Wikijunior:Big Book of Fun Science Experiments/Grow your own crystals
In this experiment, you can make crystalline rock candy that you can eat! It takes 4-7 days.
Crystals form from a solution when molecules of the dissolved solid (in this case, sugar) come together and fall out of solution to form clumps. This process is called nucleation. You can speed up this process by introducing something solid into the solution for the crystals to begin to form on. This is called assisted nucleation.
As with all experiments, you should consult an adult before starting. This experiment involves:
- Very hot water - This can burn your skin. You should get help from an adult when boiling water, moving and pouring it.
- You will be putting boiling water into a container. Some glasses shatter when they heat up suddenly, so you will need to choose a container such as a jar, jug or mug that is designed for tea or coffee or hot jam, rather than one designed for cold liquids. A glass mug is best, because you will be able to see the crystals as they form.
- Food colouring - You can use this to colour your crystals, if you want. However, food colouring stains clothes, counters and skin. You should wear an apron if you use food colouring. Wipe up any spills immediately.
What You Will Need
- A very clean mug that can contain hot liquids
- A jug or saucepan with a pouring lip that can contain hot liquids
- A long piece of clean cotton string or thread
- About 3 cups of sugar
- About 1 cup of very hot water
- A support stick, such as a pencil or a chopstick (Hexagonal or rectangular prism to stop it rolling off)
- A paper clip or another similar small weight
- Paper towel
- Food colouring (optional)
- Tie the string to the pencil/chopstick. When you place the chopstick across the rim of the jar/mug it should hang down into the jar. The string should be just long enough to almost touch the bottom of the container.
- Tie the paperclip to the dangling end of the string. This will act as a weight holding the string in place.
- Boil the water. Remember, boiling water is very dangerous!
- Carefully pour the liquid into a saucepan or jug which you can pour from.
- Add a tablespoon of sugar and stir until the sugar dissolves (disappears).
- Add another tablespoon and stir again.
- Repeat this until the sugar stops dissolving. You will be able to tell because the sugar will remain at the bottom of the container. This is called a saturated solution.
- If you want coloured sugar crystals, add a few drops of food colouring. Remember to wear an apron!
- Carefully pour your solution from the jug into your mug or jar. If you have undissolved grains sugar in the bottom of your container, avoid getting them into the mug or jar.
- Put the pencil/chopstick across the rim of the mug so the string hangs down into the solution and the paper clip lies on the bottom in the middle of the container.
- Cover your jar with a piece of paper towel to stop dust from falling in.
- Using oven mitts if you need to move the jar, carefully put it somewhere safe.
- Wait 4-7 days.
Even though your crystals will take 4-7 days to completely form, you should be able to see the beginnings of the crystals after a day or two.
- Remove your string, now covered in little sugar crystals
- You can let your candy dry on a plate or you can eat it right away.
In this experiment you make a saturated sugar solution. There are a lot of sugar molecules dissolved in the hot water. After the water has cooled and evaporated a little, the molecules become closer together. As the sugar molecules touch the string, they attach to it and fall out of solution. As more molecules do this, they start to arrange themselves in an organized network. These organized networks of de-dissolved sugar molecules are sugar crystals.
You can see this process in the natural world. Rocks such as granite are formed when liquid rock, or magma, cools very slowly in chambers underground. As the magma cools, minerals in the rock begin to slowly recrystallize, just as the dissolved sugar recrystallized. When you look at a piece of granite it looks speckley in black, grey and pink. Each speckle in a granite is a crystal, grown over thousands of years.
How Crystals Form - A more detailed explanation of how crystals form from solutions.
Video Instructions for Rock Candy - A video of a scientist performing this experiment.