“Bloody red crystals” experiment
How to grow different crystals from one substance
Secret treasures are always associated with distant journeys. But you can also acquire jewels by a more economical method: for example, the red “twin” of the ruby can be obtained in the laboratory!
Wear protective gloves and glasses.
Reagents and equipment:
- potassium hexacyanoferrate(III) (480 g);
- hot water (800 ml);
- fishing line;
- cotton wool.
Sprinkle potassium hexacyanoferrate(III) into the cup and pour hot water over it. Stir thoroughly for 10–15 minutes. We get a saturated solution. Separate the solution from the remaining crystals and dust using a funnel with cotton wool. Cover the solution with foil and leave in a dark place. 24 hours later, pour the solution into another cup. Place the crystals that have formed in a sealed container, so they do not disintegrate. Lower seeds for crystals into the saturated solution of potassium hexacyanoferrate (III):
- attach cotton wool to the fishing line, soak it in the saturated solution of potassium hexacyanoferrate(III) and dry;
- from the crystals obtained earlier, select the crystal with the most regular shape and attach it to the fishing line;
- simply let the third seed–the small crystal–sink to the bottom.
Unlike precious stones, crystals of potassium hexacyanoferrate(III) are soluble in water. So if you don’t like the shape of the crystal, the experiment can easily be repeated.
In a saturated solution, a substance is at maximum concentration and does not dissolve further at the given temperature. At room temperature (25 °С, 77 °F), the solubility of potassium hexacyanoferrate(III) in water is around 50 g/100g of water. When heated to 90 °С (194 °F), solubility increases to 92–100 g of water. When the hot solution cools down, it becomes oversaturated, i.e. more of the substance is dissolved in it at the given temperature. As a result, the “surplus substance”–in our case potassium hexacyanoferrate(III)–precipitates in the form of crystals, and the solution becomes saturated once more. This is how the seeds for the crystals were formed.
A saturated solution from which water evaporates becomes oversaturated. As a result, the surplus of salt precipitates, and the crystals grow from it. If seeds are placed in this solution, for example, a crystal or cotton wool with crystals, they do not dissolve, but will become covered in ions of the dissolved salt, thus forming crystals of a large size.