flinnsci.com SAFETY REFERENCE CHEMICAL DISPOSAL PROCEDURES
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FLINN METHOD
#12a Oxidizing Agents
Strong oxidizing agents, such as chlorates, permanganates and chromates, are
hazardous when in contact with combustible materials. They should never be
discarded with general refuse as they may cause fires or form explosive mixtures.
Oxidizers are classified as characteristic hazardous wastes by the EPA due to
their ignitability, (i.e., their ability to add oxygen to and sustain or intensify a fire
involving a combustible material). Examples include nitrates, inorganic peroxides
and permanganates.
Solid oxidizers will require licensed hazardous waste disposal. Leftover solutions
of oxidizers remaining at the end of an experiment may be reduced as part of
the experimental procedure to render them nonhazardous and suitable for drain
disposal. Sodium thiosulfate is the recommended and most commonly used
reducing agent for this purpose. Note that in the case of chromates, however, the
reduced product will still require licensed hazardous waste disposal due to the
chromium content. See Flinn Disposal Method #27f.
Examples
Bromine, iodine, sodium chlorate, potassium permanganate, sodium chromate
Materials Required
Sodium hydroxide solution, NaOH, 1 M
Sodium thiosulfate solution, Na2S2O3, 4%
Sulfuric acid, H2SO4, 1 M
Glass stirring rod
Large glass beaker
pH paper
Overview
Oxidizing agents by definition oxidize other substances (i.e., they readily react with
substances in low oxidation states to raise them to higher oxidation states). The
oxidizing agent itself is reduced in this process.
The complementary processes of oxidation and reduction are often accompanied
by the evolution of considerable heat. Leftover solutions of oxidizing agents may
be reduced as part of an experimental procedure to render them nonhazardous.
Leftover oxidizing agents in solution may be safely reduced with sodium
thiosulfate. The reactions proceed best in mildly basic, neutral, weakly acidic
solutions. (Too much acid will react with the sodium thiosulfate directly, precipitating
elemental sulfur from the mixture.) In the following example, thiosulfate ions react
with the bromate ions to produce nonhazardous sulfate and bromide ions. Excess
acid must be neutralized with base prior to drain disposal, if allowed.
3H2O + 3S2O3–2 + 4BrO3¯ → 6SO4–2 + 4Br¯ + 6H+
Procedure B: Disposal of Silver Salts
Procedure
1b
Wear chemical splash goggles, chemical-resistant gloves and a lab coat or
chemical-resistant apron.
2b
Dissolve the silver salt in water in a beaker.
5b
Allow the precipitate to dry and dispose of it via licensed hazardous waste disposal.
6b
Check the supernatant liquid for residual silver, and rinse it down the drain with a
20-fold excess of water.
1
Perform this procedure in a fume hood. Wear chemical splash goggles, chemicalresistant
gloves and a lab coat or chemical-resistant apron.
2
This method is for small quantities of
laboratory oxidizing agents only. Add
the oxidizing agent to a twofold molar
excess of a 4% aqueous solution of
sodium thiosulfate (hypo) with continuous
stirring.
Flinn Method #11, continued
FLINN METHOD #12a continued on next page.
3b
Add a 50% molar excess of sodium
chloride solution and stir to ensure
complete mixing.
NaCl
4b
Decant or filter the resulting
precipitate of silver chloride.
4% Na2S2O3
Please… Read the Narratives
Important narratives precede these specific chemical disposal methods!
Please read each narrative carefully! Do not use these procedures if you are
not comfortable with the chemistry. Do not use these procedures without
first consulting with your local government regulatory
officials. These
procedures may not be used in some jurisdictions. All procedures involve
some hazards and risks. Once again… read the narratives that precede
these specific chemical disposal methods.
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