Weird Science

Chemical Garden

Polish ver­sion is here

Diving into Lite­ra­ture!

Lite­rary fic­tion and the exact scien­ces do not always have to be worlds apart; some­ti­mes, they find com­mon gro­und. Tho­mas Mann, one of the gre­a­test Ger­man wri­ters, descri­bed a fasci­na­ting expe­ri­ment in his novel:

I shall never for­get the sight. The ves­sel of cry­stal­li­za­tion was thre­e­qu­ar­ters full of sli­gh­tly muddy water — that is, dilute water-glass — and from the sandy bot­tom there strove upwards a gro­te­sque lit­tle land­scape of vario­u­sly colo­u­red grow­ths: a con­fu­sed vege­ta­tion of blue, green, and brown sho­ots which remin­ded one of algae, mush­ro­oms, atta­ched polyps, also moss, then mus­sels, fruit pods, lit­tle trees or twigs from trees, here and there of limbs. It was the most remar­ka­ble sight I ever saw, and remar­ka­ble not so much for its appe­a­rance, strange and ama­zing tho­ugh that was, as on acco­unt of its pro­fo­un­dly melan­choly nature. For when Father Lever­kiihn asked us what we tho­u­ght of it and we timi­dly answe­red him that they might be plants: “No,” he replied, “they are not, they only act that way. But do not think the less of them. Pre­ci­sely because they do, because they try to as hard as they can, they arc wor­thy of all respect.”

Tho­mas Mann: Doc­tor Fau­stus, trans. H. T. Lowe-Por­ter

This expe­ri­ment is aptly named the "che­mi­cal gar­den," and it can easily be con­duc­ted by any che­mi­stry enthu­siast. Howe­ver, before we pro­ceed with the prac­ti­cal work, we need to under­stand some fun­da­men­tal the­o­re­ti­cal con­cepts.

A lit­tle bit of the­ory

The for­ma­tion of struc­tu­res resem­bling plant life is lar­gely gover­ned by osmo­sis. Osmo­sis refers to the move­ment of a solvent thro­ugh a semi­per­me­a­ble mem­brane that sepa­ra­tes two solu­tions of dif­fe­rent con­cen­tra­tions. A semi­per­me­a­ble mem­brane is a bar­rier that allows the pas­sage of solvent mole­cu­les while restric­ting dis­so­lved sub­stan­ces. Osmo­sis natu­rally occurs from a solu­tion with a lower solute con­cen­tra­tion to one with a higher con­cen­tra­tion, aiming to equ­a­lize the solute levels, as illu­stra­ted in the dia­gram below:

Ilustracja

Bio­lo­gi­cal mem­bra­nes also act as semi­per­me­a­ble bar­riers, play­ing a cru­cial role in the struc­ture and func­tion of living orga­ni­sms.

Such semi­per­me­a­ble bar­riers can also form under spe­ci­fic con­di­tions during the reac­tion between sodium sili­cate and cer­tain metal salts. These reac­tions are pre­ci­sely what ena­ble the cre­a­tion of the che­mi­cal gar­den.

Requ­i­red Mate­rials

We will need the fol­lo­wing:

The expe­ri­ment requ­i­res sodium sili­cate and at least one of the listed metal salts. Howe­ver, using mul­ti­ple salts will pro­duce a more visu­ally cap­ti­va­ting spec­trum of colors. The con­cen­tra­tion of sodium sili­cate sho­uld be deter­mi­ned expe­ri­men­tally. Here are the neces­sary rea­gents:

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War­ning: Tech­ni­cal grade water glass con­ta­ins NaOH, a strong base with cor­ro­sive pro­per­ties. Avoid con­tact with skin and eyes at all costs! Addi­tio­nally, some of the metal salts used in this expe­ri­ment are highly toxic and/or car­ci­no­ge­nic. Pro­tec­tive glo­ves must be worn at all times, and skin con­ta­mi­na­tion sho­uld be stric­tly avo­i­ded. The author takes no respon­si­bi­lity for any poten­tial har­m—pro­ceed at your own risk!

To begin, sprin­kle a few cry­stals of the selec­ted metal salts at the bot­tom of a bea­ker, then care­fully pour in the sodium sili­cate solu­tion. Almost imme­dia­tely, the cry­stals will begin to "ger­mi­nate," for­ming color­ful, bran­ching struc­tu­res. These grow­ths deve­lop at a rate visi­ble to the naked eye. Within minu­tes, the bea­ker will be fil­led with twi­sting, mul­ti­co­lo­red for­ma­tions that clo­sely resem­ble actual plants. Below are some ima­ges of these pseudo-plants for­med in my lab:

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Ilustracja:

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The pro­cess of their growth is truly mesme­ri­zing and visu­ally stun­ning:

Expla­na­tion

What cau­ses the for­ma­tion of these fan­ta­sti­cal struc­tu­res? When the metal salt cry­stals come into con­tact with the sodium sili­cate solu­tion, a che­mi­cal reac­tion occurs, resul­ting in the for­ma­tion of metal sili­ca­tes. These sili­ca­tes are only sli­gh­tly solu­ble in water, so they pre­ci­pi­tate out as a thin mem­brane sur­ro­un­ding the cry­stal. Here, osmo­sis comes into play: since the inte­rior of the mem­brane con­ta­ins a higher con­cen­tra­tion of salts, water begins to dif­fuse inward, incre­a­sing inter­nal pres­sure. As the pres­sure builds, the mem­brane stret­ches until it even­tu­ally rup­tu­res. Thro­ugh this rup­ture, some of the salt solu­tion esca­pes and reacts with the sodium sili­cate, for­ming a new mem­brane. This pro­cess repe­ats con­ti­nu­o­u­sly, gene­ra­ting the intri­cate, plant-like struc­tu­res. The color of the "plants" depends on the spe­ci­fic metal sili­cate for­med.

Enjoy! :)

Fur­ther rea­dings:

Marek Ples

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