Page 244 - Demo

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Products in this class may be solids, liquids, gases or aqueous solu- tions. Low-molecular aldhydes may be water-soluble, but they are also fammable and likely RCRA characteristic wastes. Excess of leftover aldehyde in an experiment my be oxidized to render it nonhazardous.
Examples
Acetaldehyde and benzaldehyde
Materials Required
Beaker, 1-L
Thermometer
pH paper
Magnetic stirrer/hot plate and stir bar
Potassium permanganate solution, KMnO4, 0.3 M Sodium sulfite solution, Na2SO3, 0.1 M
Sulfuric acid solution, H2SO4, 3 M
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.
Procedure
1
Perform this procedure in a fume hood. Wear chemical splash goggles, chemicals-resistant gloves, and a lab coat or chemical-resistant apron.
2
Dilute any leftover aldehyde with 100 mL.
242
#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
Ice water
Large glass or polyethylene container Stirring rod
Sodium hydroxide solution, NaOH, 3 M or
saturated sodium carbonate solution, Na2CO3 pH paper
Overview
As described above, these substances react with water, and the prod- ucts 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
1
Perform this procedure in a fume hood. Wear chemical splash goggles, chemicals-resistant gloves, and a lab coat or chemical-resistant apron.
2
FLINN METHOD
FLINN METHOD
#2 Aldehydes
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.
3
pH Paper
Potassium Permanganate
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 solu-
tion, 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.
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.
3
Add about 30
mLof0.3M
potassium perman-
ganate solution
over a period of temperature rise 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.
FLINN METHOD #2 continued on next page.
Watch for
NaOH or Na2CO3