ChemixaLEARN CHEMISTRY

Candy dye chromatography

Objective: use paper chromatography to separate the dye mixtures in candy coatings and felt-tip markers. You will spot samples on paper, develop the chromatogram in water, and explain the separated bands with differential attraction to paper and water.

Safety:

Use only washable markers and food candies; permanent markers contain solvents that are unsafe for this activity. Food dyes can stain clothes and surfaces, so work on a covered table. Adult supervision is required for minors.

Materials

  • White coffee filters or paper towels
  • Brown and green candy-coated chocolates
  • Washable felt-tip markers
  • Clear cup
  • Water
  • Pencil
  • Ruler

Procedure

1

Prepare paper strips

Cut a coffee filter into strips about 2 cm wide and draw a pencil line 2 cm from the bottom of each strip.

2

Spot the samples

Dissolve the colored shell of a candy in a few drops of water and dab the concentrated color onto the pencil line, or make a small dot with a marker.

3

Prepare the developing cup

Pour a shallow layer of water into the cup, about 1 cm deep.

4

Develop the chromatogram

Hang each strip so its bottom tip touches the water but the sample dot stays above the waterline.

5

Wait and dry

Wait 10 to 15 minutes as water climbs the paper, then remove the strips and let them dry.

6

Compare the bands

Compare the separated bands from different candies and markers and note which dyes traveled farthest.

What to observe

  • A brown candy dot separates into two or three distinct color bands.

  • Different marker colors climb to different heights.

  • Water rises up the paper carrying the dyes with it.

  • Each dye stops at a consistent height for that dye.

Why it happens

Chromatography separates mixtures because different substances stick differently to two phases: a stationary phase and a moving mobile phase. Here the paper is the stationary phase and the climbing water is the mobile phase. Each dye is carried upward at its own speed depending on how strongly it clings to the paper fibers versus how readily it dissolves in the water. A dye that loves water races ahead; one that grips the paper lags behind. That is why a single brown candy dot splits into separate colored bands: the brown was a mixture of dyes all along, and chromatography unmixes them.

Try variations

  • Test whether two brands of brown candy use the same dye mixture.

  • Try salt water as the mobile phase and compare the separation.

  • Measure how far each band traveled relative to the water front.