“Copper sulfate crystals” experiment
How to grow a beautiful blue crystal with a copper salt
We all like stories about heroes who go on endless quests to find treasure. But sometimes treasures can be found very nearby. In this experiment, we’ll show you how to grow a beautiful blue crystal, without traveling to the ends of the Earth.
Wear protective gloves and glasses.
Warning! Only under adults supervision.
Reagents and equipment:
- copper(II) sulfate pentahydrate (70 g);
- hot water (100 ml);
- plastic twine;
- funnel with cotton wool;
Sprinkle copper(II) sulfate pentahydrate into a beaker and pour hot water over it. Stir thoroughly for 10-15 minutes. In this way, we make a saturated solution. Remove the remaining crystals and dust from the solution using the funnel with cotton wool. Cover the solution with foil and leave in a dark place for 24 hours.
Then pour the solution into another beaker and take out the crystals that have formed. It’s important to choose a crystal with the right form, without cracks and other defects. Tie twine around the crystal and immerse it in the solution we made previously, so that the crystal does not touch the walls of the beaker. Cover with foil and put in a dark place. After a month a large crystal will grow on the twine!
In a saturated solution, the substance is at maximum concentration and does not dissolve further at the given temperature. At room temperature (25 °С, 77 °F), the solubility of copper(II) sulfate pentahydrate in water is around 35 g/100 g of water. When heated to 90 °С (194 °F), solubility increase to 100 g/100 g of water.
So when it cools the solution becomes saturated, i.e. more of the substance is dissolved in it at the given temperature. As a result, the “surplus substance”–copper(II) sulfate pentahydrate in our case – precipitates in the form of crystals, and the solution once more becomes saturated. If you place a crystal in this solution, it will not dissolve, but become covered with ions of the dissolved salt.