Chemistry is Fun not Magic

SILICA GARDEN

This is an interesting chemical experiment which beautifully

express the phenomenon of osmosis through semipermeable

membrane of silica gel. It looks a magic where colourful silica

grow in solution appear as colourful flowring garden The magic

solution in which garden grow is a solution of sodium silicate in

water. It is prepared by diluting water glass (concentrated

solution of sodium silicate available in market) five times with

distilled water. Salts used to make magic rocks which readily

available are:

Purple- Manganese chloride
Blue- Copper sulphate
Red- Cobalt chloride
Pink- Manganese chloride
Orange- iron chloride
Yellow- Iron chloride
Green - Nickel nitrate
White- Lead nitrate

The silica garden is prepared by placing crystals of various

coloured salts ( Apr. 0.4 mm size) in a magic solution of sodium

silicate prepared as above taken in a clean glass container .

In a few hours hollow tubes of metallic silicate gets shoot
up from these crystals which look like trees. If you add too

many crystals the solution will turn cloudy and immediate

precipitation will occur. A slower precipitation rate will give

you a nice garden. Once the garden grown , you can replace

the sodium silicate solution carefully with pure water. Initially

a colloidal and semipermeable shell of silicate is formed around

the crystal. Inside this is a strong solution of the salt and out side

is a weak solution of sodium silicate. Hence water permeates

into the shell and pressure rise until the shell bursts. At this

stage the salt solution escapes but immediately comes in the

contact with the sodium silicate solution and react with it to

form again semipermeable shell of the metallic silicate. Thus

the original condition is reproduced over and overagain and a

projection of silicate continusly grow.
The optimal concentration of magic solutio lie between

1.56 M and 0.625 m with respect to si9lica in experiment

where growth of silica tubes is vigorous. More concentated

solutionproduce meagre growth and thre is vigorous growth

from intermediate concentration while the more diluted

solution produces mearly a gelatinous mass. In more

concentrated solution the semipermeable membraneof

sodium silicate surrounding the seed crystal is broken

only with difficulty to produce the growth of tube. On the

other hand in dilute solution the membrane that is formed

acquire a more plassticcharacter and is not easily rupture

rather distords without breaking.