INTRODUCTION TO FORENSIC
CHEMISTRY
•
•
•
•
•
•
1.1 Welcome
1.2 Chemistry, Crime, & the Global Society
1.3 Physical Evidence: Matter & Its Forms
1.4 The Periodic Table
1.5 Learning the Language of Chemistry
1.6 The Most Important Skill of a Forensic
Scientist: Observation
• 1.7 Scientific Method
• 1.8 Case Study Finale: Whose Side Are
They On?
INTRODUCTION TO FORENSIC CHEMISTRY
• Forensics means “of the forum” – for public debates and
trials – can be introduced into legal procedings
– Forensic Science requires knowledge of biology, physics,
geology, psychology, and chemistry, in particular, and more.
• Physical Evidence: Matter & Its Forms
– Matter exists as solids, liquids, or gases
• Liquids resist being compressed
• Gases are compressible
The universe is composed of matter and energy.
Matter is composed of mixtures and pure substances.
In matter: There are two kinds of pure substances and two
kinds of mixtures.
1.3 PHYSICAL EVIDENCE: MATTER AND ITS FORMS
Matter is composed of mixtures and pure substances.
• Mixtures involve a physical blending of two or more
“pure substances.”
– mixtures can be separated into their components by physical
means such as evaporation or filtering
– Homogeneous mixtures have uniform properties and
composition, for example, solutions (KoolAid).
– Heterogeneous - variable composition, and often show
visible differences (Chocolate chip cookies).
1.3 PHYSICAL EVIDENCE: MATTER AND ITS FORMS
• Pure substances have uniform composition (elements and
compounds)
– their components can’t be separated by physical means such
as distillation.
• Pure substances are composed of:
– Elements. These contain only one type of atom. Fe, Na, As,
etc.
– Compounds. These contain two or more types of atoms.
H2O, NaCl, KNO3, etc.
• Compounds are of two types:
– Molecular (covalent bonding), such as water, alcohol,
sugar, or CO2.
– Ionic, such as salt, NaCl, or baking soda, NaHCO3.
A lead (Pb) bullet, a
homogeneous
mixture, contains
traces of impurities
such as bismuth, Bi,
and antimony, Sb.
Add in the dirt here,
and the whole
sample becomes a
heterogeneous
mixture.
Differences are
usually visible.
Figure 1.2 (c), pg. 7
Investigating Chemistry, 2nd Edition
© 2009 W.H. Freeman & Company
Can you sort the elements, compounds and
mixtures?
Identify each of these as a pure substance or a mixture
• then as either an element or a compound or as a homogeneous or
heterogeneous mixture.
Pure: a, b, d
Element: b
Compound a, d
Mixture: c, e
Heterogeneous: c
Homogeneous: e
Solutions are homogeneous.
H2, Fe, salt water, wet sand (SiO2), pure baking soda (NaHCO3), gasohol, icewater (s + l).
Introduction to the Periodic Table
• Symbols for the chemical elements are usually the first letter or
the first and second or first and third letters.
• Examples include H for hydrogen, C for carbon, Ca for calcium,
Zn for zinc, He for helium, and Mg for magnesium.
• Some elements were named by alchemists using Latin:
(These elements were known from antiquity.)
– Na for sodium, K for potassium, Au for gold, and Ag for
silver, Sb for antimony.
– Hg for mercury, Fe for iron, Pb for lead, Cu for copper, Sn
for tin, etc.
• Copper, silver, and gold still occur free in nature.
• You are responsible for knowing the symbol and name for
elements 1-95.
Introduction to the Periodic Table
• The table can be divided into metals, nonmetals, and
metalloids.
– The metals predominate. They conduct heat and
electricity well. Mercury is the only liquid at room
temperature.
– The nonmetals are poor conductors, except for graphite,
C.
– Metalloids include: boron, silicon, germanium, arsenic,
antimony, tellurium, polonium, and astatine. They
conduct electricity at high temperatures.
THE MOST IMPORTANT SKILL OF A FORENSIC
SCIENTIST: Observation and the Scientific Method
• Observation is the most
important skill:
– It is the first step in the
scientific method.
• It requires good judgment
and experience to select
the key evidence at a
crime scene.
Critical thinking is
essential.
• It means being logical,
rational, impartial, and
analytical.
2. How are gases characterized?
A) By small distances between particles that are moving at low speeds
B) By small distances between particles that are moving at high speeds
C) By large distances between particles that are moving at low speeds
D) By large distances between particles that are moving at high speeds
4. A molecule is defined as an atom.
A)True
B) False
6. Sugar in tea is an example of what?
A) A complete mixture
B) An incomplete mixture
C) A heterogeneous mixture
D) A homogeneous mixture