Chemistry Project

2013Chemistry ProjectChemical GardenKoustav Pal

Chemical GardenIntroduction: The chemical garden is a fascinating phenomenon which was first observed by Johann Rudolf Glauber a scientist that historians have accredited with being one of the first chemical engineers. In 1646, Johann had observed the effect of FeCl2 Crystals in a solution of K2SiO3. Upon adding the crystals to this solution, he observed the growth of a tall, plant like precipitate which grew within a few hours.Materials: 40g Sodium Hydroxide Pellets 60g Silica Gel 500 ml of Distilled Water Bunsen Burner Tripod Gauze Glass Rod A variety of Transition Metal Salts 600ml Beaker A funnel Measuring Cylinder Filter Paper

Method: 1. A solution of NaOH is prepared by adding 40g of NaOH to 100ml of Distilled water. The glass rod is used to stir and dissolve the NaOH to form the solution. 2. The Bunsen burner is setup with the tripod. The beaker is placed on top of the gauze and is allowed to heat the beaker. Small amounts of silica gel are added and stirred into the solution between cooling periods, eventually dissolving all 60g of the silica into the solution.3. The solution is removed from the Bunsen burner, and is now allowed to cool. Once cooled, it is diluted to 250ml and then is filtered to obtain a pure solution lacking in impurities. 4. The clear solution is finally diluted to 550ml within a 600ml beaker. 5. Small pellets of transition salts are added to the solution, one at a time, but not in excess.6. The mixture is now allowed to sit in an undisturbed location to form the precipitates.

Observation:

Within two to three hours of adding the pellets, a fibrous colored tower forms depending on the salt pellet added. This tower is approximately is as tall as the distance from the bottom of the beaker to the surface of the sodium silicate solution.

Name of CrystalColor Observed

Cobalt (II) ChloridePurple

Copper (II) SulphateBlue

Iron (III) ChlorideOrange

Nickel (II) SulphateGreen

AlumWhite

Explanation of the phenomenon:

Adding a pellet of a soluble metal salt to the water glass solution initiates a morphogenic reaction where a hydrous metal silicate gel forms around the crystal, due to anion metathesis. The formation of this colloidal gel acts as a semi-permeable membrane through which water and excess hydroxide ions enter due to the osmotic pressure. Under the entering water and hydroxide ions the crystal begins to dissolve. As a result the dissolved crystal causes the gel to stretch until it ruptures, forming a small tear through which a jet of the dissolved fluid is ejected. At these points of ejection, a tubular fiber forms, and this process repeats, forming a large tower in due time. Thus, this phenomenon follows Hoffs law of osmotic pressure.

Practical uses of the Chemical Garden: Currently the principles of this experiment are used to as a mechanism for the setting of Portland Cement. Solid Calcium Silicates are immersed in water; a membrane of calcium silicate hydrate is forms around the calcium silicate. Following this, osmotic pressure draws in hydroxide and water into the membrane, eventually rupturing the membrane to eject several tubular filaments of the calcium silicate hydrate. As a result cement consists of a thick intermesh of these filaments. It can be used to understand the corrosion of metals which maybe colloidal in character. In Lead Acid battery technology, a battery paste which is colloidal in nature, following this membrane osmosis model can be implemented to function.

Works Cited"Chemical Garden." Wikipedia. N.p.: n.p., n.d. N. pag. Print.Collins, Craig. "The Silica Garden: A Hierarcharical Nanostructure." Chemical Physics Letters: n. pag. Print.