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- diffusion
2.- 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
from a place of higher concentration to a place
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
movement of water through a semi-permeable
membrane.
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 solution.
• Water is the solvent and the dissolved substance
is 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.