“Chemical garden” experiment
How to grow colorful seaweed from salts
In this experiment, you will learn how to turn a few pinches of salt into a chemical garden!
A similar experiment is included in the “Artificial sea” set from the MEL Chemistry subscription.
- Put on protective gloves and eyewear
- Conduct the experiment on the tray.
Reagents and equipment:
- sodium silicate solution (1 L);
- copper(II) sulfate pentahydrate (1 g);
- copper(II) chloride dihydrate (1 g);
- manganese(II) sulfate (1 g);
- cobalt (II) nitrate hexahydrate (1 g);
- iron(III) chloride, a small vessel (1 g).
Add a pinch of each salt to the sodium silicate solution: copper(II) sulfate pentahydrate, copper(II) chloride dihydrate, manganese(II) sulfate, cobalt (II) nitrate hexahydrate, and iron(III) chloride. Try to pour the salts in different areas of the cup so as to keep them from mixing. Watch as beautiful multicolored “seaweed” gradually grows from the salt crystals.
The sodium silicate solution can be prepared by combining ordinary silicate glue and water in a 1:1 ratio. When the metal salts are introduced to the solution, an exchange reaction begins, and a film of insoluble silicates forms around the salt crystals. This film is not 100% impermeable–it does allow water through.
The higher concentration of salt within the film than outside it causes a difference in osmotic pressure and draws water into the silicate shell. This causes the shell to widen and break. When this happens, the salts are again brought into contact with the silicate solution and a new silicate film forms. This process creates the chemical seaweed we observe. The seaweed’s color depends on its metal foundation: copper is light blue and green, manganese is pink, cobalt is dark blue, and iron is brown.