Home/Safety/Laboratory Safety/Chemical Safety/Chemical Hazards/Corrosive Materials

Perchloric Acid

Overview

Perchloric acid (HClO4) is a colorless, odorless, fuming liquid that is miscible with water, extremely corrosive and a strong oxidizer. If your lab

inventory includes perchloric acid, follow these guidelines to protect yourself from injury. Persons working with perchloric acid should be thoroughly familiar with general guidelines for the safe handling of hazardous chemicals supplemented by additional precautions particular for this chemical.

Perchloric acid

Perchloric acid is not only a highly corrosive material it is a strong oxidizer as well. Therefore not only will one need to follow the basic precautions of working with corrosive materials as detailed and outlined in the preceding pages but one will need to follow basic guidelines of working with oxidizers as well. However, perchloric acid only acts as an oxidizing agent when heated or in the anhydrous state (>85%), which then it can be explosive when in contact with organic matter.

Perchloric acid does readily react with metals to form potentially explosive metal perchlorate salts. This is why if perchloric acid is to be used on a regular basis in fume hoods, these fume hoods need to be specially designed and have a wash down feature. Perchloric acid fume hoods are specially designed with this wash down feature as well as other features such as a collection basin and non-reactive furniture (e.g. plastic, ceramic, etc) to reduce metal-perchloric acid interaction. Perchloric acid fume hoods are rare and mostly found in institutions where Geology type work is done – Perchloric acid is heated and used for rock and mineral digestions.

Key take away points for perchloric acid

(in addition to the already stated for Corrosive Materials)

01

Never clean up spills of perchloric acid with spill pads or paper towels. Neutralize perchloric acid first.

02

Store perchloric acid away from metals and organic materials (organic acids).

03

Use secondary containers if you must store perchloric acid with organic acids.

04

Be extremely cognizant of the material (organic, metals, etc) and manner (heating, diluted or concentrated) you use perchloric acid with.

05

Never heat perchloric acid, unless you have special training, as this helps to dehydrate it and makes it more reactive and potentially explosive.

Storage and Handling

Perchloric acid should be used only in standard analytical procedures from well recognized analytical texts. Work with > 85% perchloric acid requires special precautions and should be carried out only by specially trained personnel.
As a minimum, splash goggles, nitrile gloves, and a lab coat should be worn when handling perchloric acid.
Always transfer perchloric acid over a chemical resistant catch tray in order to catch any spills and afford a ready means of disposal.
Precautions should be taken to prevent the buildup of explosive perchlorates. Light, mechanical shock, heat and certain catalysts can be initiators of explosive reactions with the perchlorates that may be formed from perchloric acid. Anhydrous acid which may be formed with strong dehydrating agents decomposes at ordinary temperatures and explodes on contact with most organic materials. Perchloric acid containers should be kept open no longer than 15 minutes per experiment.
Perchloric acid should be stored in well-ventilated locations separated from organic substances and other combustible materials. Do not store perchloric acid in a refrigerator or other dehydrating atmosphere.
Keep incompatible chemicals away from perchloric acid and the area in which perchloric acid will be used. Those chemicals that are incompatible with perchloric acid include oxidizable organic compounds such as alcohols, ketones, aldehydes, ethers, and dialkyl sulfoxides; strong acids such as sulfuric acid; dehydrating agents; anhydrous phosphorous pentoxide; formaldehyde; antimony or bismuth; and reducing agents.
Seventy percent perchloric acid may react with cellulose materials such as wood, paper, and cotton. Preventing contact with incompatible chemicals during storage may be accomplished by placing perchloric acid containers in nonbreakable, chemical resistant containers which are capable of holding the entire contents of the container.

Fume Hoods

Heating of perchloric acid or perchloric acid reactions that involve heat shall NOT be conducted in a general purpose fume hood. A special perchloric acid hood is needed for these experiments.

Use of perchloric acid (<72%) at ambient temperature may be conducted in a general purpose fume hood if the following procedures are followed:

Only small quantities are used on an infrequent basis.
Easily accessible areas in the fume hood, which are exposed to perchloric acid, are immediately wet wiped or rinsed with a squirt bottle of distilled water after use. This procedure prevents the buildup of explosive perchlorates. Periodic methylene blue tests should be conducted after each perchloric acid use for the presence of any perchlorates.

Perchloric acid fume hoods

Heating of perchloric acid or perchloric acid reactions that involve heat shall NOT be conducted in a general purpose fume hood. A special perchloric acid hood is needed for these experiments.

01

Anhydrous perchloric acid is a powerful oxidizer that may explode if it comes in contact with organic materials. Anhydrous perchloric acid can be produced when heating perchloric acid, during the evaporation of perchloric acid, or during reactions involving dehydrating agents.

02

The wash down system should be turned on immediately after perchloric acid has been heated in the hood or after general use of the fume hood. Step by step instructions should be written on how to operate the wash- down for perchloric acid hoods.

03

Chemicals that are incompatible with anhydrous or hot concentrated perchloric acid include acetic anhydride, acetic acid, aniline, carbon (wood charcoal & carbon black), paper, wood, fiber, or sawdust.

04

Tests shall be conducted for explosive perchlorates before any inspection, cleaning, maintenance, or other work performed on the exhaust system or hood interior.

05

Procedures involving heated perchloric acid, reactions involving dehydrating agents, or routine use of perchloric acid must be conducted in a perchloric acid fume hood equipped with a water wash-down system.

In the event of exposure

In the event of skin contact, immediately wash with soap and water and remove contaminated clothing. Seek medical attention immediately.

In case of eye contact, promptly wash with copious amounts of water for a minimum of 15 minutes (lifting upper and lower lids occasionally) and obtain medical attention.

If perchloric acid is ingested, obtain medical attention immediately. If large amounts of this compound are inhaled, move the person to fresh air and seek medical attention at once.

Spills

01

Spill control materials should be available to control the release of perchloric acid. Appropriate protective equipment for clean-up should be worn (i.e., lab coats, protective gloves, protective rubber boots).

02

Perchloric acid spilled on the floor or bench top represents a hazard since the evaporation of the spill may lead to the formation of more dangerous concentrations of the acid. It should not be mopped up, nor should it be soaked up with dry combustibles.

03

Remove all combustibles from the surrounding area (i.e., wood, paper, oils). A water spray may be used to help reduce vapors and keep the area wet. Measures should be taken to keep the material or spill areafrom drying. Neutralize the spill with a dilute solution of sodium bicarbonate and then use absorbent material such as universal pads or absorbent clay to absorb it. Place the material in closed flammable waste disposal can.

04

The area of the spill should be thoroughly rinsed once again and tested for the presence of perchlorates. You may want to neutralize this area also.

Hazardous waste disposal

Excess perchloric acid and waste material containing perchloric acid should be placed in a glass reagent container and labeled as Hazardous Waste.