Creating the blues with chemistry

This exercise is a part of Educator Guide: Beets Bleed Red, But Chemists Turn It Blue / View Guide

Directions for teachers: After your students read the online Science News article “Beets bleed red but a chemistry tweak can create a blue hue,” ask them to answer the following questions. A version of the story, “Beets bleed red, but chemists turn it blue,” can be found in the May 9 & May 23, 2020 issue of Science News.

1. What literary device is used to hook the reader? Paraphrase the information given.

The story’s lead uses rhyme, parodying the traditional poem “Roses are red.” Chemists took red pigment from beet juice and made it blue, so the resulting blue dye could possibly be used in consumable goods.

2. Why can’t chemists get natural blue colorings from certain blue animals for use in cosmetics and other products?

Chemists can’t get blue coloring from blue jays, butterflies and dragonflies because these animals don’t get their color from pigment molecules. The color is created through light scattering — structures on birds’ feathers and butterfly and dragonfly wings reflect blue wavelengths of light, so the feathers and wings are perceived as blue.

3. Why are natural blue pigments from foods, like blueberries, hard to bottle and use in cosmetics and other products?

Pigments from foods that are naturally blue, like blueberries, don’t last long so are not useful for creating shelf-stable blue products.

4. What is one technique that chemists use to adjust the colors of pigment molecules? Explain why the technique changes the color of the pigment molecule.

Chemists can change a pigment molecule’s color by adjusting the molecule’s chemical structure. The structural change alters the wavelengths of light the molecule absorbs and reflects, resulting in a color change.

5. How did chemists use this technique to create a blue dye from beets? Make sure to mention what molecules were used.

Beets get their reddish-purple color from a pigment molecule with alternating single and double bonds. To turn beet pigment blue, chemists removed a portion of the original molecule and added more of those alternating bonds with a compound called 2,4-dimethylpyrrole.

6. What did chemists do to test the dye’s durability? What were the results of those tests?

Chemists tested the dye under acidic conditions that cause many blues to fade or change color. The dye did not change color or fade in that test. The chemists also successfully colored fabric, yogurt and hair with the dye in lab tests.

7. Is the blue dye toxic? Is it safe for people to consume? Explain.

BeetBlue does not contain toxic metals. In lab tests, the dye was nontoxic to live zebrafish embryos and human cells. But many additional tests are needed to determine if the dye is safe to consume.