Big Question: How
does matter relate
to atoms, elements,
& the periodic table?
Goal: How can we tell the difference between
a mixture and a pure substance?
Scenario:
 You are a scientists working in a university chemistry lab
in the year 1799. You are trying to understand why some
substances are considered pure substances while others
are referred to as mixtures. You know a pure substance
is defined as a sample of matter with a constant
composition that has distinct chemical properties.
Additionally, you know a mixture can be defined as two or
more substances that have been combined, but each
substance retains its own chemical identity. You are
wondering if salt is a pure substance or a mixture. You
also want to figure out if sand is a pure substance or a
mixture. You decide to conduct an investigation to find
out.
Topic: Mixtures vs. Pure Substances
 Questions:
Page 41
 Notes:
 Write a
testable
question
based on the
scenario on
page 41 of
your science
notebook.
Page 41
Topic: Mixtures vs. Pure Substances Page 41
Notes:
 A pure substance:
 A mixture:
 Cannot be separated
into 2 or more
substances
 Can be separated into 2
or more substances
 Is homogeneous
(uniform composition)
 Heterogeneous
substances (non-uniform
composition)
 Its properties are
constant throughout the
whole sample
 Has constant chemical
composition
 Displays the properties of
the pure substances
making it up
 Its composition can be
varied (changed)
Page 41
Mixture vs. Pure Substance Lab:
 Pre-Lab Observations:
 Examine the sand mixture using a magnifying
glass. Can you observe grains of salt among
the grains of sand mixture?
 Take a picture of the grains through the
magnifying glass using your iPad.
Mixture vs. Pure Substance Lab:
Filtration procedure:
1.  Add water to the mixture and stir until the salt dissolves.
2.  Place a funnel in the mouth of a second clear plastic cup.
3.  Fold a circle of filter paper into quarters and open it into a funnel
shape.
4.  Place the filter paper into the funnel.
5.  Pour the mixture slowly into the paper funnel to filter out the sand.
6.  After filtering the entire mixture, pour the contents of the clear plastic
cup into a plastic tray.
7.  Evaporate the water to re-crystallize the salt. You can place the pie
pans on hot plates or in an oven, or leave them out overnight to dry
out.
Mixture vs. Pure Substance Lab:
Post-Lab Observation
 Sand Grains
Observations:
Page 40
 Evaporated water
Observations:
1.  Take a picture of the grains  Take a picture of the
evaporated water in the
through the magnifying
tray.
glass using your iPad.
 Examine the evaporated
2.  Examine the left over sand
water in the tray. Can
in the cup. Can you still
you observe any salt?
observe grains of salt?
 Write your observations
3.  Write your observations on
on page 40 of your
science notebook!
page 40 of your science
notebook!
Page 40
Conclusion:
 Explain:
 How does this lab prove that salt is a pure
substance but the sand is a mixture?
 Use your notes on page 41 to help you come
up with an answer.
 Email your response to Mr. Colestock:
 [email protected]
Mixture vs. Pure Substance Lab:
Before:
After: