Science Buddies: "Ask an Expert"

My science project I'm doing is "How Sweet It Is: Measuring Glucose in Your Food" but there is one term I don't understand at all. It's how to make a dilution series and I'm confused on what it is, yet alone know what to do. I need someone to explain to me how to do it, so I understand it very easily. My science project is due in 2 weeks and I need to start doing the procedure. Thanks

Hi,

I think you are doing this excellent project from the Science Buddies website:

https://www.sciencebuddies.org/science- ... #procedure

The experimental procedure section suggests making a series of dilutions for a positive control. Starting with a 4% solution, you are supposed to dilute the sample in half, so you have 7 dilutions with the following concentrations of glucose 4%, 2%, 1%, 0.5%, 0.25%, 0.125% and 0.0625%.plus the negative control, which if pure water.

Here are the directions from the procedure:

Label seven cups 1–7.
Add 8 g of glucose to 200 mL water in cup #1 to make the 4% solution.
Add 100 mL of water to each of the six remaining cups (2–7).
Add 100 mL of the 4% solution to cup #2 to make a 2% solution.
Then add 100 mL of the 2% solution to cup #3 to make a 1% solution.

Let me describe the first dilution in detail to help you get started.

Your first cup will be 200 ml of water containing 8 grams of dissolved glucose
Your second cup is 100 ml of water

To make the first dilution, transfer 100 ml of cup 1 to cup 2 and mix well.
Cup 2 now contains ½ of the concentration of glucose compared to cup 1, or 2%. So you have made a one to two dilution.

Now repeat the procedure using 100 ml from cup 2 to transfer to the 100 ml of water in cup 3. Cup 3 now contains 1% glucose.

Does this help?

Donna Hardy

Hello somevesweet,

You are definitely not alone when it comes to confusion about how to make serial dilutions! I had a hard time understanding it when I was in school, but looking at a picture helped me. Here is a visual diagram of what Donna is talking about regarding making serial dilutions. Sometimes this idea is hard to visualize without a diagram.
http://biology.kenyon.edu/courses/biol0 ... ution3.htm

http://www.wikihow.com/Do-Serial-Dilutions

Does it make sense to you how to start with a 4% solution and go to a 2%, 1%, etc..?
1. A 4% solution means there is 4mL of solute (glucose) in 100mL of solution (in this case, water), so 4mL/100mL = 4%, the same as 0.04.

2. If you start with 200mL, how much glucose will you need?
--Back to algebra: the equation is X mL/200mL=4 mL/100mL.
--So x= 8mL glucose. (this information was already given to you, I'm just providing some background information for understanding)
Remember that when you make a serial dilution, the total amount in each tube should be the same, otherwise it is not a serial dilution. Each tube should have 200mL in it, according to the procedure.

3. if the [b]total volume needs to be 200mL [/b]and you know that in order to make a 4% solution, you need to add 8mL (the equation we just performed above),


You now have a 4% solution; use that for your next dilutions. After your calculation, add that amount from tube#1. You will always be taking 100mL from the previous tube in order to make your next dilution, and NOT adding more of the original 4% glucose.

Does this make sense? Let me know if you need clarification.