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Flinn Method #2, continued 4
Slowly add additional potassium permanganate solution at 70–80 °C until the purple color does not dissipate. Stir for one hour.
Chemical Disposal Procedures
243
70–80 °C
This procedure produces hydrogen gas, which is an explosion and fire hazard. The procedure also requires ethyl alcohol, another explo- sion and fire risk. Perform this procedure in a fume hood, behind a shield, and with proper safeguards.
Anhydrous alcohols contain very little water and are preferred in this procedure. Use anhydrous ethyl alcohol for sodium or lithium and tert-butyl alcohol for potassium.
Leftover potassium is extremely dangerous due to its reactivity and tendency to form explosive peroxides. Appearance of a crumbly yellow coating indicates the formation of potassium superoxide (KO2). Cutting or handling old potassium may result in a violent explosion. Do not attempt to destroy yellow-coated potassium. Contact a licensed hazardous waste disposal company.
Care must be taken in decomposing leftover alkali metals with alcohol. All the metals must be reacted with alcohol before water is added. Many laboratory accidents and fires have occurred by rushing this procedure and adding water too soon. The water will react with a small piece of metal generating substantial heat that autoignites the flammable alcohol.
Calcium and magnesium are less reactive with water. Leftover calcium is easily disposed of using a large amount of cold water, while excess magnesium requires dilute acid to catalyze the reaction.
Mg + 2H2O + H+ → Mg(OH)2 + H2 Procedure A: For Sodium and Lithium Metal
1a
Perform this procedure in a fume hood. Wear chemical splash goggles, chemical-resistant gloves, and a lab coat or chemical-resistant apron.
2a
Place small pieces of leftover or excess sodium or lithium in a 500-mL beaker and cover with mineral oil.
3a Ethyl Alcohol
Slowly add ethyl alco-
hol (at least 13 mL per
g sodium, 30 mL per
g lithium) to the metal
at a rate to cause a
reasonable hydrogen
evolution. Do not add
the ethyl alcohol too
fast (causing excessive
heat generation). Stir the mixture until all the pieces of metal have dissolved.
FLINN METHOD #3 continued on next page.
5
Allow the mixture to cool to room temperature and acidify to pH 7 with 3 M sulfuric acid. If any purple color remains, add 0.1 M sodium sulfite until the mixture is brown.
6
pH Paper
3M H2SO4
Filter the mixture, if needed, to remove insoluble MnO2, which may be placed in the trash. The remaining solution may be flushed down the drain with a 20-fold excess of water.
FLINN METHOD
#3 Alkali Metals and Alkaline Earth Metals
Materials in this class react with air and water, as well as with alcohols and halogenated hydrocarbons. These metals should not be allowed to come into contact with wastes containing these liquids. Alkali metals are stored in a dry mineral oil to keep them from air. The alka- line earth metals are usually covered with a thin coat of metal oxide which protects them from further oxidation. The alkali and alkaline earth metals are characteristic RCRA hazardous wastes due to their reactivity. Small pieces or shavings of alkali or alkaline earth metals remaining in an experiment may be rendered nonhazardous by careful reaction with an alcohol or water, respectively.
Examples
Alkali metals include lithium, sodium and potassium. Alkaline earth metals include magnesium and calcium.
Materials Required
Class D fire extinguisher or a large bucket of clean, dry sand Large glass beaker
Magnetic stirrer and stir bar; or stir rod
Knife to cut large pieces of metal (optional)
pH paper
Ethyl alcohol, anhydrous (for sodium and lithium) tert-Butyl alcohol (for potassium)
Hydrochloric acid, HCl, 1 M
Sodium hydroxide solution, 3 M
Overview
Alkali metals are very reactive with water to produce a base (e.g., NaOH), hydrogen gas, and heat. They also react with alcohols in a more controlled manner to give similar products. The reaction is slower in alcohol due to the lower acid dissociation constant of alcohol relative to water.
Na + CH3CH2OH → CH3CH2O Na + 1⁄2H2
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.