This post is part of the 31 days of STEM activities for kids series. If you’re checking in for the first time, visit here for the rest of the series!
We’re slowly working our way through all the classic science experiments for kids. Epsom salt crystals are a classic experiment everyone should try at least once!
You’ll also want to check out the ultimate list of summer STEM activities and the ultimate list of summer science experiments.
Epsom Salt Crystals Science:
Epsom salt is another name for magnesium sulfate. When water is heated, it can hold more magnesium sulfate. When you heat water and stir in Epsom salt, the water absorbs the salt.
However, when the mixture is refrigerated, the magnesium sulfate atoms pull away from the water and form a crystal structure because the water can no longer hold all of the Epsom salt.
Epsom Salt Crystals Experiment:
- Epsom salt
- Food coloring
- Something for the crystals to “stick” to (we used some toast crumbs)
- Container for the Epsom salt crystals
Stir about 1/2 a cup of Epsom salt into 1/2 a cup of hot tap water (but not boiling).
Tap water is better than filtered water for this project because more impurities make better crystals. Not all of the Epsom salt will absorb, but most will.
Add some food coloring and a few pieces of impurities (you don’t have to use toast crumbs) and pour it into your container.
Stick the mixture in the freezer for about 10 minutes to rapidly cool, then stick it in the refrigerator overnight.
The Results:
The next morning, you should see that crystals have formed (if they didn’t, your mixture didn’t have enough impurities or you didn’t mix enough Epsom salt into the liquid).
Pour off the extra water to examine your crystals. If you leave them in the liquid long, they will start to melt.
Our Epsom salt crystals started to melt about 5 minutes after we removed them from the refrigerator even though we did pour the extra liquid off. Perhaps we didn’t have quite enough Epsom salt in the mixture?
To make this more like a real experiment rather than a demonstration, you could try mixing several batches of salt with different quantities of salt, or try seeing if crystals form better in the refrigerator, freezer (but not long enough for the water to freeze), or at room temperature (which wouldn’t work, but kids would not know that).
