Chemical Garden
Encyclopedia
A chemical garden is an experiment in chemistry
normally done by adding solid
metal
salts such as copper sulfate or cobalt(II) chloride
to an aqueous solution of sodium silicate
(otherwise known as waterglass). This results in growth of plant like forms in minutes to hours. The chemical garden was first observed and described by Johann Rudolf Glauber
in 1646. In its original form, the chemical garden involved the introduction of ferrous chloride (FeCl2) crystals into a solution of potassium silicate
(K2SiO3).
Common salts used in a chemical garden
The chemical garden relies on the fact that most transition metal
silicates are insoluble in water and are coloured.
A metal salt such as cobalt chloride
will start to dissolve in the water. It will then form insoluble cobalt silicate by a double decomposition reaction (anion metathesis). This cobalt silicate is a semipermeable membrane
. Because the ionic strength
of the cobalt solution inside the membrane is higher than the sodium silicate solution which forms the bulk of the tank contents, osmotic effects will increase the pressure within the membrane. This will cause the membrane to tear, forming a hole. The cobalt cations will react with the silicate anions at this tear so forming new solid. In this way growths will form in the tanks; these will be coloured (according to the metal) and may look like plants. The crystal
s formed from this experiment will grow upwards, since the pressure at the bottom of the tank is higher than the pressure closer to the top of the tank, therefore forcing the crystals to grow upwards.
Note however that the upward direction of growth depends on the density of the fluid inside the semi-permeable membrane being lower than that of the surrounding waterglass solution. If one uses a very dense fluid inside the membrane, the growth is downward. For example, a fresh, green solution of trivalent chrome sulfate or chloride refuses to crystallise without slowly changing into the violet form, even if boiled till it concentrates into a tarry mass. That tar, if suspended in the waterglass solution, forms downward twig-like growths because all the fluid inside the membrane is too dense to float and thereby to exert upward pressure. The concentration of sodium silicate becomes important in growth rate. Although any concentration works, a ratio of 2ml of water to 3ml of sodium silicate works best.
While at first it might seem like the crystal garden is just a bit of fun, some serious work has been done on the subject. For instance this chemistry is related to the setting of cement
, and during the corrosion
of steel surfaces tubes can be formed. A chemical garden helps one to understand the nature of that chemical substance.
The nature of the growth also is useful in understanding classes of related behaviour seen in fluids separated by membranes. In various ways it resembles the growth of spikes or blobs of ice extruded above the freezing surface of still water, the patterns of growth of gum drying as it drips from wounds in trees such as Eucalyptus
spp. and the way molten wax forms twig-like growths, either dripping from a candle, or floating up through cool water.
The resulting garden should not be shaken, since the plants are very delicate in nature. After the growth has ceased sodium silicate solution can be removed by continuous addition of water at a very slow rate. This will prolong the life of garden.
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
normally done by adding solid
Solid
Solid is one of the three classical states of matter . It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a...
metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
salts such as copper sulfate or cobalt(II) chloride
Cobalt(II) chloride
Cobalt chloride is an inorganic compound of cobalt and chloride, with the formula CoCl2. It is usually supplied as the hexahydrate CoCl2·6H2O, which is one of the most commonly used cobalt compounds in the laboratory. The hexahydrate is deep purple in color, whereas the anhydrous form is sky blue...
to an aqueous solution of sodium silicate
Sodium silicate
Sodium silicate is the common name for a compound sodium metasilicate, Na2SiO3, also known as water glass or liquid glass. It is available in aqueous solution and in solid form and is used in cements, passive fire protection, refractories, textile and lumber processing, and automobiles...
(otherwise known as waterglass). This results in growth of plant like forms in minutes to hours. The chemical garden was first observed and described by Johann Rudolf Glauber
Johann Rudolf Glauber
Johann Rudolf Glauber was a German-Dutch alchemist and chemist. Some historians of science have described him as one of the first chemical engineers...
in 1646. In its original form, the chemical garden involved the introduction of ferrous chloride (FeCl2) crystals into a solution of potassium silicate
Potassium silicate
Potassium silicate is a water-soluble and glass-forming silicate salt of general formula K2SiO3 with many common uses for at least a century.-Woodwork protection against fire:...
(K2SiO3).
Common salts used in a chemical garden
- Aluminium potassium sulphateAlumAlum is both a specific chemical compound and a class of chemical compounds. The specific compound is the hydrated potassium aluminium sulfate with the formula KAl2.12H2O. The wider class of compounds known as alums have the related empirical formula, AB2.12H2O.-Chemical properties:Alums are...
crystals - (White) - Copper(II) sulphate crystals - (Blue)
- Chromium(III) chlorideChromium(III) chlorideChromium chloride is a violet coloured solid with the formula CrCl3. The most common form of CrCl3 sold commercially is a dark green hexahydrate with the formula [CrCl24]Cl.2H2O. Two other hydrates are known, pale green [CrCl5]Cl2.H2O and violet [Cr6]Cl3...
crystals - (Green) - Nickel(II) sulphate crystals - (Green)
- Iron(II) sulphate crystals - (Green)
- Iron(III) chlorideIron(III) chlorideIron chloride, also called ferric chloride, is an industrial scale commodity chemical compound, with the formula FeCl3. The colour of iron chloride crystals depends on the viewing angle: by reflected light the crystals appear dark green, but by transmitted light they appear purple-red...
crystals - (Orange) - Cobalt(II) chlorideCobalt(II) chlorideCobalt chloride is an inorganic compound of cobalt and chloride, with the formula CoCl2. It is usually supplied as the hexahydrate CoCl2·6H2O, which is one of the most commonly used cobalt compounds in the laboratory. The hexahydrate is deep purple in color, whereas the anhydrous form is sky blue...
crystals - (Purple)
The chemical garden relies on the fact that most transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...
silicates are insoluble in water and are coloured.
A metal salt such as cobalt chloride
Cobalt(II) chloride
Cobalt chloride is an inorganic compound of cobalt and chloride, with the formula CoCl2. It is usually supplied as the hexahydrate CoCl2·6H2O, which is one of the most commonly used cobalt compounds in the laboratory. The hexahydrate is deep purple in color, whereas the anhydrous form is sky blue...
will start to dissolve in the water. It will then form insoluble cobalt silicate by a double decomposition reaction (anion metathesis). This cobalt silicate is a semipermeable membrane
Membrane (selective barrier)
A membrane is a layer of material which serves as a selective barrier between two phases and remains impermeable to specific particles, molecules, or substances when exposed to the action of a driving force...
. Because the ionic strength
Ionic strength
The ionic strength of a solution is a measure of the concentration of ions in that solution. Ionic compounds, when dissolved in water, dissociate into ions. The total electrolyte concentration in solution will affect important properties such as the dissociation or the solubility of different salts...
of the cobalt solution inside the membrane is higher than the sodium silicate solution which forms the bulk of the tank contents, osmotic effects will increase the pressure within the membrane. This will cause the membrane to tear, forming a hole. The cobalt cations will react with the silicate anions at this tear so forming new solid. In this way growths will form in the tanks; these will be coloured (according to the metal) and may look like plants. The crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
s formed from this experiment will grow upwards, since the pressure at the bottom of the tank is higher than the pressure closer to the top of the tank, therefore forcing the crystals to grow upwards.
Note however that the upward direction of growth depends on the density of the fluid inside the semi-permeable membrane being lower than that of the surrounding waterglass solution. If one uses a very dense fluid inside the membrane, the growth is downward. For example, a fresh, green solution of trivalent chrome sulfate or chloride refuses to crystallise without slowly changing into the violet form, even if boiled till it concentrates into a tarry mass. That tar, if suspended in the waterglass solution, forms downward twig-like growths because all the fluid inside the membrane is too dense to float and thereby to exert upward pressure. The concentration of sodium silicate becomes important in growth rate. Although any concentration works, a ratio of 2ml of water to 3ml of sodium silicate works best.
While at first it might seem like the crystal garden is just a bit of fun, some serious work has been done on the subject. For instance this chemistry is related to the setting of cement
Cement
In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...
, and during the corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
of steel surfaces tubes can be formed. A chemical garden helps one to understand the nature of that chemical substance.
The nature of the growth also is useful in understanding classes of related behaviour seen in fluids separated by membranes. In various ways it resembles the growth of spikes or blobs of ice extruded above the freezing surface of still water, the patterns of growth of gum drying as it drips from wounds in trees such as Eucalyptus
Eucalyptus
Eucalyptus is a diverse genus of flowering trees in the myrtle family, Myrtaceae. Members of the genus dominate the tree flora of Australia...
spp. and the way molten wax forms twig-like growths, either dripping from a candle, or floating up through cool water.
The resulting garden should not be shaken, since the plants are very delicate in nature. After the growth has ceased sodium silicate solution can be removed by continuous addition of water at a very slow rate. This will prolong the life of garden.
External links
- Chemical gardens in space: Link
See also
- The toy based on chemical gardens: Magic rocksMagic rocksMagic Rocks, also sometimes referred to or marketed as Crystal Gardens or Chemical Gardens, are a novelty item for creating rock-like formations. A typical package of Magic Rocks contains an envelope of liquid sodium silicate and a small handful of colored "rocks" that are actually chunks of water...
- Simple classroom demonstrations: Mercury beating heartMercury beating heartThe mercury beating heart is an electrochemical redox reaction between the elements mercury, iron and chromium. The reaction causes a blob of mercury in water to oscillate....
- Barking dog reactionBarking dog reactionThe "Barking Dog" is an exothermic chemical reaction that results from the ignition of a mixture of carbon disulfide and nitric oxide .It has been known for centuries; in 1853, Justus von Liebig was using the bright blue flash and the distinctive ‘woof’ sound of the demonstration to enthrall his...