Title: Case Study Tracing Explosives
1Case Study Tracing Explosives
Unit 4 Chemistry of Redox Reactions
2- On May 10, 1979, Nathan Alien left his job at
Bethlehem Steel in Sparrows Point, Maryland, and
got into his 1977 Dodge truck. As Nathan started
the engine, an explosion ripped through the cab
of his truck. Although he survived the initial
blast at 1040 p.m., he passed away at 117 a.m.
in the trauma unit of the local hospital. The
size and scope of the blast led investigators to
believe that a powerful explosive material had
been used in the blast that took Mr. Alien's
life. - Local authorities called on state and federal
agencies to assist in the investigation of this
explosion. Evidence from the bomb scene in
parking lot 7 of the steel mill was sent to a
national laboratory in Rockville, Maryland. The
laboratory, operated by the Bureau of Alcohol,
Tobacco, Firearms and Explosives, was able to
identify the explosive material as Tovex 220, a
brand of dynamite. This information was
important. Further laboratory investigation
found that the dynamite had been manufactured the
previous December and that part of that shipment
went to Jenkins Explosives in Martinsburg, West
Virginia.
3Tracking the TNT. . .
- Investigators traveled to Martinsburg to
interview Lawrence Jenkins, owner of the store
that sold the Tovex 220 dynamite. There they
discovered that on March 10,1979, James McFillin
bought two sticks of dynamite, reportedly for
removing tree stumps. The owner was able to make
a positive identification of McFillin as the
person who purchased the dynamite, and he was
able to describe the vehicle McFillin had driven.
4- The next step of the investigation was to explore
any connection between McFillin and his victim,
Nathan Allan. Investigators were shocked to learn
that McFillin was Nathan's next-door neighborand
uncle! After interviewing family members, it soon
became apparent that McFillin had never accepted
Nathan's friendship with McFillin's wife, Sandra,
and accused them of having an affair. He had made
these accusations before but had never resorted
to violence. However, earlier on the afternoon of
May 10, 1979, James McFillin reportedly had seen
Sandra and Nathan sitting on the front step
talking.
5- After he confronted them with his usual
accusations, Nathan simply returned home. Sandra,
on the other hand, informed James that she was
intending to leave him as soon as their children
were grown. That night, James disappeared for
over an hour before supper with no explanation of
where he had been. Investigators now knew that
McFillin had the means, the motive, and the
opportunity to kill Nathan. James was found
guilty and sent to prison for the murder of his
nephew.
6- How could residue from the explosion provide
investigators with the brand name, manufacturing,
and shipping information for the dynamite? . . .
7Redox Chemistry of Explosives
- 4KNO3 7C S ? 3CO2 3CO 2N2 K2CO3 K2S
- Explosions are nothing more than specialized
combustion reactions. However, they typically do
not rely on oxygen gas from the air. Consider,
for example, the reaction of gunpowder - The carbon component of the reaction is the fuel,
and the potassium nitrate serves as the source of
oxygen in the reaction. Assigning oxidation
numbers to the components of the reaction reveals
that carbon is oxidized (loses electrons) and
that nitrogen is reduced (gains electrons).
Because the fuel source and oxygen source are
both solids and must be physically in contact, it
is critical for the gunpowder to be a homogenous
mixture of fine powders.
8- If there is sufficient oxygen within the molecule
to completely oxidize the carbon and hydrogen
atoms, the compound is said to have a neutral
oxygen balance. A negative oxygen balance exists
when the molecule contains insufficient oxygen
atoms for a complete oxidation reaction a
positive oxygen balance exists when there is a
surplus of oxygen.
- The muzzle flash seen when a gun is fired results
from the hot carbon monoxide gas as it reacts
with oxygen gas from the atmosphere. (Scott
Doyle/Firearms.com)
9Worked Example
- Determine whether the explosive compound RDX has
a positive, negative, or neutral oxygen balance.
Assume an ideal reaction in which all carbon is
converted to carbon dioxide, all hydrogen is
converted to water vapor, and all nitrogen is
converted to nitrogen. Compare the oxygen
needed with that present in the molecule. - SOLUTION The formula of RDX is C3H6N6O6. The
complete oxidation of RDX would be - 3 C atoms form 3 CO2 molecules ? requires 6 O
atoms 6 H atoms form 3 H2O molecules ? requires 3
O atoms 6 N atoms form 3 N2 molecules ? requires
0 O atoms Total O atoms needed 9 - RDX contains 6 oxygen, but 9 are needed. RDX has
a negative oxygen balance and would produce CO,
not CO2.
10Redox is an abbreviation for reduction-oxidation,
- which involve the gain and loss of electrons
between atoms in the reacting compounds. - Oxidation is the loss of electrons reduction is
the gain of electrons. - Oxidation and reduction processes occur
simultaneously.
11Redox reactions. . .
- Many forms of redox reactions can be found, a
common one being the reaction of a metal with an
acid. This particular type of redox reaction is
used to restore serial numbers that have been
altered on guns or vehicle parts.
12Photo (a) shows a gun with its serial number
filed off in an attempt to conceal the gun's
origin. Acid reacts with the iron compressed in
the stamping of the serial numbers, restoring the
pattern of the serial number etchings, as shown
in photo (b).
13- The acid reacts with iron in the steel to produce
Fe2 ions and hydrogen gas. Serial numbers can
be visualized because the hydrogen bubbles tend
to form faster on the steel that was compressed
beneath the serial numbers as compared with the
rest of the surface. The hydrogen gas bubbles
form in the shape of the numbers that have been
removed from the steel. In the reaction below, Fe
becomes Fe2 (in the ionic compound FeCl2), which
involves the loss of two electrons that go to the
two hydrogen ions (H) to form hydrogen gas.
14Redox reactants gain and lose electrons
- Redox reactions also occur when a substance
combines with oxygen atoms during a reaction. An
alternate definition of oxidation is the gain of
oxygen by a substance. It should be noted that
combustion reactions are a type of redox reaction
because the fuel reacts with oxygen.
15LEO goes GER
- Combustion and reduction-oxidation
- Reduction-oxidation
- Gas line explosion
- C3H8 5O2 ? 3CO2 4H2O
Lose Electrons in Oxidation, Gain Electrons in
Reduction
- Battery acid and zinc metal
- H2SO4 Zn ? H2 ZnSO4