Name:______________________________________________ Assignment #: _____
A Kool Drink on a Hot Summer Day
Solution Concentration Lab
Background
You’ve probably made a refreshing drink from a powdered drink mix such as Kool-Aid on a
hot summer day. Parents often try to make the drink less sweet by adding less sugar or sweetened
powder to the water. Often they add more water. In other words, they water it down, or dilute it.
In this activity, you will prepare different concentrations of Kool-Aid using a technique
called serial dilution. This method takes a portion of a concentrated solution and dilutes it in
several containers in succession. Each prior dilution becomes the source of solution for the next
dilution. It can provide better accuracy in measurements, especially when making a diluted solution
from a much more concentrated solution.
You will then use an instrument known as the SpectroVis plus which can measure how
much light is absorbed by each of your dilutions. You will discover that there is pretty simple
relationship between concentration (molarity) and absorbance. The data that you will collect will
allow you to generate a standard curve which can be used to calculate the concentration of any
reddish Kool-Aid unknown.
Sample Preparation
You will need: a 100-mL plastic beaker, four paper cups, a 25 or 50-mL graduated cylinder, KoolAid or other presweetened powdered drink mix, glass stirring rod, pipette, deionized water,
SpectroVis Plus, one cuvette, and cuvette wipes.
NOTE – Think about the possibilities for contamination throughout this lab and rinse all
shared equipment before using it between one step and another.
1. Measure out 2 grams of Kool-Aid drink mix into your 100-mL plastic beaker.
2. Add DI water to the beaker until the solution reaches the 50 mL mark. Stir the solution until all
the Kool-Aid is completely dissolved. This is your “Cup 1”.
3. Take 25 mL of solution from Cup 1 and place it in a paper cup labeled “Cup 2”. Add 25mL of
water to Cup 2 and stir. Observe and record the intensity of the color.
4. Take 25 mL of solution from Cup 2 and place it in another paper cup labeled “Cup 3”. Add 25mL
of water to Cup 3 and stir. Observe and record the intensity of the color.
5. Continue with the dilution method through Cup 5. This will produce five cups of drink mix
solutions with varying concentrations.
Cup
1
•4 g KoolAid
•50mL
volume
Cup
2
•25mL
Cup 1
•25mL
H2O
Cup
3
•25mL
Cup 2
•25mL
H2O
Cup
4
•25mL
Cup 3
•25mL
H2O
Cup
5
•25mL
Cup 4
•25mL
H2O
Name:______________________________________________ Assignment #: _____
Sample Testing
6. Make sure SpectroVis Plus is plugged into USB port of Labquest. There should be a red window
that says USB: Abs. Make sure mode is in “full spectrum”.
7. Carefully pour some of the Cup 5 sample (Important: Use most dilute sample first!) into a
clean cuvette so that the cuvette is ¾ full. Always hold cuvette by ridged side. The clear side
will be where light shines through the sample. Place cuvette into SpectroVis Plus such that
clear end is facing arrow symbol.
8. Hit green run arrow in lower corner of LabQuest. Hit discard if it asks you to save latest run.
The program will run a few seconds and a graph of your sample versus wavelength will pop up.
Hit the red square in corner to stop.
9. The program automatically selects the highest peak or maximum absorbance. The absorbance
number is located near the upper right hand corner of window. Record this absorbance for cup
5 in the table below. Even though we won’t use the wavelength for any calculations, record that
in table as well. This number can be found in lower right hand corner of window.
10. Discard sample from cuvette by shaking it out into sink. Make sure there is no water in cuvette.
11. Repeat steps 7-10 for next 4 samples starting with sample 4, then 3, etc.
12. Go to back table and put unknown Kool-Aid mix in your cuvette. Get its absorbance reading
from SpectroVis Plus and record value in data table.
13. Rinse all Kool-Aid samples down sink. Clean all other Kool-Aid contaminated labware and leave
materials out for next lab section.
Data Table
Cup
Number
Color Intensity
(qualitative)
Wavelength
(nm)
Absorbance
(y axis)
Molarity (you
must calculate)
(x-axis)
1
2
3
4
5
Unknown
Interpret from your
graph
Name:______________________________________________ Assignment #: _____
Questions
(Note questions 3 and 4 are part of graph)
1. The major ingredient in Kool-Aid is sucrose, C12H22O11. If we assume the molar mass of sucrose
is the molar mass of Kool-Aid, calculate the molarity of the starting solution in Cup 1 of this
experiment. (1 pt) (SHOW CALCULATIONS TO GET CREDIT!!!)
2. For Cups 2-5, you created a diluted concentration of the previous cup. Calculate the molarity of
Cups 2-5 and explain how you determined that concentration. (4 pts) (SHOW CALCULATIONS
TO GET CREDIT!!!)
3. Create a graph (either in Excel or by hand) showing the molarity vs. the absorbance reading.
This is your standard curve. (5 pts.) (Make sure graph has all correct labels, title, etc.)
4. Using your graph, plot the absorbance value of the unknown sample and determine the
concentration of the unknown. (2pts) (Need to show on graph!)
5. What do you think the absorbance of a solution tells you about the solution? Did the absorbance
increase or decrease as the concentration got smaller? Why? (2pts)
6. Why is it important to use the most dilute sample first? Be thoughtful with your answer. (2pts)
7. Where was the average wavelength that these solutions had their maximum absorbance? What
color of the visible spectrum is this? (2 pts)
8. You may have noticed that these red solutions showed no absorbance in the red part of the
visible spectrum. Why was this the case? (1 pt)
9. At what wavelength would you predict blue raspberry Kool-Aid to have its highest absorbance?
(1 pt)
Your final report should have your name and title followed by …
 Electronic data table
 Full Page graph
 Answers to questions in complete sentences (separate page) You can leave space and write
your calculations for questions 1 and 2 in pencil.