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Graded Assignment
SCI113B: Earth Science | Unit 3 | Lessons 5 and 6: Laboratory: Dissolved Oxygen
Name:
Date:
Graded Assignment
Lab Report: Dissolved Oxygen Lab
Answer the questions below. When you are finished, submit this assignment to your teacher by the due date for
full credit.
You will need to use the Student Guide for directions, as well as the Virtual Lab. Additionally, you may choose to
watch the following recording in order to get more detailed help with each question.
Record the number of drops of Reagent D needed to turn the solution light blue in each phase of the lab:
Set-Up Observations
Phase
Amount of water
mL or drops
Amount of yeast
mL or drops
(20 drops = 1mL)
1
6 mL
none
2
6 mL
10 drops
3
6 mL
20 drops or 1mL
(12 points)
1. Complete the data table.
Score
Answer:
Experiment Observations
Phase 1
Phase 2
Phase 3
O2 concentration in
ppm (parts per
million) = number of
drops of Reagent D
added to reach blue
color (oxygen
completely depleted)
and observations
(3 points)
2. Regarding Phases 2 or 3 of the experiment, if more or fewer drops of Reagent D (sodium
hydroxide) were needed to get the same blue color as in Phase 1, what does this tell us about
the quality of the water when yeast was consuming nutrients in the water? Did something
similar to eutrophication occur?
Score
Answer:
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Copying or distributing without K12’s written consent is prohibited.
Page 1 of 3
Graded Assignment
SCI113B: Earth Science | Unit 3 | Lessons 5 and 6: Laboratory: Dissolved Oxygen
(3 points)
3. What would happen to the dissolved oxygen in the Missouri River if large amounts of waste
were dumped into it?
Score
Answer:
(3 points)
4. Under favorable conditions, bacteria can multiply every 20 minutes. Starting with one bacteria
cell, how many bacteria should you expect after 15 hours? Hint: Under favorable conditions,
if one bacterium becomes 2 in 20 minutes (1 multiplied by 2), those 2 become 4 in the next
20 minutes, and then those 4 become 8 in the next 20 minutes. That means that 8 bacteria
resulted in 1 hour. Now calculate the growth of bacteria for 15 hours.
Score
Answer:
(3 points)
5. In this lab, you continued to add Reagent D to each solution until it turned blue. The purpose
was to remove the oxygen to measure how much was left. The more drops you had to add to
acquire the blue color, the more oxygen was present in the tube. In which phase(s) did the
solution turn blue before you added Reagent D? What do you think that means?
Score
Answer:
© 2007 K12 Inc. All rights reserved.
Copying or distributing without K12’s written consent is prohibited.
Page 2 of 3
Graded Assignment
SCI113B: Earth Science | Unit 3 | Lessons 5 and 6: Laboratory: Dissolved Oxygen
Further Uses
(3 points)
6. Now that you’ve seen how decomposition affects the amount of dissolved oxygen, collect
three samples from somewhere in your house or community. You can get water from a
puddle, a drinking fountain, a stagnant bowl of pet water, a stream, a pond, or fresh
rainwater—be creative. Then, see how much dissolved oxygen you find in the sample.
Score
Yes, you DO need answer this question! Don't worry about actually finding the samples and testing them. You
can just use the information taken from Ms. Kanine’s recording. She picked three kinds of water (puddle water,
rain water, and dog bowl water), and predicted the amount of dissolved oxygen in them.
Check out Ms. Kanine’s answers at the link above. If you choose to use this information, be sure that
you put the observations and conclusions in your own words.
Answer:
Sample
Location
Signs of
Decomposition
(List any visible
microorganisms that
might indicate
decomposition.)
Prediction for
Dissolved
Oxygen Level
Results for
Dissolved
Oxygen
Your Conclusion
(Would this
location support
aquatic life?)
1
2
3
Your Score
© 2007 K12 Inc. All rights reserved.
Copying or distributing without K12’s written consent is prohibited.
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