1. Colors of M & Ms and Skittles
Dr. Frank Walmsley
Trinity University
San Antonio, TX 78212

2. The Rainbow

3. The Rainbow As Seen by a Scientist
When the eye sees all the colors of the visible spectrum, it sees white light.

4. The Colors of M&Ms and Skittles The Dyes Used in Manufacture
Red Red
Blue Blue
Yellow Yellow
Green
Brown

5. Why are Red M&Ms Red?
A red object or a red solution is red because the eye sees the red light portion of the visible spectrum.
The other portions of the spectrum are absorbed by the object or solution and do not reach the eye.

6. A solution in a cuvette The colored solution is to be measured.
The colorless solution is a reference.
Light of varying wavelength pass through each solution and the difference is recorded.

7. A Red Solution
Some red color is dissolved from the coating of red M&Ms.

8. The Spectrometer
The visible spectrum from 400 nm to 700 nm is recorded by a spectrometer.
The spectrum shown on the screen is not the red solution.

9. The Spectrum
The spectrum of the red solution measured from 400 nm to 700 nm. Notice no light is absorbed from about 600 nm to 700 nm. This is red light.

10. This light not absorbed
This light absorbed

11. Why are Blue M&Ms Blue?
A blue object or a blue solution is blue because the eye sees the blue light portion of the visible spectrum.
The other portions of the spectrum are absorbed by the object or solution and do not reach the eye.

12. Preparation of a Blue Solution
Two M&Ms placed into water after about 5 seconds. Some of the dye is already dissolving.

13. A Blue Solution
A solution prepared by dissolving some coating from blue M&Ms as shown in previous slide.

14. Spectrum of Blue Solution
The spectrum of the blue solution from 400 nm to 700 nm. Notice that little light is absorbed between about 420 and 470 nm; this is blue light.

15. This light not absorbed
This light is absorbed

16. How Do You Get Green M&Ms without Green Dye?
Can you combine colors?
Which ones?
Right!
Yellow and Blue make Green

17. Preparing a Green Solution
Dissolving the coating from a yellow and a blue M&M. Notice the green solution forming.

18. A More Fundamental Question
WHY do yellow and blue make green?

19. Spectrum of Yellow Solution

20. Spectrum of Blue Solution

21. Blue Dye This part absorbed This part absorbed This part not absorbed
Yellow Dye
This part absorbed
This part absorbed

22. Yellow and blue make green
Because the yellow and blue dyes
absorb all the colors of light except green.

23. Brown is not a primary color.
It is a specific combination of other colors in specific quantities.

24. Preparing a Brown Solution
The coating from brown M&Ms is dissolved in water.

25. A Brown Solution
The solution from brown M&Ms appears sort of orange because of its low concentration.

26. Brown Solution Spectrum

27. A Black Solution How would you make a black solution?
What would the visible spectrum look like?

28. Think Green
Enjoy your M&Ms!

29. More Chemistry
What makes the dyes colored? How do they have different colors? Look at the molecular structures.

30. Structure of Red 40

31. Structure of Yellow 5

32. Structure of Yellow 6

33. Structure of Blue 1

34. Structural Analysis
Notice that these molecules have alternating single and double bonds from one end of the molecule to the other. This is a conjugated system.

35. Structural Analysis
This behaves as a single energetic system and the energy between the ground state and the first excited state is dependent on: 1. length of the conjugated system 2. the groups attached to the system

36. Structural Analysis
Start at the left sulfur and go to the right sulfur and see the alternating single and double bonds.

37. Structure of Blue 2