Diffusion and Osmosis

Lab 4

Objectives:1.- Be able to define the following terms in writing: a- solution f- differentially permeable memb. b- solute g- osmosis c- solvent h- net movement d- relative concentration e- diffusion2.- Be able to explain why a particular material diffuses

in a particular direction.3.- Be able to determine the net direction of diffusion.4.- Be able to differentiate between diffusion and

osmosis.5.- Be able to describe the influence of temperature on

the rate of osmosis.

• The molecular theory states that all substances are made up of molecules that occupy space and are constantly in motion.

• This exercise will help you examine some phenomena related to this motion of molecules

During this lab excercise you can:

• 1.- Observe the diffusion of a gaseous material through air (ammonia)

• 2.- Set up a demonstration of osmosis under a variety of temperature conditions to determine how these temperatures influence the rate of osmosis

• 3.- Graph the results of the osmosis demonstrations

Experiments• Diffusion of Ammonia• Diffusion of Sugar• Diffusion of Chloride ions (semi-permeable

membrane) In each of the previous examples, the net

movement was a result of diffusion of molecules diffusion of molecules from a place of higher concentration to a place from a place of higher concentration to a place of lower concentration.of lower concentration. The rate at which diffusion occurs is related to the amount of energy the molecules contain. Adding energy does not cause relative concentration, nor does it influence direction of diffusion; it merely affects the rate at which diffusion occurs.

Osmosis Osmosis is a specific type of diffusion; it is the is a specific type of diffusion; it is the

movement of water through a semi-permeable movement of water through a semi-permeable membranemembrane..

In any type of osmosis we are concerned with the relative concentration of water molecule on either side of the membrane, which is permeable to water. When water intermingles with other molecules, it is called a solutionsolution..

• Water is the solvent and the dissolved substance the dissolved substance is the soluteis the solute.. A solution is characterized by the solute; for example, water and glucose would be characterized by solute; for example, water and glucose would be characterized as a glucose solution.

Effect of Membrane Permeability on Diffusion and Osmosis

Figure 3.8a

Osmosis experiment• Working in pairs, prepare a model to

demonstrate osmosis.

• Obtain a piece of dialysis tubing (sausage casing) and soak it in tap water for about one minute.

• Shake off the surplus water and, with a piece of string, securely tie one end so that you for tubular bag that is leak proof at that end.

• Fill the tubular bag with glucose solution

• The bag should be so full that glucose will overflow.

• With a second piece of string, tie the open end and rinse the excess glucose from the outside of the bag.

• Notice the appearance of the bag and weigh the bag. Place the glucose bag into a beaker containing enough tap water to completely cover the bag. After five minutes, remove the bag and weigh it again. Note the size, shape, and firmness of the bag.