spot tests for explosives Flashcards
(29 cards)
What is fire?
conversion of solid matter to its gaseous form followed by
- rapid oxidation of a gaseous fuel
- rapid release of energy from the exothermic reaction
the heat released in the reaction is called “heat of combustion”
gases are heated to a high temp
gases are soot emit light and heat
Fire triangle
energy, oxidiser, fuel
What is flash point?
lowest temp at which there is sufficient vapour pressure to cause a flammable mixture if ignited by spark or flame
What is fire point?
just above flash point. lowest temp at which a substance continues to burn
What is ignition temp?
minimum temp at which fuel will spontaneously ignite
spark or flame free event
the presence of oxygen is always a requirement
What is an explosive?
common term is a bomb
bomb is any explosive device that typically relies on the exothermic reaction of an explosive substance which will produce an extremely sudden and violent release of energy producing immense quantities of gas
the build up of gas pressure, a confined space is the actual “explosion”. the damage is caused by rapidly escaping gases from confinement.
the ignition of an explosive is called detonation
combustion of explosives occurs so rapidly that there isn’t enough time for the oxygen in the surrounding atmosphere to combine with the fuel
therefore many explosives must have their own source of oxygen or oxidising agents
Types of explosives
explosives are classified as high and low explosives based on their speed of decomposition
in a low explosive, this speed is called the speed of deflagration
in high explosive, it is called the speed of detonation
Is black powder a high or low explosive?
low
What is black powder comprised of?
75% potassium nitrate
15% charcoal
10% sulphur
What is the oxidising agent in black powder?
KNO3
Black powder
volume expansion = 5100x
burns when confined
becomes lethal and explosive when confines
heat applied to powder, oxygen from KNO3 is liberated
combines with the carbon and sulphur
combustion of charcoal and sulphur produces 2 gases (CO2 and SO2)
Are organic explosives high or low explosives?
high
what is the most common compound used in organic explosives?
nitro-compounds
What is nitro-glycerine?
organic explosive
viscous liquid at room temp that explodes violently on agitation
What is dynamite?
nitro-glycerine absorbed into a sol support
Initial extraction of explosive residues
should be done with acetone
extracts both inorganic and organic compounds to a sufficient extent to enable spot tests to be performed
although nitrocellulose and nitrostarch are not truly soluble they form a colloidal solution which can be used
What is used as a spot test for ammonium ions?
nessler reagent
solution made from a mixture of potassium tetraiodomercuate in KOH
what is the positive result for ammonium ions using nessler reagent?
orange/brown precipitate
What is used as a spot test for nitrates?
diphenylamine
diphenylamine reaction of nitric acid proceeds via the oxidation of diphenylamine to the colourless N,N’-diphenylbenzidine
What colour shows a positive result for nitrates when using diphenylamine?
dark blue
what is nitrocellulose?
a constituent of smokeless powder and some dynamites. The ONO2 group of the nitrocellulose can be detected by fusion with benzoin. When heated to 130 degrees vapours formed are tested with paper impregnated with Griess reagent. A positive red stain develops on the paper
What is nitroglycerin?
can be detected using the DPA reagent and H2SO4. a deep violet semiquinoid compound is formed. Selective detection of nitroglycerin is achieved by exploiting its relatively high vapour pressure
Zinc
homemade explosives
diphenylthiocarbazone in an alkaline solution forms insoluble, coloured inner complex salts with many metal ions
magnesium
explosive devices often use magnesium filings or powder.
magnesium salt give a blue precipitate in alkaline solutions of quinalizarine.
