| Chemicals:
|
| propanone
| | 2-butanone
| | 2-pentanone
| | 1 M aqueous sodium metabisulfite solution |
Apparatus and glass wares:
| magnetic stirrer
| | magnetic stirring bar
| | stirring bar remover
| | Dewar vessel (500 mL) with plastic cover, suitable for magnetic stirrer
| | temperature probe
| | 3 volumetric pipettes 25 mL
| | 4 measuring pipettes 10 mL
| | pipette bulbs
| | disposal container | |
Hazards and safety precautions:
 |
propanone, 2-butanone and 2-pentanone may be harmful by ingestion, inhalation or through skin contact.
|
Safety glasses and protective gloves should be worn. Good ventilation required.
Theoretical background:
The characteristic reaction of aldehydes and ketones is addition across the carbon-oxygen double bond. The difference in
electronegativity between carbon and oxygen results in polarization of the carbonyl group and this polarization directs the
orientation of addition to aldehydes and ketones.
Addition of bisulfite to propanone
Because the reaction is exothermic, it can be controlled by temperature measurement.
Experimental procedure:
Fig. 1: Experiment set-up |
The temperature probe is connected to the input Sensor2 of the CHEMBOX.
The Dewar vessel is fitted with a stirring bar. First, ketone and ethanol are pipetted into the Dewar vessel. Afterwards the
aqueous sodium metabisulfite solution is added while stirring.
| Experiment 1
| 25 mL propanone
| 25 mL ethanol
| 25 mL metabisulfite solution
| | Experiment 2
| 30.6 mL 2-butaone
| 30.6 mL ethanol
| 25 mL metabisulfite solution
| | Experiment 3
| 36.1 mL 2-pentanone
| 36.1 mL ethanol
| 25 mL metabisulfite solution |
A plastic cover (fitted with a temperature probe) is placed on the Dewar vessel. Immediately the sensing software is started.
The real-time graph of the temperature rise is shown on the screen (Fig. 2). The temperature is recorded until
the maximum temperature is reached.
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