Safety Reference
Flinn Method #11, continued Procedure B: Disposal of Silver Salts
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.
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                   NaCl
Strong oxidizing agents such as chlorates, permanganates, and chro- mates 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, that is, 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 thiosulfate solution, Na2S2O3, 4% Sulfuric acid, H2SO4, 1 M
Large glass beaker
Glass stirring rod
pH paper
Sodium hydroxide solution, NaOH, 1 M
Overview
Oxidizing agents by definition oxidize other substances; that is, 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 maybe reduced as part of an experimental proce- dure 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 example below, 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
1
Perform this procedure in a fume hood. Wear chemical splash goggles, chemical-resistant gloves, and a lab coat or chemical-resistant apron.
FLINN METHOD
#12a OxidizingAgents
    3b
Add a 50% molar excess of sodium chloride solution and stir to ensure complete mixing.
4b
Decant or filter the resulting precipitate of silver chloride.
   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 down the drain with a 20-fold excess of water.
2
This method is for small quantities of labora- tory oxidizing agents only. Add the oxidizing agent to a twofold molar excess of a 4% aque- ous solution of sodium thiosulfate (hypo) with continuous stirring.
                                                                   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.
                                                      4% Na2S2O3
                                      FLINN METHOD #12a continued on next page.