Chemical garden

Procedure

• Prepare a solution with 100 mL of commercial sodium silicate solution and 300 mL of water.
• Place sand at the bottom of the vial and add the sodium silicate solution.
• Let it settle for enough time for the sand to settle well and the liquid mixture not to be turbid.
• Slowly and one by one add the mineral salts. Observe what happens.

Theoretical explanation

This experiment consists of a metathesis reaction. After some minutes, the formation of different linear crystallizations will be observed, creating vertical structures resembling trees, made of metal silicates from the salts added. Due to the different colors of these silicates, the appearance is that of a small forest with multiple colors (white: Mn²⁺, violet: Co²⁺; green: Cu²⁺, Ni²⁺; ochre: Fe³⁺).

Metallic silicates are substances insoluble in water, and this causes when sodium silicate interacts with the various metallic cations from the salts, this precipitation in the form of an insoluble silicate membrane occurs. Water enters through the membranes of these insoluble silicates via osmosis, causing them to expand and eventually break, leading to the appearance of a new membrane and the repetition of the process.

Na₂SiO₃ + FeSO₄   FeSiO₃ + Na₂SO₄
Na₂SiO₃ + CuSO₄   CuSiO₃ + Na₂SO₄
Na₂SiO₃ + CoCl₂   CoSiO₃ + 2 NaCl
Na₂SiO₃ + NiSO₄   NiSiO₃ + Na₂SO₄
Na₂SiO₃ + MnSO₄   MnSiO₃ + Na₂SO₄
3 Na₂SiO₃ + 2FeCl₃   Fe₂(SiO₃)₃ + 6 NaCl

Did you know…? Silicates are abundant in the Earth’s crust and are present in numerous gemstones such as aquamarine, amethyst, garnet, or emerald.

Did you know…? Sodium silicate solution was used to preserve eggs. The shell was coated with this solution, and the pores were sealed so that the egg could last almost a year. More recently, it is used to prevent the attack of termites and as a fire retardant in old wood.