Osmose

Introduction à l'osmose : mouvement des molécules à travers une membrane semi-perméable sous l'effet d'un gradient de concentration, qui constitue le principe de base de l'absorption d'eau.

Ce que les élèves apprennent

Les fondements scientifiques de cette expérience

Matériel utilisé

Produits chimiques et réactifs

Consignes de sécurité

Questions destinées aux élèves

À quoi s'attendre

<p>The level of liquid inside the tube rises to a determined height and will then stop.</p><p>Osmotic pressure is a result of the natural tendency of solutions of different concentrations to mix to a uniform concentration.</p><p>If two solutions are separated by a semipermeable membrane the system tends to reach a constant concentration. Water molecules exert a pressure on the membrane and on the solution at lower concentration.</p><p>The essence of an osmosis experiment is a membrane separating solutions of differing concentrations. This membrane must be selectively permeable, that is, it must be permeable to the solvent but impermeable to the solute.</p><p>Thus the sodium chloride remains within the thistle tube but water is free to pass in either direction. A high concentration solution will always move to a more concentrated solution.</p><p>The membrane you are using is taken from dialysis tubing that blocks the passage of molecules whose molecular weight exceeds 10,000 amu. At a mere 18 amu, water has no difficulty with such a membrane, but macromolecules such as proteins can have molecular weights that easily exceed this value. (1000 amu = 1 kiloDalton or kD.).</p><p>The apparatus is built so that as the water diffuses into it, the solution is forced up the tube against gravity. Since the solute always stays within the tube, it can never reach the zero concentration of the pure water solution on the other side of the membrane. The solution will not rise indefinitely.</p><p>The "free energy of mixing" is countered by the gravitational energy associated with the solution's rise until the two solutions establish equilibrium. If the solutions are ideal (or nearly so) the pressure is given by the osmotic pressure expression. The measured pressure, in mm Hg, is the mm of solution scaled by the ratio of the densities of the solution and mercury. The density of Hg = 13.6 g/cc.</p><p> = (n / V) RT = C RT.</p>

Élimination

Jetez les liquides dans le conteneur destiné aux déchets d'acides et de bases.

Réalisez cette expérience dans votre classe

Cette expérience fait partie d'ATP « Mobile Lab » — un laboratoire autonome qui transforme une salle de classe ordinaire en véritable laboratoire scientifique, proposant plus de 200 expériences en physique, chimie, biologie, robotique et ingénierie. « Gali », le tuteur basé sur l'IA intégré à ATP Connect, guide les élèves à chaque étape et répond à leurs questions pendant les travaux pratiques.