Chemical Garden, deeper conceptual explanation

  • Thread starter mishima
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mishima
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Hey there, I am curious why certain metal salts grow faster in a chemical garden. As I understand, the growth is more of a physical process than a chemical one. The difference in density causes the metal silicate to rise in solution, and osmotic processes inflate the tubes.

However, at least initially, I suspect how quickly the metal salt dissolves in the sodium silicate is proportional to how quickly the tubes grow.

I have observed for example that cobalt (II) chloride hexahydrate grows faster than iron (II) sulfate heptahydrate. What could be the theoretical explanation for the difference in growth rate for these two substances?

There is not a lot of information on the actual process behind these gardens online. Thanks.
 
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  • #2
Just a personal opinion: probably the most important factor is the speed of water transport through the silicate membrane.
 
  • #3
How would the type of metal affect this rate? Could it be proportional to the bond strength between the metal cation and the silicate? In other words a tighter lattice would slow the rate?
 
  • #4
mishima said:
In other words a tighter lattice would slow the rate?

Yes, that's what I would expect, although I have no idea how to precisely quantify the "tightness". Different silicates can probably take different forms, arrangement of atoms in the membrane is probably to some extent ordered (as in crystals) and to some extent anisotropic, depending on the scale. These membranes are highly hydrated, so their properties are quite different from the crystalline silicates of respective metals.

Definitely mechanical strength and permeability of different membranes will vary, some combination of these will be responsible for how easily the membrane breaks and how fast the "branches" grow.
 

What is a chemical garden and how is it formed?

A chemical garden is a fascinating scientific phenomenon where various metal salts are added to a solution of sodium silicate (water glass), resulting in the growth of colorful, plant-like structures. These structures form as the metal salts react with the silicate in the solution, creating insoluble metal silicates that precipitate out. This precipitation happens in a way that allows the structures to rise, resembling plant stalks, due to the less dense silicate "membranes" forming around the metal salt solutions that are being pushed upwards by osmotic pressure.

What role does osmotic pressure play in the formation of a chemical garden?

Osmotic pressure is crucial in the development of a chemical garden. When the metal salt pellets are introduced to the sodium silicate solution, each pellet starts to dissolve, forming a concentrated solution. This solution has a higher osmotic pressure compared to the surrounding less concentrated silicate solution, leading to the flow of water into the concentrated regions. This influx increases the internal pressure, causing the gel-like silicate to form a semi-permeable membrane, through which more water continues to flow, pushing the newly formed silicate structures upward, thus contributing to the "growth" of the garden.

What types of chemical reactions occur in a chemical garden?

In a chemical garden, the primary reactions involve the precipitation of metal silicates. When metal salts like copper sulfate, iron chloride, or cobalt nitrate are added to sodium silicate, the metal ions react with the silicate ions to form insoluble metal silicates. This results in the colorful, solid structures characteristic of a chemical garden. Additionally, secondary reactions might occur depending on the specific metal salts used, which can influence the color and shape of the precipitates.

Why do different metal salts produce different colors in a chemical garden?

The different colors produced in a chemical garden are due to the specific metal ions present in the salts used. Each metal ion has a characteristic color when it forms a compound with silicate. For example, copper typically forms blue or green precipitates, cobalt forms pink or blue, while iron might result in rusty brown or green. These colors are the result of how these metal silicate compounds absorb and reflect specific wavelengths of light, which is intrinsic to the electronic structure of the metal ions.

Can the growth patterns of a chemical garden be controlled or influenced?

The growth patterns in a chemical garden can be influenced by several factors including the concentration of the sodium silicate solution, the type and concentration of the metal salts used, and the temperature of the solution. Adjusting these parameters can affect the rate of reaction and the solubility of the precipitates, thereby influencing the size, shape, and texture of the growing structures. Additionally, the placement of metal salt pellets in the solution can determine the initial sites of growth, allowing some control over the structure's development.

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