The September STEM Like a Girl Challenge of the Month is a sweet one! This month we explore how crystals form by making your own Candy Crystal Lollipops.
Background
A crystal is a solid material whose atoms, molecules, or ions are arranged in a highly ordered microscopic structure. Think about how frost forms on your car windows when it’s cold out. Liquid water from the air crystallizes in the cold weather to form solid water in a ordered pattern. This process starts with the formation of a small crystal that grows and combines with other ice crystals until you have one large sheet of crystal ice on your window.
Rock candy is made in a similar way except the crystals are made out of sugar instead of water. Each grain of sugar is made up of trillions of sugar molecules that are held together in a regular pattern. When you dissolve sugar in water over heat, these molecules break apart to form a solution. As the water cools and evaporates, the dissolved sugar becomes more concentrated and the sugar molecules move around in the solution. When they collide together, the crystallization process starts. Over time, more and more sugar molecules join the growing crystal and the end result is a tasty sugar crystal lollipop!
This experiment takes some patience as the crystallization process takes several days. Observe your growing crystals daily to see how they are changing.
Materials
- 4 cups granulated sugar (plus a little extra to coat the sticks)
- 1 cup water
- Lollipop sticks, skewers, or popsicle sticks
- Cups
- Clothes pins
- Food coloring (optional)
- Candy Crystal Experiment Test Sheet
Methods
- Download and print the Candy Crystal Experiment Test Sheet.
- In a small sauce pan, heat the water.
- Slowly add in the sugar and stir until it is completely dissolved.
- Allow to gently boil for a couple minutes and then cool slightly.
- While the sugar solution is cooling, dip one end of each stick into the solution and then roll it in a little bit of granular sugar (Picture 1). The new crystals need an existing crystal to form on, called a seed. The new crystals will grow only where you have coated your stick. Allow the coated stick to fully dry.
- Once the sugar solution has cooled some and is safe to pour, fill each of your cups.
- If using, add a few drops of food coloring to the solution. Leave one clear so you can really see the crystallization process happen.
- Gently place the coated end of your sticks into the sugar solution and use a clothes pin to secure it at the top (Picture 2). **IMPORTANT** Make sure the sticks aren’t touching the bottom or sides of the glass. If it is touching anything, crystals will form between the two surfaces making it very difficult to remove the lollipop.
- Place your cups in a location they won’t get bumped and let them sit still for several days. You can lightly tent some plastic wrap over the tops of the glasses to keep dust out.
- Observe your rock candy every day to see how it’s changing and growing (Picture 3). Be careful not to disturb it too much.
- When your crystals are big enough (or your patience runs out!), gently remove the lollipops from the glass. Ours pictured below were removed after 3 days. If a hard layer of crystal has formed on the top, carefully break through it so you can remove the sticks.
- Allow to dry and enjoy your sweet science treat! (Picture 4)
We’d love to see pictures of the Candy Crystal Lollipops you create! Email your pictures to info@stemlikeagirl.org to be featured on our website or social media. Or you can tag us on instagram @stemlikeagirl_pdx or use the hashtag #stemlikeagirlchallengeofthemonth
