Intro to Chemistry Chem1020 Lab
Observations of Substances
Chemistry Department
Minneapolis Community & Technical College
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Overview
• Part I
Observing physical properties of elements and compounds
• Part II
Observing physical and chemical changes of various
substances
A. Changes caused by fire or heat
B. Changes caused by mixing with other substances
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Part I. Elements and Compounds
Observing and recording physical properties (physical states,
and colors) of elements and compounds
Element: A substance that
cannot be broken down into
other substances by chemical
means and contains only one
element symbol in its formula.
Compound: A substance that can be
broken down into elements by
chemical means and contains more
than one element symbol in its
formula.
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Part I: Cautions!
• Do not open any containers! Some substances are
hazardous.
• When describing a color, try your best.
o If a gas or a liquid does not have any color, you
should record colorless instead of clear or white.
On the other hand, a solid can be recorded as
having a white color.
o Note the subtle difference between the colors of
element iron and element carbon.
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Part II. Physical vs. Chemical Changes
Observing physical and chemical changes of various
substances
• Physical changes do not cause a change in the composition of a
substance. Examples include melting, boiling (or evaporation),
sublimation, etc.
• Chemical changes do result in the formation of new
substance(s) from the original substance(s). The observation of
one or more of the following events may indicate the
occurrence of a chemical change:
o
o
o
o
Color change
Formation of solid (precipitate) from liquid mixture
Formation of gaseous product (bubbles, effervescence)
Burning or combustion
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Part II A
Observing changes of substances caused by fire or
indirect heat
• Your instructor will first demonstrate with ammonium chloride
(NH4Cl) (performed in fume hood) and a copper wire
• Then you will study the following substances in the order:
1.
2.
3.
Use the attached dropper to dispense a liquid sample
Use a metal spatula to dispense a solid sample
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Part II A
1. Add one drop of liquid
(water or isopropyl
alcohol), or a small amount
of sugar (the relative
amount shown on the right)
onto the aluminum foil on
the setup.
2. Approach (not
touch) a lit stick to
the surface of the
substance. Does that
substance catch on
fire? If yes, is it a
physical or chemical
change? Record the
observation.
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Part II A
3. If there is no more fresh sample left
from the previous procedure, add one
drop of liquid or a small amount of solid
onto the same aluminum foil.
4. Using a Bunsen burner, heat the sample
on the aluminum foil from underneath.
Wait until you observe some changes. Is
it a physical of chemical change?
A Bunsen Burner
How to light it up?
See the next slide.
• After you are done with everything in
this part, discard the used aluminum foil
into a designated container.
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How to Light up a Bunsen Burner? An Important Skill in a Chem Lab
1. Connect the burner and the gas
valve with a rubber hose.
2. Gently close the gas valve
of the burner.
5. Approach a lit
stick or a striker to
the top of the
barrel.
4. Turn to open the
gas valve.
Meanwhile quickly
turn on the gas
valve of the burner.
A striker
3. Gently close the air valve
of the burner.
Hottest spot
6. Turn on
the air valve
until you see
two blue
cones formed
in the flame.
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Part II B
Observing changes of substances caused by
mixing five pairs of chemicals.
One of them, the fourth reaction, is shown below:
Used and rinsed
test tubes
(pointing up)
Waste
container
Find clean
test tubes on
your bench.
Use tube #4
for this 4th
reaction.
A pair of chemicals
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Part II B
Mixing Chemicals
1. Choose the correct test tube. Add the
required amount of each of the two
chemicals in that reaction.
2. Make sure not to let the tip of the
dropper touch the test tube (especially
the inside) to avoid contamination. Put
the dropper back to its original container.
3. Mix the chemicals by gently plucking the
bottom of the test tube. Do you observe
any signs of a chemical reaction?
Record the observations.
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Part II B. Waste Disposal
• Don’t mix wastes, or dump them into the
sink!!!
• Empty the content from the test tube into the
designated and properly labeled waste container
which should be at the same station.
• Rinse the test tube with water and dispose of the
rinse into the same waste container.
Waste container
• Put the used test tubes in the test tube
rack for further cleaning.
Distilled water for
rinsing used test tubes
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• Wipe your bench with wet sponge.
• Ask your instructor to sign you out….then you are ready to
leave.
• Finish the lab report (including both data sheet and postlab
questions) after the lab. Feel free to ask instructors questions,
but never ever copy other students’ answers.
• Turn in the lab report the next time when you are expected to
come to the lab.
• Don’t forget to prepare for the next lab before you come next
time.
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