Carbon Dioxide, Acid Rain, and Acid Buffering Capacity
Objective
This lab will demonstrate how carbon dioxide, when dissolved in water, forms
carbonic acid, a weak acid. It will be shown how the alkalinity of different rocks can be
recognized and how this relates to the acid buffering capacity of natural bodies of water.
Procedure
Part I
1. Take one can of cold carbonated beverage and one can of warm carbonated
beverage and shake them gently.
2. Open each of the cans while holding them over the sink. Record what occurs in
the table below.
3. With a nail and hammer, make a small hole in the top of a warm can of
carbonated beverage. The hole should be about the same diameter as the straw.
4. Carefully slip the straw into the can. Hold the other end of the straw in the beaker
filled with limewater. CAUTION: Limewater may irritate the skin. Avoid
contact. Record your observations in the table below.
Part II
1.
2.
3.
4.
5.
6.
Take a piece of granite and a piece of limestone and place each on a piece of
paper towel.
Place two drops of vinegar on the granite and record your results in the table
below.
Place two drops of vinegar on the limestone and record your results in the table
below.
Take some granitic sand and a crushed up antacid tablet and place on separate
pieces of paper towel.
Place two drops of vinegar on the granitic sand and record your results in the
table below.
Place two drops of vinegar on the crushed up antacid tablet and record your
results in the table below.
Data and Observations
Part I
Can
Observations
Part II
Rock
Observations
Cold
Warm
Limewater
Granite
Limestone
Granitic Soil
Crushed Up Antacid Tablet
Questions and Conclusions
1. What gas is present in a carbonated drink?
2. What happens when you opened the two cans and why?
3. Which can lost its carbon dioxide faster and why?
4. Describe what happens when the beverage and the limewater are combined.
5. As the carbonic acid descends underground to greater depths, it dissolves CaCO3
(calcium carbonate). If the temperature were to increase, what would happen to
the CaCO3?
6. As the carbonic acid seeps through the roof of a cave, part of the water
evaporates. What happens to the calcium carbonate?
7. If underground water circulates close to the vent of a volcano, it might dissolve
carbon dioxide. Would increased pressure or high temperature cause the carbon
dioxide to dissolve?
8. Did you observe a difference in the reactions between the acid dropped on granite
and on limestone? Why?
9. Which rock acted as a buffer?
10. When the increased surface area was exposed to acid, did the previously observed
reactions change?
11. Why does limestone fizz when it is exposed to acid? What are the bubbles?