Do You Do Serial Dilutions Every Day? (Probably)

What the heck is a serial dilution?

Here’s a simple example:

You know when you're doing dishes and cleaning out one of the water bottles you've probably been using for 5 days straight? You pop some water in it, a squirt of dish soap, then shake it like you’re in a 1980's Shake Weight infomercial... like Miss. Tiffany Cooper. Then rinse and repeat until the water isn’t soapy anymore.

Well this process is the same as doing serial dilutions (except in science, you wouldn’t discard all the soapy water....and you'd use a measuring device).

So, how can you do serial dilutions like a scientist? And what is the importance or purpose of doing serial dilutions?

First I’ll Get into the HOW, then we will dig into the WHY.

Materials you’ll need for your experiment:

• 5 jars with lids (preferably clear), other substitutes can be used!

• About ½ gallon of water

• 1 oz of liquid water flavoring concentrate (It needs to contain food dye! good examples of this are: Kool-Aid, Crystal light, or Mio)

• Something to measure ounces (oz) of water (cups can be used too, 1/8c =1oz)

• You can use a scale, a 1/8 measuring cup, or a device with a 1oz marking

Note: this experiment is substitution friendly!

- Don't have enough jars with lids?

Use a normal cup and mix with a spoon

- Don't have a measuring utensil?

Use anything you can get a uniform measurement with like a dixie cup, solo cup, etc...

- Don't have flavored water concentrate?

Use food coloring, it just wont taste like a whole lot of anything

The Experiment:

General Scheme:

1. Label each Jar 1 through 4

2. Fill up all the Jars with 9 oz or (1 ⅛ c)

3. In container #1, add 1 oz of flavored water concentrate

4. Pop the lid on and shake it up like Tiffany

5. Using your measuring device, take 1oz liquid from container #1 and place it into container #2.

6. Repeat step 4 for container #2

7. Using your measuring device, take 1oz of liquid from container #2 and place it into container #3.

8. Repeat step 4 for container #3

9. Using your measuring device, take ⅛ of a cup of liquid from container #3 and place it into container #4.

10. Shake it up one more time, and then observe! your color variants should look similar to the image below

Now it is time to observe your experiment!

• How significant is the color change between the liquid in Jar #1 compared to Jar #2? What about Jar #3 and Jar #4?

• Taste the liquid in each Jar, which container tastes the most like your flavor concentrate? Which one tastes the least like the flavor concentrate?

Now why is this process important in science?

#1. This experiment uses 37 oz of water in total (almost 5 cups). If you were going to try to make a solution that is the exact same composition as what is in Jar #4 without performing serial dilutions, you would have had to use 1 oz of your flavored water concentrate, and 37,000 oz of water. That would produce a LOT of waste!

#2. It’s efficient! Imagine measuring out 37,000 oz of water… I can’t.

#3. Most serial dilutions are done using a logarithmic scale (base 10) like we did in this experiment, i.e. Jar #1 is a 1:10 dilution, Jar #2 is a 1:100 dilution, Jar #3 is a 1:1000 dilution, and Jar #4 is a 1:10,000 dilution. If you were to make a graph of this or analyze the data, it would be pretty darn easy! Using this numerical scale is easy to process and digest for scientists when we are performing observations, just like you did at the end of your experiment!

What are Serial dilutions usually used for:

• Determining how many bacteria are in a sample. Below is an example of a serial dilution that was performed on agar plates.

• Diluting expensive products so they are not wasted. Some of the products we use in research can cost over $1000 for a single gram or ml of product! Sometimes more! Below is a immunotherapy (anti-cancer) drug that costs over $2,590 for a single mL. For reference 30mL= 1oz, 1 oz of this drug would cost $77,700!