Investigation 3
How much acid can the ocean absorb?
Introduction
Points
|130
Do you know what a coral is? Corals are actually little soft bodied animals, that build hard calcium-based shells
to protect themselves. The build up of the shells eventually forms what you know as a coral reef. However,
calcium is known to react strongly to acid. What do you think would happen if the pH (the relative measure of
acidity) changed enough in the ocean? How does acid rain affect the pH? Today you will perform a smallscale experiment to determine this.
Objectives
1. To determine how acid rain affects seawater chemistry.
2. To determine ocean acidification affects marine organisms.
3. To determine how environmental factors affect an ecosystem
4. To introduce appropriate laboratory procedure.
Materials
Florence flasks
Plastic pipettes
Synthetic Acid Rain
0.5x acid stock
Seawater
Assorted glassware
BTB pH indicator
Before Class
Go online and review the following video prepared by your teacher:
“Ocean Acidification”
Answer the following questions:
1. What is the compound that is of most concern in the ocean? (5pt)
2. What is the primary element in aragonite? (5pt)
3. What is pH? (5pt)
4. At what pH does aragonite dissolve? (5pt)
Procedure
1. Acquire your materials. You will need to pour 100mL of seawater into your Florence flask. Add enough of
the BTB indicator to change the solution to the color in the provided picture.
2. Knowing that BTB is an indicator, and is blue above a pH of 7.6 and yellow below a pH of 6, what could
you say about seawater in it’s natural state? (10pt)
3. You will be performing a basic titration of seawater to determine acidity. Begin with the 0.5x acid solution.
Add in acid in small increments (while keeping track of the volume of acid added) using the plastic pipette.
The pipettes are graduated up to 1mL, and remember that 20 drops make up 1mL. The end point of your
experiment will be when you reach the strong yellow color. You may want to match the color to the picture
provided.
4. Next, perform the titration using the Synthetic Acid Rain. Your end point will be the same yellow color.
Use the table below to keep track of your end point: (40pt)
Solution
Volume of Acid
5. What is the importance of the end point of the experiment? Why was BTB specifically chosen? (10pt)
Study Questions
1. Define Ocean Acidification. (10pt)
2. Besides physical atmospheric deposition of acid (acid rain) how else can the oceans become acidified? (10pt)
3. At a pH of 6, what starts happening in the ocean? (10pt)
4. Imagine that all corals worldwide are destroyed. Describe what would happen to the ecosystems after that
point? (10pt)
5. What would happen (hypothetically) if the oceans were suddenly alkanized with addition of something like a
strong Sodium Hydroxide solution? (10pt)