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Chemistry
the pH scale
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pH scale
Used to measure the
strength
of
acids
and
bases
and to determine which solution is more
acidic
or more
basic
(
alkaline
)
Acids
Substances
with a
pH value less
than
7
Bases
/
Alkalis
Substances
with a
pH value greater
than
7
Lower
pH
More acidic
substance is
Higher
pH
Less acidic substance
is
Lower pH
Less basic
/
alkaline substance
is
Higher pH
More
basic
/
alkaline
substance is
PH
increases
Concentration of H<sup>+</sup> ions
decreases
PH
decreases
Concentration of H<sup>+</sup> ions
increases
PH increases
Concentration of
OH
<
sup
>
-
</sup> ions
increases
PH
decreases
Concentration of
OH
ions decreases
Neutral
solution
Concentration of
H
<
sup
>
+
</sup> ions is equal to
OH
<
sup
>
-
</sup> concentration
Water
molecule
Isn't
ionic
, but is able to
ionize
to a very small extent
Water ionization
H₂O
⇌ H+ +
OH-
Any
water
solution contains both
hydrogen
and hydroxide ions
Concentration
of H+ (hydrogen ion)
Inverse
relationship with
concentration
of OH- (hydroxide ion)
pH
Measure of the
acidity
or
basicity
of a solution
pH
7
is a
neutral
solution
Concentration of H+
Decreases
as pH
increases
Concentration of OH-
Increases
as pH
increases
In a
pure
/neutral solution, [H+] = [
OH-
]
Acidic
solution
[
H+
] > [
OH-
]
Basic solution
[OH-] > [H+]
pH +
pOH
=
14
(always)
Calculating pH from [H+]
pH =
-log
[
H+
]
pH
is a
logarithmic
scale
Each
pH
unit change represents a
10-fold
change in [H+]
The
water
molecule isn't
ionic
, but is able to ionize to a very small extent
Water ionization
H2O
+
H2O
⇌ H3O+ + OH-
Any
water
solution contains both
hydrogen
and hydroxide ions
pH scale
Measure of the
acidity
or
basicity
of a solution
Neutral
solution has a pH of
7
Acidic
solutions have a pH less than 7 (the lower the pH, the more
acidic
)
Basic solutions have a pH greater than
7
(the higher the pH, the more
basic
)
pH
log
[
H+
]
Finding pH from pOH
pH =
14
-
pOH
pH is a
logarithmic
scale, each unit change represents a factor of
10
change in H+ concentration