Home Science Activity: Skittles Rainbow
A little bit of colourful chemistry, a bit of art and a lesson in density and concentration gradients.
Yeh, you will need a lot of skittles, but it is all for science.
Learning Intentions
Students will examine and be able to describe/understand the following:• What happens when materials are mixed• The solubility of common materials in water• How density affects liquids• The difference between solutes and solvents.
Overview
You will make a hypothesis (a prediction) about what you think will happen. Try to give reasons foryour hypothesis.
Write down everything you observe while doing each experiment. You might like to draw a picture.
Discuss your findings with your class. Was your hypothesis supported? Did anything happen thatyou didn’t expect? Can you explain what you have observed? What difficulties did you run into?
The tables for each experiment are found at the bottom of this worksheet.
Hypothesis
Skittles have a coating of sugar mixed with food dye to give them their different colours. Inexperiment 1 you are going to see what food dye alone does in water. Use what you observe here
to infer what you think will happen in the following experiments where you use skittles. Refine yourhypothesis as you work through each experiment. There is a place in each experiment’s table towrite your hypothesis.
Materials• White bowl or plate, slightly slanted towards the centre (paper plates should work well)• Skittles• Water (warm water will work best, but cold water is fine)• Food dye (any colour)• Eye dropper or pipette (A straw works OK also – just insert into liquid and hold the top.)
Teacher Notes

Teaching Notes: Running the activity

What is happening:
What is happening: Skittles are coated withsugar and food colouring, which dissolve inthe warm water. You should have observedthat the colours don’t mix as they run down
the plate. See Figures 1 and 2 below.

MethodIf you are doing this as part of a class activity,
work in groups of 2-3 students.

The explanation for this is can be found by
understanding concentration gradients.

Notes: In each experiment, it works best if yourplate is on a level surface.

Chemicals or molecules will move (diffuse)from an area where they are in highconcentration to an area of lower
concentration. This is known as theconcentration gradient. In our case, we havethe food dye and sugar (the solutes)
dissolved in the water (the solution). The
sugar/dye dissolve from the Skittle and are ina high concentration immediately around theskittle. The solutes (sugar/dye) will want tomove to areas of lower concentration, which
will be toward the middle of the plate, orwherever there is lower concentrations ofsugar, which will initially be away from theskittle. See Figure 3 below.

Experiment 1. Dye only
Method: In your bowl/plate place enough water toalmost fill the plate or about 0.5 cm in your bowl.
Make sure the water is still. Use the pipette/eye
dropper/straw to place one drop of food colouringin the middle of the water. What happens to thefood dye? Complete Table 1.

Experiment 2: One colour at a time
Method: Place a skittle in a bowl or plate, and add
water until the skittle is submerged. Observe what
happens over the next 2-3 minutes. What
happens if you add multiple skittles of the same
colour into the middle of a bowl of water? What
will happen if you then add more water? Compare
this to the food dye in experiment 1. Complete
The different colours of each do not mix when Table 2.
they meet because the sugar concentrations
Experiment 3: Mixing colours
are roughly equal for each skittle. Thisappears as a boundary between each colour Part A:
Method: Carefully place a yellow and a red skittle
because there is no gradient or difference inon opposite sides of the bowl, or at least 4cm
solute concentration. That is, the sugar (andapart. Add a layer of water to submerge thedye) just stop moving when they reach askittles. Observe what happens over the next 2-3
sugar concentration that is equal. Instead
minutes. Write your observation in Table 3(a)they continually move (a process calleddiffusion) to where the sugar concentration isPart B:lower. If you have the opportunity, leave theMethod: You should observe that your two colours
plate overnight and check it again the next
meet in the middle of your bowl and form aday. Do the boundaries between the colours
boundary. Why did the boundary form and thestill exist?
colours not mix?
Adding sugar: When you add sugar to theNow place a 1/4 teaspoon of sugar in the middle
middle, you should have observed thedifferent colours moving away from the sugar. where the two colours meet. Again, before you do
this write what you predict will happen when theWhat you have done is place a sugar
sugar is added. Write your observations and what
concentration in the middle of your colours
you think is happening in Table 3(b).
that is a lot higher in concentration than thesugar in each of the colours. The sugar you
added – being of highest concentration – will Experiment 4: Making a rainbow
want to move to areas of lower concentration, Method: In a clean bowl, place skittles around theedge, close to each but not quite touching (thoughwhich is away from the middle of the plate
you will get an effect however you do it). You
where you put your sugar.
might like to place them in rainbow order (red,orange, yellow, green, purple). Add warm water
Rainbow in glass: This experiment can be
until the skittles are partially submerged. Watch
explained by understanding density. Whatyou should have observed is that the different what happens over the next few minutes. Write
skittle colours form layers in the glass.

Remember that when you add water to theskittles that the sugar and dye in the Skittle
coating dissolve into the water. This meansthat the glass with the most skittles (purple)
will have a higher amount or concentration ofsugar dissolved in the water. The glass withthe fewest skittles (green) will have thelowest concentration of sugar in the water.
Water with a higher amount of dissolved
material will be denser than water with lower
amounts of dissolved material. That is, themore solute or dissolved particles in asolution, the higher the density of thatsolution. In our case, purple with the highest
amount of sugar dissolved in the water will be
the densest solution. The green solution, withthe least dissolved sugar will be the solution
with the lowest density. A liquid with a lower
density will float on a liquid of higher density.
Because you added the liquids in an order ofhighest density to lowest density, you shouldhave achieved a rainbow with a purple layer
at the bottom, then a layer of red, thenorange, then yellow and at the top, green. If
you had time to add the colours in thereverse order, you should observe that thecolours mix together because you keep
adding a denser liquid onto a less dense
liquid, which means it will want to head forthe bottom and in the process mix the twosolutions together to become one.
Should the Making a Rainbow experimentprove too tricky for students, a simpler
FLEET home science experiment thatvisualises the concept of liquid densities
more explicitly is Layered liquids.
Temperature also affects density. Try
FLEET’s home science experiment, Floating
water
Other FLEET home science experiments that
explore density are the following:
Coke V diet cokehttps://www.fleet.org.au/blog/coke-vs-dietcoke/your observations and what you think ishappening in Table 4.
Get arty: Try arranging the skittles in different
patterns and make some cool art. Place themcloser together, further apart.
Extension 1: Other colourful foods
What other lollies or foods can you think of thatmight also work? Have you got anything else in
the house you can try? What happens if you use
cold water instead of warm/hot water? Write yourobservations in Table 5.
Extension 2: Rainbow in a glass
This can be tricky to get right and you need tomake sure the sugar has nearly all dissolved fromthe skittle coating. This might take 5 minutes ormore. Warm water will work quicker. If you areshort on time. You also need a steady hand when
adding each layer, which is sometime difficult for
the younger kids.
Additional materials:
5 glasses/bowls (any shape)
1 clear glass or cup (close to cylindrical ifpossible)
A pipette or eye dropper (a straw will work OKalso)
MethodIn glass 1, place 10 purple skittles
In glass 2, place 8 red skittles
In glass 3, place 6 orange skittles
In glass 4, place 4 yellow skittles
In glass 5, place 2 green skittles
Add two tablespoons of water to each glass, andstir. Wait for the skittles to completely dissolve.
Pour the purple water into the cylindrical glass,then use the pipette to very gently transfer the redwater into the glass. It works best if you hold thepipette against the side of the glass near thesurface of the liquid in the glass and pipette theliquid against the glass. Continue doing this withthe orange, then yellow and then green. Make
sure that the colours don’t mix together as you
add them. If you have time repeat the experimentDancing sultanas https://www.fleet.org.au/blog/dancingsultanas/
Lava lamp https://www.fleet.org.au/blog/lava-lamp/and add the colours in the reverse order. Do you
get the same effect? Write your observations andwhat you think is happening in Table 6.
Some reflection
Discuss with your group what you observed. Did
your hypotheses get more accurate with eachexperiment? What did you learn? How did yourhypotheses and learning compare to othergroups?

Acknowledgement: This activity was developed by Andrew Groszek, a FLEET
research fellow at the University of Queensland.
ImagesFigure 1. The sugar/dye will diffuse from areas of high concentration to areas of low
concentration. A boundary is formed where the colours meet because the sugar/dye
concentrations will be similar and they therefore tend not to mix

Figure 2. Get creative. Because there is no gradient at the boundaries of the colours
they tend not to mix and you can arrange the Skittles in creative patterns to create
amazing art. See what happens, however, when you leave the plate overnight.

Figure 3. Sugar and dye molecules will diffuse (move) from where they are in highconcentration to areas of lower concentration.

The relevant tables for each experiment are on the following pages

Results Tables
Table 1. Experiment 1 Dye only
Hypothesis (What will happen to the food dye?)Observations (Draw what you see)Discussion (What is happening?)

Table 2 One colour at a time
Hypothesis (What will happen to the skittle when you add the water?)

Observations (Draw what you see)Discussion (What is happening?)

Table 3 Part A Mixing colours
Hypothesis before and after sugar is added. What will happen when you add water?

Observations before and after water is added (Draw what you see)Discussion (What is happening? Why did the colours not mix in Part A.)

Table 3. Part B Mixing colours
Hypothesis (What will happen when you add the sugar?)Observations (after sugar is added)

Discussion (What is happening?)

Table 4. Making a rainbow
Hypothesis (What will happen when you add water?)

Observations (Draw what you see)Discussion (What is happening?)

Table 5. Extension 1. Other colourful foods, different water temperatures
Hypothesis (What happens with different water temperatures?)

Observations

Discussion (What is happening?)

Table 6 Rainbow in a glass
Hypothesis (What will the result be as you add the different coloured liquids? Think
about what is different about the contents of each glass and how this might affectwhat is happening)

Observations

Discussion (What is happening?)