in Crime Scene Investigation
T. Trimpe 2006 http://sciencespot.net/
A Few Basics ...
Mixture – Two or more substances that are mixed together, but not
chemically combined.
Examples of mixtures ...
Air – mixture of gases – separate oxygen from nitrogen
Bowl of cereal – mixture of cereal and milk – separate pieces of cereal from the milk
Soda pop – mixture of soda syrup, water, and CO2 gas
Fog – water suspended in air – does it always stay foggy? How does the water
separate from the air?
Kool-Aid – mixture of water, sugar, and flavor crystals
Compounds – Two or more elements that are chemically combined.
Examples of compounds ...
Salt –Sodium and chlorine combined chemically – NaCl
Water –Hydrogen and oxygen combined chemically – H20
Carbon Dioxide – Carbon and oxygen combined chemically – CO2
QUICK CHECK
• Which of these are mixtures?
NaCl
eggs
CaO2
cell phone
KF
• Which of these are compounds?
NaCl eggs
CaO2
cell phone
KF
• How do you know?
• Talk with one other student about your answers…
Solutions
Solutions are mixtures in which one substance is dissolved in another.
Solutions have two parts: SOLUTE and SOLVENT!
The solute is the substance that is dissolved.
The solvent is the substance that does the dissolving
Identify the solute and solvent in each solution ... (answer on your sheet)
Solution
Solute
Solvent
Lemonade
Kool-Aid
Ocean water
Solubility - A measure of how much of a substance will dissolve in a liquid.
* A substance that does dissolve in the solvent is called soluble.
* A substance that does not dissolve in the solvent is called insoluble.
QUICK CHECK
• Which one is the solvent?
The water is dissolving the salt!
• Which one is the solute?
The sugar is being dissolved by the water!
• How do you know?
• Talk with one other student about your answers…
What is Chromatography?
From Wikipedia ...
Chromatography (from Greek word for chroma = color and graphein =
write) lab technique to separate (break apart, divide) mixtures (something
that can be separated)…
Which means ...
Chromatography is the physical separation of a mixture into its individual
components.
We can use chromatography to separate the components
of inks and dyes, such as those found in pens, markers,
clothing, and even candy shells. Chromatography can also
be used to separate the colored pigments in plants.
http://members.shaw.ca/vict/chemistry_test3.htm
QUICK CHECK
• Why do we use chromatography?
• Talk with one other student about your
answers…
Types of Chromatography
Liquid Chromatography is used in the world to test water samples to look for pollution in lakes
and rivers. It is used to analyze metal ions and organic compounds in solutions. Liquid
chromatography uses liquids which may have solids (insoluble molecules).
Gas Chromatography is used in airports to detect bombs and is used is forensics in many
different ways. It is used to analyze fibers on a persons body and also analyze blood found
at a crime scene. Helium gas is used to move a gaseous mixture through a column of
absorbent material.
Thin-layer Chromatography uses an absorbent material on flat glass or plastic plates. It is
used to detect pesticide or insecticide residues in food. Thin-layer chromatography is also
used in forensics to analyze the dye composition of fibers.
Paper Chromatography is one of the most common types of chromatography. It uses a strip
of paper and capillary action is used to pull the solvents up through the paper to separate
the solutes.
Quick Overview…
• Paper Chromatography: You will use water as a solvent to
spread out the solute’s identities.
• You will test different markers and pens to see what they
are made up of using “chromatography”
• Using strips of paper, you will dip the edge of the paper into
the water for 10 minutes without touching the color to the
water.
• The water will dissolve the ink into different colored bands
on the paper – Chromatography!
Paper Chromatography Demo
• We will be using this method of chromatography
during our unit. Watch the short video carefully
(close the ad by clicking on the X).
VIDEO
QUICK CHECK
• What type of chromatography will we use in
this investigation?
• What materials will you need?
Why does a CSI Need to Know About
Chromatography?
Answer this question on your paper…
(Why would a CSI need to use this technique?)
Directions
• Obtain (get) the supplies you’ll need from
your teacher.
–
–
–
–
–
–
Beaker with a small amount of water
Paper strips
Pencil
Markers for testing
Masking tape
Timer
Tape – Label with marker
Pencil
Paper
Ink
•
Cut the strip so that it will be at the correct height – long enough to reach the top level of the
water. Write the pen number on the strip using a pencil or permanent marker.
•
Use one of the testing markers to draw one line on the paper strip at about a 1/2 inch from the
bottom. You don’t want the ink line to touch the water.
•
Tape the top of the strip to a pencil and hang in the water for 10 minutes.
•
Remove the strip from the water and use a pencil to mark the line between the wet and dry
portions of the strip.
•
Allow the strip to dry.
Answer the questions on your guided notes sheet…follow the directions!
Good Luck!