| time
requ.: |
45 minutes. |
|
objective: |
detecting
functional groups |
| material: |
- 2 beakers 100ml
- magnetic stirrer
- magnetic stirring bar
- spatula 10mm for powders
- test tubes d=18mm
|
- test tube stand
- stopper
- graded cylinder 50ml
- 2-5 teat pipettes
|
| chemicals: |
|
|
- ceric ammonium nitrate
 
|
- ethanol
|
- lactic acid
|
- sodium hydroxide
- nitric acid c=2mol/l
|
|
preparation 1: |
Note: adapt
volume of stock solution to the estimated number of tests you plan. For
about 30 tests: Prepare a
stock solution of reagent by dissolving 10g ceric ammonium nitrate in 25ml
of nitric acid. |
|
procedure 1: |
Dilute 1ml reagent with 2ml water. Add 5 drops
of unknown sample,shake. |
|
observation 1: |
First the
colour changes from yellow to red, then gas bubbles rise up. A typcial
aldehyd smell and decolourization develop. |
|
interpretation 1: |
CH3CH(OH)COOH + 2 Ce4+ ---> CH3CHO + CO2 +
2 Ce3+ + 2H+
lactic acid
cerium ion acetaldehyde
carbon dioxide cerium ion proton |
|
preparation
2: |
Note: adapt
volume of stock solution to the estimated number of tests you plan. For
about 50 tests: Prepare stock solution by
dissolving 0.01g bromothymol blue and 0.3g sodium hydroxide in 50ml ethanol. |
|
procedure 2: |
To
1ml reagent add 1ml of the unknown sample. |
|
observation 2: |
The colour
changes from blue to yellow/orange. |
|
interpretation 2: |
The sample
contains a carboxylic group. |
|
disposal of: |
Organic
solvents. |
|
source: |
Barke, H.-D. et al.: One Hundred
Chemistry-Experiments to Avoid Chalk and Talk; Univ. of Muenster,
2004. |
