Name:____________________
Lab Group Members:________________________________________Period:____
THERMAL POLLUTION
Background: An important relationship exists between the amount of dissolved oxygen in a pond and its temperature. Simply put, the warmer the water, the less dissolved oxygen and vice versa. For this reason, heat or “thermal” pollution is a very real problem especially in shallow ponds which get very warm in mid-summer. Most fish simply can’t stand warm water and/or low levels of dissolved oxygen.
Yeast represent the microorganisms, milk is the biodegradable waste. and methylene blue is used to indicate when oxygen is used up. The methylene blue changes from blue to white when no more oxygen is present in the test tubes. (The color change is actually from blue to colorless; the white color you’ll observe in the test tubes is due to the milk’s color).
Purpose: To determine how water temperatures affect the speed at which microorganisms use oxygen.
Materials : graduated cylinder, thermometer, (2 ) 250 ml beakers, methylene blue solution, 3 test tubes in rack, 10 ml graduated cylinder, eye dropper, heat source, milk, yeast, stirring rod, small beaker
Procedure:
1. Place 150 ml of water in two 250 ml beakers.
2. Heat the water in one beaker until it reaches a temperature of 37¡C. Remove the beaker from the heat source and set it aside.
3. Place the second beaker on the heat source and heat it to 100¡C (boiling).
4. Place 2mL of milk in each of the three test tubes. Add three drops of methylene blue to each test tube.
5. Place a cork over a test tube and mix the contents of the test tube with a stirring rod. Clean the stirring rod.
6. Prepare a sample of yeast solution by adding 2ml of yeast to 10ml of water in a small beaker. Mix the yeast and water with the stirring rod.
7. When the water in the second beaker has reached boiling, remove the beaker
from the heat source and set it aside.
8. Add 2ml of yeast solution to each of the three test tubes and mix the contents with the stirring rod.
9. Set one test tube into the beaker of near-boiling water, one test tube into the warm water and leave one test tube in the rack at room temperature.
10. Record the exact time your started the experiment (placed the tubes in water) in the table below.
| . | 1 |
2 |
3 |
| Temperature in Celsius | . | . | . |
| Time of Starting | . | . | . |
| Time Color Changed to White | . | . | . |
| Total Time for Color Change to Occur (Min) | . | . | . |
1. If a fish needs a lot of oxygen, would you expect to find it living in cold water or warm water?______________WHY?_________________________________
__________________________________________________________________________
2. What is the variable in this experiment?___________________________________
3. Chemical reactions speed up when temperatures increase. How would raising the temperature of a river affect the metabolism of fish and aquatic
organisms living there?___________________________________________________
__________________________________________________________________________
4. If a fish were taken from cold water and placed in warm water, would it breathe
faster or slower?_________WHY?___________________________________
__________________________________________________________________________
5. A number of different results were possible in this experiment. Your color changes may have proceeded in any order:
*make a hypothesis for the correct choice and circle it*
a) Hot tube changed first, warm tube second, room temp. last
b) Warm tube first, hot tube second, room temp. last
c) warm tube changed first, cold second, hot tube--no color change
6. What were your results?___________________________________________________
7. Explain your results.______________________________________________________
__________________________________________________________________________
8. Look at the chart to answer the following questions:
a) At 18º C, how much dissolved oxygen is present?___________________ppm
b) When dissolved oxygen is at 7ppm, what temperature is the water?______