Liquid Density Demonstration
Name: Dan B.
Date: Saturday, November 16, 2002
Yellowish Corn oil for cooking floats nicely on White
vinegar with a drop of food coloring. This is an easy and cheap 2 layer
liquid density demonstration. Three layers would be much more
impressive. What is a relatively cheap and easy to get liquid that is
insoluble in vinegar AND Oil?
Use corn oil, dyed water, and then drop a few mothballs into the system.
Insoluble in either corn oil or water, they'll sink to the bottom because
their density is greater than that of the oil or water. Mothballs are made
of naphthalene. Moth crystals are para-dichlorobenzene. Use mothballs.
HOW ABOUT 4, 5,OR 6 LAYERS??
This makes a great science demo. You can even make it a class competition to
see who can get the most layers. I will give you an outline of how to do
this, but the details you will have to work out depending upon what
materials you have available. The principle is to have alternating layers of
immiscible solutions with decreasing density starting from the bottom and
going to the top. Use a long glass tube: A large test tube is O.K. but the
larger the tube, the more dramatic the show. Hint: When adding the
solutions, dribble them down a stirring rod to avoid turbulence. Now here is
You want to start with the most dense SOLUTION (either aqueous or
organic liquid) you can find. An example might be a saturated solution of
p-dichlorobenzene (moth balls) in xylene -- do not know the solubility off
hand, but it is large. It may be so great that the density of the saturated
solution may even be greater than the density of solid p-dichlorobenzene
itself, if the spacing of crystal lattice is large (I just do not know.) Both
are available at a hardware store. Or you can start with the most dense
aqueous solution you can find. A saturated solution of Mg(SO4) (Epsom
salts) or CaCl2[density of sat.soln.= ~1.4gm/ml], (sidewalk de-icer)
available at pharmacies or hardware stores, copper sulfate (available at
farm supply stores) You can color any aqueous layer with a drop or two of
vinegar, HCl, NaHCO3, or sodium hydroxide (Draino)[the density of saturated
NaOH is also about 1.4, but you have to handle this carefully], etc. to
change the pH without changing the density, and of course a drop of your
favorite pH indicator (use several if you have them) to get different colors
at the different pH's. If you have some KI available, a drop or two of
tincture of iodine (from the pharmacy) will give an intense blue color from
the I3(-1) ion. Even iodized salt may contain enough iodide to work, but
I've never tried that. Now you just layer the immiscible layers, decreasing
the density of alternate layers by decreasing the concentration of the heavy
component (p-dichlorobenzene or Mg(SO4)) if you select those two components
to adjust the density. Also, you can use glycerin, ethylene glycol, or
propylene glycol to reduce the density of aqueous phases, but you will have
to be careful that the organic solute is insoluble in a contiguous layer.
You can also check the density of urea/water solutions since urea is Note
that the high concentration of salt in the aqueous phases dramatically
decreases the solubility of adjacent water-insoluble phases.
Obviously, the challenge is to find the most colorful combinations of
alternating aqueous and water-insoluble solutions. You can see that using
SOLUTIONS rather than pure liquids gives you a much better handle on
adjusting the density without having to find a new liquid. If your chem lab
has other solvents available, so much the better. You can find the density
of many of the various aqueous combinations in the Handbook of Chemistry and
Hint: Students should practice layering three solutions (A/B/C),
(B/C/D), (C/D/E),... at a time before putting together (A/B/C/D/E/...) to
make sure the densities are correct and that no unexpected mixing makes the
layering fall apart, and that the layers are stable over time (hours or
days). You can check the stability by just letting the tri-samples age. An
indicator such as I2 and pH indicators can diffuse through several layers
because it is soluble in both aqueous and non-aqueous solvents. You should
be aware of that. If the layers are at least 2-5 cm thick diffusion across
adjacent layers will be slow enough.
Click here to return to the Chemistry Archives
Update: June 2012