Download OceanpH - Chemistryland

• The bad news, good news and more bad news
about elevated CO2 levels in the atmosphere.
– Bad news: CO2 contributes to global warming.
– Good news: The ocean is absorbing a good deal of
this CO2, therefore slowing global warming.
– Bad news: As the excess CO2 dissolves in the
ocean, the ocean becomes more acidic, therefore
threatening marine life that uses calcium carbonate to
build its skeleton or shell. Think of coral, lobsters,
star fish, and mollusks.
• In experiment #2, we showed that CO2
comes from car exhaust as the engine
burns gasoline making CO2 and water.
• When CO2 dissolves in water, we showed
that it becomes carbonic acid. If this water
is the ocean, this acid threatens the
marine animals that use calcium
carbonate to create their exoskeletons and
shells.
• There are many ways humans have damaged marine life; for example,
pollution, over fishing, dredging, and blasting are the obvious ways.
Adding carbon dioxide to the atmosphere is a more hidden way of harming
marine life; a way that slowly dissolves their bodies.
• Many sea creatures build the shell or exoskeleton using calcium
carbonate. This is how it can be dissolved:
• First the carbon dioxide combines with water to make an acid called
carbonic acid.
• CO2 + H2O  H2CO3
• Like most acids, the carbon acid releases a hydrogen ion (H+). It’s called
an ion because it has a charge. In this case, it’s a plus one charge. The
hydrogen ion (H+) is the calling card of acids.
• H2CO3  HCO3- + H+
• The hydrogen ion attacks the solid calcium carbonate in the shell (or
exoskeleton) causing the calcium to dissolve into the water. The CO32(called the carbonate ion) combines with H+ to make what’s called the
bicarbonate ion (new name is hydrogen carbonate, which also dissolves in
the water (ocean). The outcome is the marine animal looses it’s shell or
exoskeleton and dies.
• HCO3-  H+ + CO32• CaCO3 + 2H+ + CO32-  Ca2+(aq) + 2HCO3• CaCO3 + CO2 + H2O → Ca(HCO3)2
• CaCO3(s) + H+(aq) Ca2+(aq) + HCO3-(aq)
O
H
+
H
H
O-
O
O
C
Ca2+
Ca2+
O-
OO-
O
O
OCa2+
O
O-
O
Ca2+
O-
H
OCa2+
O
C
+
O
O-
C
O-
O-
C
Ca2+
H
C
O-
O-
O
H
C
C
Ca2+
O-
+
C
Ca2+
O-
O-
O
O-
O-
O-
C
Ca2+
O
O
C
Ca2+
O-
6
H
+
H
O
H
1
H+
ions
O-
+
O
O
O
C
Ca2+
O-
O-
Ca2+
2
O-
Ca2+
O
+
O
O-
+
O
O
C
Ca2+
O-
O-
O-
+
+
O
Ca2+
O
C
O-
O-
O
C
O-
O-
O
+ C
5 O
C
Ca2+
H
O
C
3
Ca2+
O-
O-
C
Ca2+
O-
OCa2+
+
C
C
O-
O-
O
+
O-
O-
O-
O
OCa2+
O-
O-
+
H
C
C
Ca2+
+
Ca2+
O-
O-
O
O
H
C
C
Ca2+
4
+
Ca2+
O-
O-
O
C
Ca2+
O-
H+
H+
H
H
O
Ca2+
O-
O- C
O
O-
O
C
O-
O-
Ca2+
C
O-
O
O-
O
O
O-
C
C
Ca2+
H+
Ca2+
OCa2+
H+
O-
OO-
O
C
Ca2+
O-
O
C
Ca2+
O-
• To demonstrate that CO2 makes water acidic,
we will bubble CO2 through water. Instead of
the source of CO2 being your automobile, it will
be yourself. Yes, you contribute to global
warming and to the oceans acidity, too (but to a
much lesser amount).
• We will detect the CO2 in two ways. Both ways
show that the acidity of water increases when
CO2 is added. One way of showing it is by
directly measuring pH. The other is similar to
what we did in the car exhaust lab, but this time,
you will provide the CO2.
• The amount of CO2 that dissolves in water depends on the
temperature of water. You know this from experience. If you open a
soda can while warm, it’s likely to spray all over as the CO2
hurriedly leaves the water to become a gas. If cold, more CO2 stays
dissolved in the water as either CO2 or as H2CO3.
• We are going to blow into a beaker of ice water using some tubing
attached to an air stone. The concentration of CO2 in air from our
lungs is about 4% (that’s about 4 CO2 molecules (with the remaining
100) being water, oxygen, and nitrogen molecules), 5 water (H2O)
molecules, 15 oxygen (O2) molecules, and 76 nitrogen molecules
(N2). With the car exhaust, CO2 concentration was about 12% (12
CO2, 75 nitrogen molecules, and 13 H2O.
• CH3(CH2)6CH3 + 12.5 O2  8CO2 +
9H2O
• 12.5 to x = 20 to 80 ( 4 x 12.5)=50
• 50 molecules N2 : 8CO2 + 9H2O