Chemistry/Forensic Analysis

From WikiEducator
Jump to: navigation, search
Preparation Procedure for Laboratory Experiment

FORENSIC ANALYSIS

Forensic Analysis Preparation — 1

Chemicals For a class of 24 students (12 pairs)

Unknowns Preparation
Sodium chloride 50 g
Sodium bicarbonate 50 g
Sodium carbonate (monohydrate or anhydrous) 50 g
Boric acid 50 g
white sand (fine BUT not flour-like) 50 g
Calcium carbonate 50 g
Cornstarch 50 g
Glucose 50 g
Sodium tetraborate decahydrate (borax) 50 g
Sucrose (“pseudo–amphetamine”) 50 g
Magnesium sulphate heptahydrate (“pseudo–ecstasy“) 50 g
Calcium sulphate dihydrate (“pseudo–heroin”) 50 g
Potassium iodide (“pseudo–LSD”) 50 g
Trisodium phosphate, any hydrate (“pseudo–cocaine”) 50 g

Test Reagents (in 12 droppers each) Preparation
“Iodine solution” 10 g iodine diluted to 100 mL in ethanol
“Vinegar” 5 mL concentrated acetic acid diluted to 100 mL
“10% BaCl2 solution” 10 g of BaCl2•2H2O diluted to 100 mL
“5% Pb(NO3)2 solution” 5 g of Pb(NO3)2 diluted to 100 mL
“10% HCl solution” Dilute 52 mL concentrated HCl to 200 mL
“NaOH solution” Dilute 5.4 g NaOH to 200 mL
“Anthocyanin solution”

(requires 1 L of 70% Isopropyl alcohol)

Mix 500 g of chopped red cabbage with 1 L of 70% isopropyl alcohol, gently boiled for 1 hour to extract the anthocyanin, filtered and boiled down to 100 mL of very deep purple liquid. Keep refrigerated or in freezer between uses.
“Fehling’s Solution A” Dilute 6.93 g of CuSO4•5H2O to 100 mL
“Fehling’s Solution A” Dilute 6.93 g of CuSO4•5H2O to 100 mL
“Fehling’s Solution B” Dissolve 0.44 g of sodium potassium tartrate and 13.0 g of NaOH and dilute to 100 mL
“Buffer” Mix 250 mL of 0.10 M KH2PO4 and 73 mL of 0.20-M NaOH (creates pH = 7.0)
“Bromothymol blue” Dissolve 0.10 g bromothymol blue in 16 mL of 0.010 M NaOH and dilute to 250 mL

Equipment

  • 12 – spatulas
  • 3 – centrifuges
  • 24 – 250 mL beakers
  • 12 – match books
  • 24 – small test tubes
  • 24 – stirring rods
  • 12 – ceramic pads
  • 12 – test tube holders
  • 12 – rubber stoppers to fit test tubes 6–hot plates
  • 12 – evaporating dishes

Forensic Analysis Preparation — 2

Unknowns (Actual Composition)
Note that two unknowns in each set contain two different substances, one of which is soluble in water and one of which is insoluble. Each student will receive three separate unknown samples, labelled as a, b and c.

Note: The chemicals in each sample must be extremely well mixed, grinding them if necessary to guarantee that a “pea–sized” sample contains equal volumes of each substance.

Stock # Insoluble compound Soluble compound Numbers Assigned to Unknowns
1. a sand H3BO3 1, 20, 27
b pseudo–amphetamine (sucrose)
c pseudo–heroin (CaSO4) glucose
2. a CaCO3 Na2CO3 2, 11, 24
b NaCl
c cornstarch pseudo–LSD (KI)
3. a cornstarch NaHCO3 3, 19, 21
b pseudo–cocaine (Na3PO4)
c pseudo–heroin (CaSO4) glucose
4. a sand Na2B4O7 4, 12, 28
b NaCl
c pseudo–heroin (CaSO4) pseudo–ecstasy (MgSO4)
5. a sand H3BO3 5, 18, 25
b pseudo–amphetamine (sucrose)
c CaCO3 Na2CO3
6. a cornstarch pseudo–LSD (KI) 6, 13, 22
b pseudo–cocaine (Na3PO4)
c sand Na2B4O7
7. a cornstarch NaHCO3 7,17, 29
b NaCl
c pseudo–heroin (CaSO4) pseudo–ecstasy (MgSO4)
8. a sand H3BO3 8, 14, 26
b pseudo–amphetamine (sucrose)
c pseudo–heroin (CaSO4) glucose
9. a CaCO3 Na2CO3 9, 16, 23
b NaCl
c cornstarch pseudo–LSD (KI)
10. a cornstarch NaHCO3 10, 15, 30
b pseudo–cocaine (Na3PO4)
c sand Na2B4O7

Forensic Analysis Preparation — 3

Student Unknown Numbers and their Contents

Unknown # Contains Unknown # Contains
1 a = sand + H3BO3

b = pseudo-amphetamine
c = pseudo-heroin + glucose

16 a = CaCO3 + Na2CO3

b = NaCl
c = cornstarch + pseudo–LSD

2 a = CaCO3 + Na2CO3

b = NaCl
c = cornstarch + pseudo–LSD

17 a = cornstarch + NaHCO3

b = NaCl
c = pseudo-heroin + pseudo-ecstasy

3 a = cornstarch + NaHCO3

b = pseudo-cocaine
c = pseudo-heroin + glucose

18 a = sand + H3BO3

b = pseudo-amphetamine
c = CaCO3 + Na2CO3

4 a = sand + Na2B4O7

b = NaCl
c = pseudo-heroin + pseudo-ecstasy

19 a = cornstarch + NaHCO3

b = pseudo-cocaine
c = pseudo-heroin + glucose

5 a = sand + H3BO3

b = pseudo-amphetamine
c = CaCO3 + Na2CO3

20 a = sand + H3BO3

b = pseudo-amphetamine
c = pseudo-heroin + glucose

6 a = cornstarch + pseudo–LSD

b = pseudo-cocaine
c = sand + Na2B4O7

21 a = cornstarch + NaHCO3

b = pseudo-cocaine
c = pseudo-heroin + glucose

7 a = cornstarch + NaHCO3

b = NaCl
c = pseudo-heroin + pseudo-ecstasy

22 a = cornstarch + pseudo–LSD

b = pseudo-cocaine
c = sand + Na2B4O7

8 a = sand + H3BO3

b = pseudo-amphetamine
c = pseudo-heroin + glucose

23 a = CaCO3 + Na2CO3

b = NaCl
c = cornstarch + pseudo–LSD

9 a = CaCO3 + Na2CO3

b = NaCl
c = cornstarch + pseudo–LSD

24 a = CaCO3 + Na2CO3

b = NaCl
c = cornstarch + pseudo–LSD

10 a = cornstarch + NaHCO3

b = pseudo-cocaine
c = sand + Na2B4O7

25 a = sand + H3BO3

b = pseudo-amphetamine
c = CaCO3 + Na2CO3

11 a = CaCO3 + Na2CO3

b = NaCl
c = cornstarch + pseudo–LSD

26 a = sand + H3BO3

b = pseudo-amphetamine
c = pseudo-heroin + glucose

12 a = sand + Na2B4O7

b = NaCl
c = pseudo-heroin + pseudo-ecstasy

27 a = sand + H3BO3

b = pseudo-amphetamine
c = pseudo-heroin + glucose

13 a = cornstarch + pseudo–LSD

b = pseudo-cocaine c = sand + Na2B4O7

28 a = sand + Na2B4O7

b = NaCl
c = pseudo-heroin + pseudo-ecstasy

14 a = sand + H3BO3

b = pseudo-amphetamine
c = pseudo-heroin + glucose

29 a = cornstarch + NaHCO3

b = NaCl
c = pseudo-heroin + pseudo-ecstasy

15 a = cornstarch + NaHCO3

b = pseudo-cocaine
c = sand + Na2B4O7

30 a = cornstarch + NaHCO3

b = pseudo-cocaine c = sand + Na2B4O7


Forensic Analysis Preparation — 4

Note: There are actually only 10 different mixtures, which are distributed as follows.

Mixture Found in the following unknowns
NaCl 2-b, 4-b, 7-b, 9-b, 11-b, 12-b, 16-b, 17-b, 23-b, 24-b, 28-b, 29-b
sucrose 1-b, 5-b, 8-b, 14-b, 18-b, 20-b, 25-b, 26-b, 27-b
Na3PO4 3-b, 6-b, 10-b, 13-b, 15-b, 19-b, 21-b, 22-b, 30-b
sand + H3BO3 1-a, 5-a, 8-a, 14-a, 18-a, 20-a, 25-a, 26-a, 27-a,
CaSO4 + glucose 1-c, 3-c, 8-c, 14-c, 19-c, 20-c, 21-c, 26-c, 27-c
CaCO3 + Na2CO3 2-a, 5-c, 9-a, 11-a, 16-a, 18-c, 23-a, 24-a, 25-c
cornstarch + KI 2-c, 6-a, 9-c, 11-c, 13-a, 16-c, 22-a, 23-c, 24-c
cornstarch + NaHCO3 3-a, 7-a, 10-a, 15-a, 17-a, 19-a, 21-a, 29-a,30-a
CaSO4 + MgSO4 4-c, 7-c, 12-c, 17-c, 28-c, 29-c
sand + Na2B4O7 4-a, 6-c, 10-c, 12-a, 13-c, 15-c, 22-c, 28-a, 30-c

TEACHER NOTES

  1. The tests have been tried exhaustively and appear to work well. This lab is a test of a student’s ability to accurately follow instructions. A student (or pair of student, if desired) should be able to test 3 samples in one hour IF they have been shown how to use a centrifuge properly in the period previous to the lab. Also, in the previous period students should be shown how to read the Instructions and how to interpret the results and what actions to follow. They should be shown how the Flow Chart allows them to keep track of where they are at a given point in the analysis. They should understand that “Analysis is Complete” should be interpreted as “Now start afresh on the next sample”.
  2. IMPORTANT: Students must be instructed that all measurements are approximate, so that “1 mL” can be a bit more or less than 1 mL, for instance, and still give good results. ALSO, to avoid contamination when using 10¬mL graduated cylinders, students MUST wash out a graduated cylinder three times with ordinary tap water before putting a new solution in it.
  3. At the start of the lab period, have one student at each bench get a hot plate, fill a 250 mL beaker 3/4 full of water and set the hot plate on “high”. This is needed for students who have to do Step 9. Warn students that whenever the water boils bown to 1/2 full, they should add extra water using another beaker.
  4. The anthocyanin solution should be kept in the refrigerator until ready to be used. (Storage at room temperature for a week may cause decomposition and changes in the colours.)
  5. The Fehling’s test may give a false positive if reducing impurities are present. If a solution does not turn yellow–orange within about 30 seconds, the result should be considered to be NEGATIVE.

SUGGESTED MARKING SCHEME

2 marks for each substance correctly identified + 2 marks for quality of written descriptions of results

Total = 12 marks