How do you dissolve cellulose
5.1.1 Dissolving cellulose in s reagent
Material / chemicals:
- Cotton wool
- Cu (OH)2(harmful to health)
- NH3 conc. (25%) (corrosive)
- least. water
- 2 beakers (400 ml)
Execution of the experiment:
- 3 g of cotton wool are placed in 100 ml of water
- 2 g Cu (OH)2 are dissolved in 105 mL ammonia. The result is a deep blue solution that s reagent.
3 g of cotton wool are added to Schweizer's reagent and the mixture is stirred until the cellulose has dissolved.
|A. The cellulose shows no visible change.|
|B. The cellulose dissolves. A deep blue, clear solution is created.|
- The cellulose is insoluble in water because the cellulose chains are strongly connected by hydrogen bridges.
The long cellulose chains combine to form crystal-like structures that water cannot dissolve. The water molecules penetrate between the cellulose chains - the cellulose swells - but do not bring them into solution.
- In Schweizer's reagent, the cellulose dissolves as a copper-cellulose complex. The Cu present in the solution2+-Ions with ammonia initially form the deep blue colored copper tetrammine complex [Cu (NH3)4]2+. At a high pH value, this reacts with the cellulose and breaks the hydrogen bonds between the cellulose chains.
The crystal-like structures are broken down and water molecules can loosen the complexed cellulose chains.
The copper cellulose solution and its residues are disposed of in the heavy metal waste.
- All devices that have come into contact with the copper cellulose solution are cleaned with diluted ammonia before rinsing with water, as otherwise insoluble cellulose residues can form.
- The experiment should be carried out near the table fume cupboard, as the ammonia odor that arises can be very unpleasant.
You can watch the demo video here:
5.2.2 Production of a regenerated cellulose film using the copper silk process
© 2001Markus Förg, [email protected]
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