Presentation from the eTwinning STEM Featured Group Learning Event in the frame of the STEM Discovery Week

1. The Chemistry behind jelly beans
Céline Laugel
Lycée Marguerite Yourcenar, Erstein, France

2.  Context
 Material
 Smurf solution
 Beer’s law
 Calibration line
 Analysis and results
 Comments
Plan

3. Idea : using knowledge and know-how in
spectrophotometry to answer a surprising and
funny question:
« How many smurfs candies can you eat in one
day without exceeding the acceptable daily intake
for patent blue V ? »
Prerequisite :
Beer’s law in spectrophotometry
experimental process to find out the concentration
of a coloured solution
Age : students in highschool (in France, pupils
aged 16-17)
Time for the experimental work: 1h30 – 2h
Context

4.  For each group of pupils:
one smurf candy and scissors;
a 100 mL Pyrex beaker
distilled water
a stirring rod
a hot plate
a 500 mL volumetric flask and its stopper
a plastic pipet
a 50 mL beaker
a test tube and its stopper
 On the teacher’s laboratory table:
A graduated buret containing a stock solution of patent blue V (E 131 food colouring),
mass concentration c = 5.6 mg/L
A graduated buret containing distilled water
A spectrophotometer
Transparent cuvettes and plastic pipets
Material

5.  Cut off the cap of a smurf candy, to keep only the
blue part of the body.
 Put the smurf into a 100 mL Pyrex beaker, add
about 30 mL of distilled water and heat it
 Keep on stirring the solution until the candy is
completely dissolved.
 Transfer it into a 50 mL volumetric flask.
 Add distilled water up to the calibration mark,
plug and shake.
The prepared solution, called smurf solution, is blue
and contains the quantity of patent blue V
contained in ONE smurf candy.
smurf solution

6. .
A spectrophotometer is a device that measures the intensity of the light getting through a
coloured solution: more precisely, it measures the intensity of the light before and after
having gone through the solution and calculates a quantity called absorbance A (no
unit).
Absorbance depends on several parameters. We can use Beer’s law, which states that
absorbance and concentration are proportional:
A = k c (k being a constant)
Plotting A versus c leads to a line and gives us the link between the absorbance of patent
blue V and its concentration in solution. This line is called calibration line.
Beer’s law

7.  Preparation of the dilute
solutions of patent blue V
Prepare dilute solutions of patent
blue V using stock solution .
A volume of 10 mL of each dilute
solution is enough for measurements
using the spectrophotometer.
 Absorbance measurements
Each group measures the absorbance
A of the dilute solution they have
prepared .
All these measurements will help plot
the calibration curve .
Calibration line

8. Analysis and results (1)

9.  mass of patent blue V in one candy:
smurf solution just one candy.
mS = cS × V = cS × 0.050
Example: mS = 6.6 × 0.050 = 0.33 mg
The mass of patent blue in one smurf candy
was 0.33 mg.
 number of candies that can be eaten safely:
acceptable daily intake (ADI) for patent blue V:
2.5 mg per kg of bodyweight per day.
for a 60 kg person, the ADI is 2.5 × 60 = 150 mg.
Example:
150 / mS = 150 / 0.33 = 450 candies.
One pack of candies contains about 40 candies, so
450 candies would stand for about 11 packs!
Analysis and results (2)

10.  When using inquiry process?
• to identify the food colouring (absorption spectra of several chemicals such as cupric
sulfate, indigotine, bromothymol blue and patent blue V)
• to « extract » patent blue V from the candies
• to plot a calibration curve, having chosen proper dilute solutions
• to dilute a stock solution
•to choose and set the appropriate wavelength on the spectrophotometer
 No spectrophotometer in your lab ?
Try smartphone application « Color Grab »
More about this app on the website of Science on stage (guide iStage 2: Smartphones
in Science Teaching: https://www.science-on-stage.de/download_unterrichtsmaterial/iStage_2_-
_How_deep_is_your_blue_IMP.pdf
Comments (1)

11.  Want to know more about this experiment?
Go on the dedicated webpage on etwinning:
https://twinspace.etwinning.net/10057/pages/page/256621
Everything is described in the TIPS guide Chemistry.
Any comment, question?
Contact me :
celine.laugel67@gmail.com
Comments (2)

12. Thank you for listening
and see you !