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FLINN METHOD
#2 Aldehydes
Products in this class may be solids, liquids, gases or aqueous solutions.
Low-molecular aldhydes may be water-soluble, but they are also fammable and
likely Resource Conservation and Recovery Act (RCRA) characteristic wastes. Excess
of leftover aldehyde in an experiment my be oxidized to render it nonhazardous.
Examples
Acetaldehyde and benzaldehyde
Materials Required
Potassium permanganate solution, KMnO4, 0.3 M
Sodium sulfite solution, Na2SO3, 0.1 M
Sulfuric acid solution, H2SO4, 3 M
Beaker, 1-L
Magnetic stirrer/hot plate and stir bar
pH paper
Thermometer
Overview
The carbonyl group in an aldehyde is easily oxidized to a carboxylic acid, which is
usually less toxic, less volatile and more water-soluble than the starting aldehyde.
Oxidation can be achieved using aqueous potassium permanganate, and
the reaction can be followed by monitoring the color change. As the
oxidation occurs, the purple permanganation (MnO4¯) is reduced to brown, insoluble
manganate dioxide. The oxidation of benzaldehyde, for example, leads to benzoic
acid and its salt:
3C6H5CHO + 2KMnO4 → 2C6H5CO2K + C6H5CO2H + 2MnO2 + H2O
The reaction may need to be heated, and any excess permanganate should be
reduced by sodium sulfite before disposal. The mole ratio is two moles of permanganate
ion per mole of carbonyl group.
FLINN METHOD
#1b Water-Reactive Metal Halides
Products in this class may react vigorously with water. The reactions generate heat
and the reaction products are strongly acidic. Water-reactive metal halides may be
decomposed to products suitable for flushing down the drain by reacting them with
a large excess of cold water and neutralizing the resulting acidic solution.
Examples
Aluminum chloride (anhydrous) and tin(IV) chloride
Materials Required
Sodium hydroxide solution, NaOH, 3 M or saturated sodium carbonate solution,
Na2CO3
Ice water
Large glass or polyethylene container
pH paper
Stirring rod
Overview
As described, these substances react with water, and the products are acidic. For
example:
SnCl4 + 2H2O → 4HCl + SnO2
The HCl formed will dissolve in the excess water. It is neutralized with either
sodium hydroxide (to form sodium chloride and water) or with sodium carbonate
(to form sodium chloride, gaseous carbon dioxide and water).
Procedure
Procedure
1
Perform this procedure in a fume hood. Wear chemical splash goggles, chemicalsresistant
gloves and a lab coat or chemical-resistant apron.
1
Perform this procedure in a fume hood. Wear chemical splash goggles, chemicalsresistant
gloves and a lab coat or chemical-resistant apron.
2
Prepare an ice/water slush in a large glass or polyethylene container. Slowly add
the water-reactive metal halide directly to the ice/water slush with constant stirring.
Aluminum chloride reacts vigorously with water. Be cautious to avoid localized
overheating.
4
Check local sewer discharge limits for any metal cation remaining in solution.
Decant the liquid to the drain with a 20-fold excess of water if allowed. The solid
residue may be suitable for landfill disposal if no RCRA toxic metals are present.
2
Dilute any leftover aldehyde with 100 mL.
FLINN METHOD #2 continued on next page.
3
When all the compound has been
added to the water, allow the mixture
to come to room temperature and
neutralize to pH 7 with sodium
hydroxide or sodium carbonate
solution. If you use sodium carbonate
solution, expect some evolution
of carbon dioxide gas during
neutralization. A thick white precipitate
of aluminum or tin(IV) oxide will form.
Let the mixture settle overnight.
NaOH or Na2CO3
pH Paper
3
Add about 30 mL of 0.3 M potassium
permanganate solution over a period
of 10 minutes. If this addition is not
accompanied by a rise in temperature
and loss of purple permanganate
color, then heat the mixture using a
hot plate until the color changes.
Potassium
Permanganate
Watch for
temperature
rise
SAFETY REFERENCE CHEMICAL DISPOSAL PROCEDURES
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