"Traube Cell" experiment

Bi­ol­o­gy and chem­istry are close­ly con­nect­ed, and in this en­light­en­ing ex­per­i­ment we will learn to cre­ate ar­ti­fi­cial cells by a chem­i­cal re­ac­tion.

Reagents and equip­ment:

• 5% cop­per sul­fate so­lu­tion;
• potas­si­um fer­ro­cyanide tablets;
• dis­tilled wa­ter;
• beaker;
• cu­vette;
• tongs

Step-by-step in­struc­tions

Dis­solve 50 g of cop­per sul­fate in 950 g of dis­tilled wa­ter. Pour the so­lu­tion into the cu­vette. Add sev­er­al tablets of potas­si­um fer­ro­cyanide.

Pro­cess­es de­scrip­tion

Semi-per­me­abil­i­ty is the abil­i­ty to pass cer­tain sub­stances through a mem­brane se­lec­tive­ly. Mem­branes of plant cells have this prop­er­ty, for ex­am­ple. In the in­ter­ac­tion of potas­si­um fer­ro­cyanide with cop­per sul­fate, cop­per hex­a­cyano­fer­rate (II) forms, which has prop­er­ties of semi-per­me­abil­i­ty. This was es­tab­lished by the Ger­man physi­cist and phys­i­ol­o­gist Moritz Traube. His work showed that it was pos­si­ble to find chem­i­cal com­pounds which on in­ter­ac­tion be­came com­plete­ly sim­i­lar to a plant cell,ca­pa­ble of tak­ing some sub­stances from the en­vi­ron­ment and se­cret­ing oth­ers:

2Cu­SO₄ + K₄[Fe(CN)₆] → Cu₂[Fe(CN)₆] + 2K₂­SO₄

The con­cen­tra­tion of potas­si­um fer­ro­cyanate in­side the cell is greater than the con­cen­tra­tion of cop­per sul­fate out­side it, and so wa­ter starts to en­ter the cell, thus ex­pand­ing it un­til the con­cen­tra­tions of potas­si­um fer­ro­cyanate and cop­per sul­fate be­come equal. The growth of the Traube cell takes place un­even­ly, as the mem­brane of cop­per hex­a­cyano­fer­rate (II) grad­u­al­ly breaks from pres­sure, and in the place of the break the cop­per sul­fate and potas­si­um fer­ro­cyanate in­ter­act once more, and a film forms again.

Safe­ty pre­cau­tions

Wear pro­tec­tive gloves and glass­es dur­ing the ex­per­i­ment.

Warn­ing! Only un­der pro­fes­sion­al su­per­vi­sion.