Student Lab: Serial Dilution and Chemical Toxicity

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Serial Dilution and Chemical Toxicity Lab
Objective:
To allow students to demonstrate an understanding of a serial dilution while assessing
the relative toxicity of a chemical.
Time:
This lab will take between 1 hour and 1½ hours.
Materials:
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6 large test tubes
Test tube rack
60 live brine shrimp per lab group
Liquid “toxic” substance to be tested
Salt water (1 teaspoon salt to 100 mls water)
10-ml graduated cylinder
Procedure:
1. Chose a “toxic” substance you would like to test. Your goal is to determine what
percentage of the substance will kill 50% of the brine shrimp. Label the test tubes 1
through 6.
2. Add 10 mls of the substance you are testing to test tube #1.
3. The next step is to set up a serial dilution. Add 9 mls of salt to each of the other 5
test tubes.
4. Remove 1 ml of the substance from test tube #1 and add it to test tube #2. Cover the
opening of the test tube and invert it 3 times.
5. Remove 1 ml of the substance from test tube #2 and add it to test tube #3. Cover the
opening of the test tube and invert it 3 times.
6. Remove 1 ml of the substance from test tube #3 and add it to test tube #4. Cover the
opening of the test tube and invert it 3 times.
7. Continue until you have done the serial dilution for 5 of the 6 test tubes. Do not add
liquid from test tube #5 to test tube #6. Instead, remove 1 ml of the substance from
test tube #5 and dispose of it. Test tube #6 is your control.
8. Now add 10 brine shrimp to each of the 6 test tubes.
9. After 10 minutes, count the number of live shrimp in each tube and record it in the
data table that follows.
10. Graph your results.
Data Table:
Concentration of toxic
substance
Number of shrimp still
alive
100%
10%
1%
0.1%
0.01%
Control (0%)
Graph:
Analysis:
1.
What does the term LD50 mean? Explain.
2.
What was the LD50 of your substance?
3.
Can the information you obtained be applied to humans? Why or why not?
4.
Do you have any concerns during this lab about doing testing on animals? Why or
why not?
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