In this module, you will create a model “lake." You will not be adding any substrate; we will investigate the effects of substrate on alkalinity in the next module. You will then use pH indicator paper to estimate the changes in pH as you add a common acid to simulate acid rain.

MATERIALS

• Goggles
• 250-mL Beaker
• 100 ml graduated cylinder
• Tap Water
• 10-mL Graduated Pipette
• Blue pipette pump
• pH Paper
• pH Color Chart
• “Acid Rain” in a 50-mL tube

PROCEDURE

Creating a data Table in Excel.

1. Open a new workbook in Excel.
2. Label the first column "Total Volume of Acid Rain Added (mL).
3. Enter the following volumes into cells in that column: 0, 0.1, 0.4, 1.6

Prepare a model “lake” with no substrate:

1. With your goggles on, using the 100 ml graduated cylinder, measure 15 mL of tap water and place in your 250 mL beaker.
2. Cut a 4-cm piece of pH paper off of the pH paper roll and hold it with one end in the water for 3 seconds then remove. Wait 15 seconds and then read the number on the pH roll that corresponds to the color of your pH paper. If you feel the color is in between 2 numbers you can use a 0.5 interval. For example, if you feel the color of your paper is not as orange as a 6 but not as green as a 7, you can call it 6.5. Don't make any other fractions of the numbers other than 0.5. Use this step 2 pH procedure for all pH readings.
3. Label the second column of your Excel table "No Substrate (pH)".
4. Record the pH reading for 0 mL of acid added in your table.
5. Measure out 0.5 mL of 'acid rain' with the graduated pipette and blue pipette pump and add it to the water in the beaker. It might be easier to use the pipette if you place the 50-mL tube of 'acid rain' in a cup or glass to hold it upright.
6. Swirl the beaker for 30 seconds.
7. Read the pH of this solution and record it on your table.
8. Repeat steps 5-7, three more times, adding 0.5 mL of acid each time, using a fresh piece of pH paper, and recording the new pH values of the water solution in your table.
9. Rinse your beaker out in your sink and dry it to use in the next experiment. The acid provided is relatively weak, and in low volumes, and will not damage plumbing or septic systems, nor is it harmful to the environment

MODULE 2: Investigate the effects of different substrates on the alkalinity of a lake

The alkalinity or buffering capacity of a lake is dependent on run-off into the lake, biological activity in the lake, and the composition of the lake bed. Most commonly, lake beds are composed of sediments originating from the erosion of regions neighboring the lake, organic debris, and precipitation of chemicals suspended in the waters of the lake. Rivers and streams draining into the lake deposit sediments while currents and wave action cause erosion that adds to the sediments. These sediments can consist of silt, sand, gravel, or clay. If the sediments are dark brown to black in color, there is usually a large concentration of organic material mixed in. Conversely, if the sediments are distinctly white, this often indicates a high amount of calcium carbonate. In this portion of the laboratory you will examine which types of sediments have a greater impact on buffering capacity.

MATERIALS

• Goggles
• 250-mL Beaker
• 100 ml graduated cylinder
• Tap Water
• 10-mL Graduated Pipette
• Blue pipette pump
• pH Paper
• pH Color Chart
• “Acid Rain” in a 50-mL tube
• digital balance

Containers with each of the following substrates:

• Sand
• Pebble stones/gravel (aquarium)
• Fluval Stratum (aquatic volcanic soil)
• Limestone (crushed coral)

Creating a Hypothesis:

One example of the basic research question for this module is: which types of lake sediments have the greatest impact on the buffering capacity of the lake? There are a few constraints in attempting to answer this question. For example, we are limited in our types of substrates and in our volumes of acid. However, a 'lake microcosm' (microcosm: a small model of a much larger real system) allows us to focus only on a limited number of variables while keeping many factors equal, or very nearly so. We can vary the substrate among 'lakes' while keeping the volume of the 'lake' and the influx of 'acid rain' the same for each different substrate treatment. This would not be possible by using real lakes for a number of reasons. Of course, it would be unethical to intentionally acidify natural lakes to dangerous levels, but it is also impossible to find any two lakes that have the exact same volumes, starting water chemistry, etc., with the only variation between them being the substrate. Microcosms are often used to create simplified versions of real systems so we can learn about particular variables of interest.

For this experiment, you will use a similar procedure as in Module 1: a container containing 15 mL of tap water to which you add 'acid rain' while measuring changes in pH. The main difference will be that there will also be 20 g of sediment forming a 'lake bottom.' You have a variety of sediments available to create your model lakes: sand, pebble stones (gravel), limestone (crushed coral), and Fluval stratum (organic soil). Your goal is to determine which sediments contribute best to the buffering capacity of the water.

Question 1

Consider the list of sediments above. Create a hypothesis based on the research question: “Which type of lake sediment has the greatest impact on the buffering capacity of the lake?” Remember, a good hypothesis is based on previous knowledge and is not just a guess. Look back at the information provided in the overall introduction and in the introduction to this module. You may also need to do some additional research regarding the nature of each of the substrate materials.

QUESTIONS

Based on your hypothesis, what is/are the independent variable(s) in your experiment?

(Select all that apply)

Group of answer choices

The starting pH of the water

A) The type of sediment

B) The size of the beaker representing the 'lake'

C) The temperature of the water

D) The volumes of acid added

E) The volume of the 'lake'

F) The mass of sediment

G) How long the 'lake' is stirred

Based on your hypothesis, what is/are the independent variable(s) in your experiment?

(Select all that apply)

1. Group of answer choices
2. The starting pH of the water
3. The type of sediment
4. The size of the beaker representing the 'lake'
5. The temperature of the water
6. The volumes of acid added
7. The volume of the 'lake'
8. The mass of sediment
9. How long the 'lake' is stirred

What will be the dependent variable(s) in your experiment?

(Select all that apply)

A) The pH change of the 'lake'

B) The type of sediment

C) How long the 'lake' is stirred

D) The volume of the 'lake'

E) The size of the beaker representing the 'lake'

F) The mass of sediment

G) The temperature of the water

H) The volumes of acid added

Identify the control variable(s) below:

(Select all that apply)

A) How long the 'lake' is stirred

B) The temperature of the water

C) The pH change of the 'lake'

D) The mass of sediment

E) The type of sediment

F) The size of the beaker representing the 'lake'

Did your results support or refute your hypothesis? Explain referring to your hypothesis and your data.