Case Study Tracing Explosives

1
Case 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.

3
Tracking 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? . . .

7
Redox 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)

9
Worked 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.

10
Redox 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.

11
Redox 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.

12
Photo (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.

• 2HCl Fe ? FeCl2

14
Redox 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.

15
LEO 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