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CH1301 > chemistry against crime > Flashcards

chemistry against crime Flashcards

(59 cards)

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1
Q

what are the 3 steps of the forensic process

A

identification, classification, individualisation.

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2
Q

what are the 2 types of evidence

A
  1. inclusive
  2. exclusive
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3
Q

what is inclusive evidence

A

ensures a person or object remains under study

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4
Q

what is exclusive evidence

A

excludes a person or object from further study.

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5
Q

what is circumstantial evidence?

A

evidence requiring interference to move to a conclusion.

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6
Q

how do you measure the absolute error ?

A

EA = X - X(true)

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7
Q

how do you measure the relative error ?

A

ER = ((X - Xtrue) / Xtrue ) x 100

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8
Q

what does NUSAP stand for to help you quote uncertainties

A

number, units, spread, assessment, pedigree

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9
Q

what does calibration mean ?

A

the comparison of measurement values delivered by a device under test with those of a standard of known accuracy

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10
Q

what does standard mean?

A

object, system or experiment that bears a defined relationship to a unit of measurement of a physical quantity.

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11
Q

what are the 2 main methods of producing alcohol?

A
  1. petrochemically (hydration of ethane)
  2. fermentation (metabolism of sugar by yeast In the absence of oxygen)
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12
Q

how many mg of alcohol does it take to be fully drunk?

A

150-200

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13
Q

how many mg of alcohol in breath to drink in the Scotland ?

A

<22ug / 100ml

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14
Q

what is the process of the metabolism of alcohol in the blood?

A

ethanol -> acetaldehyde -> acetic acid -> CO2 + H2O

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15
Q

what is the wind mark equation

A

calculates the maximum amount of alcohol you could find in someones body.

c = 100 x a/( w x r)

a = amount of alcohol
c = peak concentration of alcohol (mg / 100ml)
w = mass of drinker (kg)
r = windmark factor (0.65 for males, 0.55 for females.)

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16
Q

what are the 4 methods you can use to detect alcohol in someone’s breath

A
  1. chemical oxidation
  2. fuel cell detector
  3. IR absorption
  4. gas chromatography
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17
Q

what is the chemical oxidation method of alcohol testing

A

suspect blows into the metre where 50ml of the breath fills a small chamber which is bubbles through with dichromate. light sensitive detector measures the conversion to chromate

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18
Q

what is the IR absorption method of alcohol testing

A

suspect blows into metre and first portion of breath discarded and final portion captured in gas cell. IR passed through sample and absorption analysis

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19
Q

what are 3 common errors in alcohol breath testing

A
  1. temperature variation
  2. poor calibration of instuments
  3. interfering compounds.
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20
Q

what are the 4 ways drugs can be classified

A
  1. by their origin
  2. by the affect they have on the body
  3. by use
  4. by legislation
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21
Q

what is pharmacokinetics

A

the study of the movement of a drug and its metabolic products through the body

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22
Q

what is the marquis colour test

A

used to identify drugs. each Turning a different colour. heroin = deep purple

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23
Q

what is the duquenois Levine colour test ?

A

test for cannabis.

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24
Q

what is the Scott colour test?

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A

test for cocaine

25
what 2 methods are used for drug profiling ?
gas chromatography mass spectrometry
26
what does mass spectrometry help us determine in drugs
the number of different isotopes in the compound.
27
what's an example of a athlete who was banned due to doping
lance Armstrong, famous cyclist and 7 time winner of the tour de France.
28
what reactions take place in a flame?
we make the products of the combustion reaction, we make many intermediates including C, H, CH4, CHO ... finally we make free radicals. - reactive species with unpaired electrons
29
what is an incendiary device?
devise designed to ignite fire often involving time delay
30
what is headspace analysis ?
it is the analysis of fire debris, trying to detect accelerants.
31
what are the 4 steps of headspace analysis ?
1. fire debris is collected in metal tin with predrilled hole. 2. sealed with airtight seal, trapping residual volatile accelerants 3. gentle heating caused the vaporisation of volatile species 4. gas above the debris is drawn off using syringe though the pre drilled hole
32
how do you analyse the removed gasses from headspace analysis.
mass spectrometry and gas chromatography
33
how does gunshot work ? 5 steps
1. primer is ignited by pulling the trigger 2. ignites the propellant 3. propellant expands, sending high speed pressure waves down the gun 4. propels bullet from the gun 5. if speed of sound exceeded a cracking sound is heard
34
what is the metal test use on gunshot residue
spray exhibit with a weak solution of sodium rhodizonate (orange solution). red/pink colour formed if lead present.
35
what is the difference between deflagration and explosion?
in deflagration the Flames travel at subsonic speeds, which are slower than the speed of sound. Deflagrations are also known as low explosives. explosion is just the general term for a rapid decomposition of a chemical mixture
36
what is the explosive power index
= Q V(explosive) / Q V(picric) x 100 Q = heat produced V = volume of products
37
what are the tests run on explosive residue
identification : gas chromatography mass spectrometry tests for nitrates and nitrites : Griess-type tests dpa test
38
what are griess type tests (tests for nitrites)
treat photographic paper with a mixture of sulfanilic acid and naphthol. place face down on clothing steam iron use acetic acid orange colour formed if nitrite present
39
what is the dpa test (nitrates) for gunshot residue
diphenylamine. add No3- and blue colour will form if nitrate is present.
40
what's the test for screening explosives ( detecting them before they explode)
ion mobility spectrometry
41
what's a taggant
chemical or physical marker added by manufactures to allow testing.
42
what is the process of the drunkometre
subject would breathe into devise and would be pumped though acidified potassium permangate solution. if the solution changed colour it would indicate there was alcohol in their breath. the bigger the colour change the more alcohol present.
43
what is the difference between the primer and the propellant and which would be the easiest to detect in gunshot residue?
the primer is a chemical which ignited the propellant. the primer is easier to detect as there are more methods to detect it such as 1. tests for nitrates and nitrite s 2. tests for metals
44
what is the chain of custody
info on how and when evidence is collected - info of how sample is transported. - info on security when sample is stored. - info on how and when evidence was collected
45
how would you determine if two drugs samples are from the same batch
1. gas chromatography 2. mass spectrometry
46
what is meant by positive bias
systematic error where the answer is consistently higher than the true or actual value
47
why might a measurement by bias ?
contamination instrument errors handling errors
48
what is the units for the answer in the wind mark equation
mg / 100 ml
49
what is meant by the explosive power index
a measure of the explosives material energy output compared to picric acid.
50
why are presumptive tests useful ?
1. test is simple 2. rules out possible conclusions fast 3. easy to do at a. crime scene - these are not good enough evidence to use at court!
51
what is a test for NOx
Griess test - ...
52
what is locards principle
'every contact has a trace'
53
what is the analyte
the compound / thing which is the subject of the analysis
54
what is the matrix
remainder of the compound which the alalyte forms a part of
55
what is the names of the 2 blood tests
Kastle-Meyer and Luminol
56
what would you add to cociane
caffeine
57
what would you add to herion
quinine
58
what does thinner mean
not active, just dilutes the drug
59
what does adulterant
active with similar effects to the drug

CH1301 (7 decks)

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