TSTL
ETLV-2017/18
Mystery powders
1. Context
Several administrations have received enveloppes containing mysterious white powders. The police is investigating and has
asked you to identify the different powders to determine if everything is a prank or a dangerous situation.
2. Tasks
As chemists, you have to identify the 6 different powders on your desk.
Because their hypothetic toxicity, you are not allowed to smell and taste the powders.
Seq1:
Based on physical and chemical analysis and using only the glassware, apparatus, all chemicals bottles and
objects on your desk (and in the lab), you have first to develop a stategy allowing you to discover the name of
each powder. Write these strategies and protocols on your notebook. What results do you hope for?
Seq2:
Time to lead the different experiments in order to crack the case of the six mystery powders.
Each experiment, each result has to be described (Color, picture, shape, solubility, pH.......)
Seq3:
Each group will make an oral presentation explaining how they have identified their powders. (each group will make
an oral presentation for a different powder)
3. Framework
3.1. According a first investigation, the name of the substances is part of the following list:
Sulfamic acid (Descaling agent), Saccharose (Suggar), Sodium hydrogen carbonate (Baking soda) ,
Methyltheobromine (Caffeine), Sodium sulfate (Plaster), Acetylsalicylic acid (Aspirin), Sodium Chloride (Kitchen
salt), Starch (Cornflour), Calcium carbonate (Powder chalk), Acetyl para amino phenol (Paracetamol).
3.2. Keep the following analytical techniques to lead your experiments
Solubility, Melting point, Ions test, Density, pH measures
3.3. Datas
Name
Solubility
Sulfamic acid
213 g/L
(20°C)
2000 g/L
(25 °C)
87 g/L
(20 °C)
H3NSO3
Saccharose
C12H22O11
Sodium
bicarbonate
Melting point
(°C)
205
Density
(20 °C)
2,13 g·cm-3
pH
<< 7
185,5 °C
1.58 g/cm3
<7
270 °C
2.2 g.cm-3
6.0 <=pH<= 7.5
21,7 g·l-1
235 to 238 °C
1.23 g/cm3
6.0 <=pH<= 7.5
13.9 g/100 mL
(20 °C)
3 mg/mL
(20 °C)
359 g/L
32.4 °C
1.46 g/cm3
6.0 <=pH<= 7.5
135 °C
1.40 g/cm3
<< 7
801 °C
2.16 g/cm3
6.0 <=pH<= 7.5
50 g·L-1
eau, 90 °C
0.013 g/L
200°C
1.5 g/cm3
6.0 <=pH<= 7.5
825 °C
2.75g.cm-3
6.0 <=pH<= 7.5
169 °C
1.26 g/cm3
6.0 <=pH<= 7.5
NaHCO3
Methyltheobromine
Caffeine: C8H10N4O2
Sodium sulfate
Na2SO4
Acetylsalicylic acid
C9H8O4
Sodium Chloride
NaCl
Starch
C6H10O5
Calcium carbonate
CaCO3
Acetyl para amino
phenol C8H9NO2
12.78 g/L
(20 °C)
Laboratory tests