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

The Rainbow

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

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

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.

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.

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

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.

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.

This light not absorbed This light absorbed

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.

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

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

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.

This light not absorbed This light is absorbed

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

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

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

Spectrum of Yellow Solution

Spectrum of Blue Solution

Blue Dye This part absorbed This part absorbed This part not absorbed Yellow Dye This part absorbed This part absorbed

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

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

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

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

Brown Solution Spectrum

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

Think Green Enjoy your M&Ms!

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

Structure of Red 40

Structure of Yellow 5

Structure of Yellow 6

Structure of Blue 1

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.

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

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

Structure of Blue 2