Ocean Acidification Process
GCSE Science
Why study ocean acidification?
– The oceans contain 50 times more carbon dioxide
than the atmosphere
– The ocean pH has decreased by 0.1 of a unit,
representing a 29% increase in hydrogen ions since
the Industrial Revolution
– The oceans absorb roughly 30% of humangenerated carbon dioxide
GCSE Science
– pH is the unit used to
measure acidity
– The lower the pH value, the
greater the acidity
Increasing acidity
Why is pH?
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Drain cleaner
Ammonia
Soap
Baking soda
Water
Milk
Banana
Tomato
Vinegar
Lemon
Hydrochloric acid
GCSE Science
Atmospheric
CO2
Ocean acidification process
CO2 dissolves in
water
CO2 (aq)
Carbon dioxide in the atmosphere dissolves in the oceans.
Atmospheric
CO2
CO2 dissolves in
water
CO2 (aq)
Ocean acidification process
Forms Carbonic
Acid
H 2CO3
This aqueous carbon dioxide reacts with the water to form carbonic acid.
Atmospheric
CO2
CO2 dissolves in
water
CO2 (aq)
Ocean acidification process
Forms Carbonic
Acid
Breaks down to form
bicarbonate and
hydrogen ions
H 2CO3
H+
HCO3-
The carbonic acid breaks down to form bicarbonate and hydrogen ions.
The increase in hydrogen ions makes the oceans more acidic. So the more carbon
dioxide that is absorbed by the oceans, the more acidic they become.
Atmospheric
CO2
CO2 dissolves in
water
CO2 (aq)
Ocean acidification process
Forms Carbonic
Acid
Breaks down to form
bicarbonate and
hydrogen ions
H 2CO3
Carbonate ions react with
these ‘extra’ hydrogen
ions
H+
+
HCO3-
CO32-
Carbonate ions ‘buffer’ this increased number of hydrogen ions by forming more
bicarbonate ions.
Carbonate ions enter the oceans through processes such as the weathering of
limestone (CaCO3). This buffering decreases the amount of carbonate and
hydrogen ions in the oceans.
Atmospheric
CO2
CO2 dissolves in
water
CO2 (aq)
Ocean acidification process
Forms Carbonic
Acid
Breaks down to form
bicarbonate and
hydrogen ions
H 2CO3
Carbonate ions react with
these ‘extra’ hydrogen
ions
H+
+
HCO3-
CO32-
Organisms that form their shells or skeletons from carbonate will be affected
because there are fewer carbonate ions in the oceans.
The levels of ocean acidification may also reach a ‘corrosive’ level where these
shells or skeletons start to dissolve to ‘buffer’ the ocean pH.