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Serial Dilutions Getting ready for 25.1

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Serial Dilutions… Are a series of solutions in which each solution has a concentration that is an exact fraction, such as 1/2 or 1/10, of the previous solution.

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Serial Dilutions cont. Do you remember? 100% = 1.0

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Serial Dilutions cont. Do you remember? How to convert a percent to a number? e.g. 0.5% = 0.005

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Serial Dilutions cont. Since the units of a serial dilution are expressed in ppm (parts per million), we must multiply the numerical conversion we got previously by 1,000,000 So… X = 5000 ppm

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**So… 0.005 X 1000000 = 5000 ppm What does this mean? **

Serial Dilutions cont. So… X = 5000 ppm What does this mean?

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Serial Dilutions cont. So… X = 5000 ppm This means that if we have 1 million particles (ppm), 5000 of the particles are a specific substance and the remaining 995,000 are some other particle(s)

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**Video Example of Serial Dilution**

Video Clip

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**Serial Dilutions cont. Let’s try a serial dilution…**

Place a paper towel under your SEPUP tray. Using your pipet, put 10 drops of methylene blue into Cup 1.

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Serial Dilutions cont. Have 1 person from your group fill the other 8 wells with 9 drops of water. Add 1 drop of solution from cup 1 to the 9 drops of H2O in cup 2. MIX carefully using your pipet.

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Serial Dilutions cont. 5. Using a pipet, transfer 1 drop of the solution in Cup 2 to Cup 3. If you have any extra solution, return it back to Cup 2. MIX carefully using your pipet.

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Serial Dilutions cont. 6. Using a pipet, transfer 1 drop of the solution in Cup 3 to Cup 4. If you have any extra solution, return it back to Cup 3. MIX carefully using your pipet.

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Serial Dilutions cont. 7. Using a pipet, transfer 1 drop of the solution in Cup 4 to Cup 5. If you have any extra solution, return it back to Cup 4. MIX carefully using your pipet.

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Serial Dilutions cont. Continue this process through Cup 9, taking 1 drop of the solution from the previous cup and adding it to the 9 drops of water in the next cup. Create a Data Table like the following one in your LabBook

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Serial Dilutions cont. Cup Color Concentration 1 2 1/10 3 4 5 6 7 8 9

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Serial Dilutions cont. Record the color of the solution in each cup on your Data Table. Determine the concentration of the solution for each cup and record it on your Data Table.

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**Serial Dilutions analysis Questions**

Answer the following in your LabBook: What is the number of the cup in which the solution first appreared colorless? What is the concentration of the food coloring in this cup? Do you think there is any food coloring in cup 9? EXPLAIN.

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