Classification of Matter
Adapted from http://www.arborsci.com/cool/exploring-matter-chemistry-demonstrations
Matter is anything that has mass and takes up space (has volume). We can separate the matter
that we know about into two huge categories: mixtures and pure substances.
Mixtures are physical combinations of at least two pure substances. Most of us are much more
familiar with mixtures than pure substances and they are indeed much more common in our
everyday experiences. For more on mixtures, check this out:
http://www.factmonster.com/ce6/sci/A0833482.html.
Mixtures can be further categorized into homogeneous and heterogeneous mixtures.
Homogeneous mixtures are mixtures with the same composition throughout. Let’s say you stir
some powdered Kool-aid mix into a pitcher of water. Once the powder is dissolved, doesn’t that
Kool-aid look and taste the same from the first sip to the last?
Compare that to some orange juice with pulp in it. Let’s say your brother never shakes up the
carton when he pours himself a glass of juice. By the time you get it, there is a huge blob of
pulp at the bottom of the carton. Now your glass is a combination of juice and big globs of pulp.
That, my friend, is a heterogeneous mixture and a gross one at that. Heterogeneous mixtures
are not uniform in composition at all.
Now, what are pure substances? These are either individual elements right from the Periodic
Table or compounds (chemical combinations of those elements). The element Iron, for
example, is a pure substance.
Student Activity:
This is a station-based activity so you’ll need lots of lab space and a place for students to walk
around in small groups. Collect items like the following (and/or add your own!) and place them
around the lab benches. Ask the students to:
1) Identify the category of matter:
a. Is it a pure substance? If so then is it an element or is it a compound?
b. Is it a mixture? If so, then is it a heterogeneous mixture or homogeneous mixture?
c. (Optional) Have the students write down the criteria they use for their
categorization schemes.
1
Devise a separation strategy for any mixtures found. In other words, if you think you’ve spotted
a mixture, how would you separate it into different components, and (if possible) all the way to
the pure substances that comprise the mixture? (Remember, pure substances cannot be
separated by physical means.)
Suggested Items:
1. Aluminum foil: (Pure substance, element)
2. Lucky Charms: (Heterogeneous mixture.) Separate physically. Visually identify the cereal
from the sugary charms and manually sort into two piles. Separation beyond this is too difficult.
3. Orange juice with pulp: (Heterogeneous mixture.) Separate by gravity filtration of the pulp.
4. Salt water: (Homogeneous mixture.) Separate by boiling away or evaporating the water and
leaving the salt crystals behind.
5. Salt, sand and water: (Heterogeneous mixture.) Separate by filtering out the sand, boiling off
water and leaving salt crystals behind.
6. Reddi Whip dessert topping: (Homogeneous mixture.) Separate gas from solid portion by
heating it. Gas will bubble out since less soluble at higher temps, leaving solid portion behind.
Separation beyond this is too difficult.
7. Oil and vinegar salad dressing:(Heterogeneous mixture.) Separate by difference in
density. (A separatory funnel is a good tool for this.)
8. Chocolate Silk Jif: (Homogeneous mixture.)Separation strategy: good luck J Some
homogeneous mixtures are so uniform, even at the microscopic level, they seem extremely
difficult to separate by conventional means.
2
9. Aspirin (make sure this is pure aspirin with nothing added, like buffers or anything else):
(Pure Substance, compound – acetylsalicylic acid. All aspirin is this compound. People buy
different aspirin products for different reasons. Buffered aspirin helps those prone to stomach
upset, etc…)
10.Iron and Sulfur
(literally iron filings and powdered sulfur): (Heterogeneous mixture) Separate by difference in
magnetic properties.
3