How to Grow the Best Crystals
IntroductionHave you ever wondered how crystals are made? Crystals come in all different shapes and sizes. However, the purest and cleanest crystals are usually also the ones that grow to be the largest in size. In this activity, you will compare the size and shape of crystals grown at different temperatures. With just water and Borax, a household cleaning product, you can discover the method for growing large, pure crystals!
- Pipe cleaners (2)
- Pencils (2)
- Borax, also called 20-Mule Team household cleaner. It can be found in the cleaning aisle of many grocery stores.
- Measuring tablespoon
- Large bowl
- Identical jars or large drinking glasses (2)
- Cooking pot
- Plastic wrap
- Ice cubes
- Like many other household cleaners, Borax is harmful if swallowed, inhaled, or contacts eyes, and on rare occasion touching Borax can result in rashes. Caution and adult supervision is advised when handling the Borax
- Fill a large bowl half full of ice cubes and then add water until the bowl is about three-quarters full. Set this bowl aside for now. If needed, adjust the water level in the bowl so that when you put a jar in it, the water reaches at least two-thirds the way up the jar, but is not so high that it goes into the jar.
- Twist a pipe cleaner around each of the two pencils. Adjust the pipe cleaners' lengths so that when the pencil is laid across the top of one of the jars or large drinking glasses, the end of the pipe cleaner hangs down to just above the bottom of the jar. Make the pipe cleaners equal lengths. You can shape the dangling end of the pipe cleaners in to interesting shapes if you prefer.
- Fill a cooking pot with enough water to fill both jars nearly full. Then bring that water to a boil on the stove. Once the water is boiling, turn the burner off so that the water is no longer boiling. Borax is harmful if inhaled or contacts eyes, so it is advised to not use boiling water when dissolving the borax.
- Add 1 tablespoon (Tbsp) of borax to the water and stir until it dissolves. Continue to add 1 Tbsp at a time until no more dissolves. You will probably need about 3 Tbsp of borax for each cup of water.How does the liquid look now? Is it still clear? What happens to the little bits of Borax that won't dissolve?
- Carefully pour equal amounts of the Borax solution into the two jars. Each jar should be about three-fourths full.
- Lay a pencil across the top of each jar so that the pipe cleaner hangs down into the solution.
- Cover the top of the jars with plastic wrap.
- Leave one jar undisturbed on a countertop or table at room temperature. Place the second jar in the bowl full of ice that you prepared. Make sure the water level in the bowl reaches at least two-thirds the way up the jar, but is not so high that it goes into the jar.
- Do not disturb the jars for at least five hours. Check the bowl of ice regularly and add ice if it has melted.
- Check on the jars about once an hour to see how the crystals are forming. It may be difficult to observe the jar in the bowl — try looking at the pipe cleaner through the plastic wrap cover.Do you see crystals forming on the side of one of the jars? Do crystals form in one jar before the other?
- After five or more hours, carefully remove the pencils and observe the crystals on the pipe cleaners.How do the size, shape, and number of crystals on each pipe cleaner compare to each other? Why do you think this is?
- The extra Borax solution can be poured down the sink.
- To get rid of crystals stuck on the sides of the jars, wash the jars in very hot water.
You should have observed that the jar kept in ice water has more crystals, but those crystals are smaller in size. In contrast, fewer crystals grow in the room temperature jar but those crystals are bigger and have a more cube-like shape.
As the hot mixture of Borax and water cooled, the Borax was forced out of the liquid mixture. This Borax turned into crystals. A crystal is made up of the smallest units of a substance (called molecules) that have come together to make a specific pattern that gets repeated over and over, to make a pattern. Not only do the Borax molecules have to get close enough to each other to make the crystals, but the molecules also have to fit together in the right way to make the crystal pattern. How the molecules interact with each other to make the crystals is affected by temperature, as you should have seen in this activity.
Chemical reactions are constantly happening all around you, and inside of you. As just one example, a chemical reaction can turn metal into reddish-brown rust (specifically, the iron in the metal is reacting with the oxygen in the air or water). Chemists perform chemical reactions to change one chemical into another. Sometimes multiple products are formed and the chemist may want to separate one from the others. One way this can be done is using a process called recrystallization. In recrystallization the mixture of products can be dissolved in hot water and then cooled. As it cools, one product appears as crystals, which are removed from the rest of the liquid, which has the other product.
Why do crystals appear as the mixture cools? It has to do with solubility, or the largest amount of something that can be dissolved in something else, such as dissolving Borax in water. The solubility of most solids increases with temperature. In other words, more Borax may be dissolved in hot water than cold water. So if a hot, saturated mixture is cooled, there is more Borax than can be contained by the colder water, and so Borax may come out of the mixture, forming crystals.
When the molecules come together to make the crystal, things other than these specific molecules do not fit well into the crystal structure, much like the wrong piece of a puzzle does not fit. If the crystals are allowed to form slowly, the molecules that do not fit in the crystal structure will be kept out of it and will instead remain in the water. But if a solution is cooled too quickly, there is not time to reject the impurities and instead they become trapped in the quickly-forming crystal structure and disrupt the pattern.
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For Further Exploration
- In this activity you examined Borax crystal formation at two different temperatures, but you could try other temperatures as well, such as by sticking one of the jars in the refrigerator. How does allowing the Borax mixture to cool at a different temperature affect crystal formation?
- Try making crystals out of other materials, such as sugar or salt. How well do crystals form using other mixtures with water?
- You did this activity for at least five hours. How do your results change if you grow your crystals for a longer period of time? Make sure to keep adding ice cubes to the water bath to keep it cool throughout the activity.
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