = 1 x 10-9.

6. Why is pH important to
living organisms?
Key molecules, known as enzymes,
function at set pH values.
All our cells function within a certain pH
range.
If the fluids bathing those cells is “off”
these cells won’t function at max capacity.
Other than just cells, our blood needs to be
at a certain pH.

7. But…
The chemical reactions of life
constantly produce acids and
bases within cells. These have
a tendency to throw off the pH
values. We need some sort of
mechanism to minimize how
much the pH is altered.

8. Solution
Buffers: substance that can take up
or release hydrogen ions into a solution
so that the pH can maintain
equilibrium.
So...if pH is low, what about the
[H+]?
It is HIGH
 ...if pH is high, what about the
[H+]?
It is LOW

9. Buffers
 What would a buffer do if pH falls?
Remove hydrogen ions from the
solution.
 What would a buffer do if pH rises?
 Donate hydrogen ions to the solution.
 In living organisms a key buffer is known
as the Bicarbonate Ion Buffer System.