Dissolved Oxygen, questions help

Lab Report

Answer the questions below. When you are finished, submit this assignment to your teacher by the due date for full credit.

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

1

6 mL

0.25mL

2

6 mL

0.25mL

3

6 mL

0.25mL


1. 
Complete the data table.

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


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?

Answer:


3. 
What would happen to the dissolved oxygen in the Missouri River if large amounts of waste were dumped into it?

Answer:


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.

Answer:


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?

Answer:

Further Uses

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.

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


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