pH
The pH scale is a mathematical
creation. It is a negative logarithm of the number of hydrogen ions (H+)
in a solution, expressed as a number between 1 and 14, without units.
- A logarithm is a way
of restating an exponent. It's not the measurement itself, but the number
of times you multiply to produce the actual number.
- Think of it like
a ratio: The number of hydrogen ions per X number of dissolved
molecules.
- The pH scale only
reflects unmatched or net H+ ions.
The pH Scale
| 1 |
7 |
14 |
| The lower the pH, the more acid the
substance. |
Pure
water has a neutral pH of 7 |
The
higher the pH, the more alkaline the substance |
| An acid is a substance that, when dissolved
in water, produces a net of hydrogen (H+)
ions. |
|
An
alkali is a substance that, when dissolved in water,
yields a net of hydroxide (OH-) ions. |
Instant
Feedback:
Low
pH is:
If you have
one H+ and one OH- together, you have water.
(H+) +
(OH-) = H2O
- What's the significance
of the OH- ion?
- From the above equation
you can see that OH- would neutralize H+ if it were available.
- You might think of
OH- as "negative hydrogen", or "anti-hydrogen."
- If you have one H+
and there is an OH- available, the H+ would be neutralized.
- You will not
increase the free H+ until you use up the OH-.
- There is such a thing
as pOH, (though
for practical purposes, we never use it.)
- H+ is
now "anti OH-" and neutral is still neutral.
- H+ and
OH- are such perfect opposites that they're "almost the
same."
Points to remember:
- The pH scale goes from
1 to 14.
- Low pH is acid.
- High pH is alkaline.
- pH 7 is Neutral
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