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Case Study Tracing Explosives

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After he confronted them with his usual accusations, Nathan simply returned home. ... James was found guilty and sent to prison for the murder of his nephew. ... – PowerPoint PPT presentation

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Title: 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
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