Solutions
13.1 Celery or Carrot in Salt Solution vs Distilled Water
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Subjects:Solutions, osmosis
Description: A piece of celery (or carrot, potato, etc) is placed in a salt solution. The piece of celery or carrot will shrivel. Conversely, when celery is placed in a deionized water solution, it will swell.
Materials:
- 2 Celery pieces (or carrot or potato) #
- 1M sodium chloride solution‡
- Water
- 2 400 mL beakers
#Advanced preparation: vegetable must be supplied by instructor.
‡Located on general chemistry solutions shelf.
Procedure:
1. Pour the salt solution in one beaker and DI water into the other.
2. Place one piece of vegetable in the salt solution and another in the distilled water and observe.
Discussion:
Osmosis is a process in which solvent molecules flow through a semipermeable membrane. This membrane allows the passage of the solvent, but not the solutes.
Water flows from the region of low solute concentration (hypotonic) to high solute concentration (hypertonic). The movement of solvent through a membrane produces a pressure called the osmotic pressure. The movement of the solvent through the membrane will continue until an equilibrium is met. This happens when the pressure in the compartment into which the solvent is flowing is raised to the equivalent of the pressure of the solvent moving through the membrane from the hypotonic side (osmotic pressure).
Osmosis is a colligative property in that it depends on the concentrations of the solutes, but not the identity of the solutes.
The cells of plants contain an aqueous solution of salts, proteins and enzymes. Compared to distilled water, the solution within the cell walls is hypertonic. Therefore when celery is placed in water, the water flows into the cells of the celery. This can be used to refresh limp celery. As the pressure of the water in the cells increases, the crispness of the celery increases.
A saltwater solution is hypertonic compared to the aqueous solution inside the cells. Therefore when the celery is placed in the saltwater solution water flows out of the celery, causing it to shrivel.
References:
1. B. Z. Shakhashiri; Chemical Demonstrations: A Handbook for Teachers of Chemistry; Wisconsin; Volume 3; 1989; p. 283-285
2. J. Kotz, P. Treichel, J. Townsend; Chemistry & Chemical Reactivity; 7th Ed; Teachers Edition; Brooks/Cole; 2009; p. 635-637
