Conduct a brief review of the past material
by asking the class the following questions:
(Colloids exhibit the Tyndall
effect, whereas suspensions do not. Suspensions often settle out,
whereas colloids do not.)
(Colloids have medium-sized
particles and their particles scatter light. Solutions have very
small particles, cannot be separated through basic filtration, and
their particles do not scatter light.)
“List five physical properties…”
(Answers may vary. Examples include viscosity, density,
conductivity, magnetism, boiling/melting/freezing point,
thermal expansion/contraction, malleability, ductility, surface
tension, volatility, etc.)
Tell students, “Today, you are going to
demonstrate your knowledge of physical properties and mixtures by
completing a lab activity. Each team (lab groups of two to four
students) will be given the same substance. Your task is to separate
the substance into its original components and in their original
state. The substance is made from sand, copper shot (or copper
pieces), iron filings, and salt.”
Have students proceed to the lab stations in
teams of two to four. At each lab station, provide the equipment
listed in the Materials section. Give each student the Separation of
a Mixture activity sheet (S-8-5-3_Separation of a Mixture Student.doc).
Tell students, “You will be given 15
minutes to examine the mystery substance, look over the equipment
provided to you, and fill out Part I of your Separation of a Mixture
lab worksheet.” As a class, discuss the answers to Part
I. Use the Separation of a Mixture–Teacher activity sheet for
answers (S-8-5-3_Separation of a Mixture Teacher.doc). You can have students return to their seats or stay at their
lab stations. They should all be aware that the mystery substance is
a heterogeneous mixture that is classified as a suspension. When
addressing the last question in Part I, say, “Which physical
properties would help you separate this mixture? In what order should
the separation techniques be done?”
Then direct students’ attention to Part II
of the lab handout. In this section, the teams design their own
procedure for separating the mixture. The flowchart will give them an
idea of the order. After 10 minutes, write and discuss the correct
answers on the board.
Once students understand the procedure,
demonstrate proper lab protocol.
Obtain a small evaporating dish of the
Using tweezers, pick the copper shot
from the mixture. Transfer it to an empty weigh boat.
Use a magnet to attract the iron
filings. Sort through the mixture’s layers, as there are filings
at the bottom as well. This may irritate your hands, so gloves will
be available. Scrape the filings off the magnet and into a separate
To separate the sand from the salt, you
will need to add 10–25 mL of water to the evaporating dish. Use
glass stir rods to dissolve all of the salt. Set to the side.
Using filter paper, make a funnel shape
like the one shown below:
Put the funnel-shaped filter paper
inside a funnel and place the funnel on an Erlenmeyer flask.
Pour the sand, water, and salt mixture
through the funnel. Wait until all the water has gone through the
filter and into the flask.
Remove the sand and filter paper from
the flask and lay them on a paper towel to dry.
Pour the salt water into an evaporating
dish and place it on a hot plate (on medium). Watch closely. The
water will boil off, leaving the salt behind. Turn off the hot
Remove the evaporating dish with tongs
or a hot pad. Be careful as the dish is hot.
All glassware can be rinsed with water.
Iron, copper, and sand can be recycled for the next class to use.
If you have covered phase changes, sublimation in particular,
you can add ammonium chloride (NH4Cl) to the mixture.
After students have removed the copper shot and the iron filings,
they can set up a ring stand with a Bunsen burner underneath. They
should place the evaporating dish on a clay triangle and heat the
mixture until it smokes. The white smoke is the ammonium chloride
leaving the mixture. Students should use a glass rod to stir the
mixture every once in a while. Once the smoking stops, the
sublimation of NH4Cl is complete. Let the dish cool until
it is safe to be handled. The remaining separation techniques are