SC 2014 Semilab: Diffusion and Osmosis

by Oxana Litvin

When a thirsty stranger arrives to an oasis after a long march through Sahara desert, the locals warn him not to drink too much water. When fishers want to preserve fish they caught they add plenty of salt to it. When you fill one balloon with helium, and another balloon with air, the first one quickly loses its shape and size, whereas the second remains inflated. Is there anything in common between these phenomenae? Apparently, yes: diffusion and osmosis.

In this introductory level semilab we will explore principles and real life applications of diffusion and osmosis. Diffusion is movement of particles from area of high concentration to area of low concentration, and osmosis is particular case of diffusion, when particles of water are moving through thin films with microscopic pores. It is amazing that such a simple phenomenon is basis of ancient method of food preservation by salt, cleaning of blood of waste materials in kidneys, and ability of plants to absorb water from soil. In this lab we will explore diffusion of gases and particles in solutions, learn how to measure a rate of diffusion, and what is the effect of temperature and size of particles on diffusion rate. We will deal with diffusion of odors and food coloring, acids and bases, chemical reactions between them and color indicators which used to detect acidity, osmosis in plant and animal tissues, and dialysis in semi-permeable membrane.

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