Chapter 2 Guide to Chemical - PowerPoint Presentation

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Chapter 2

Guide

to

Chemical

Hazards

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Chapter Outline

Introduction

Toxicity

Source of InformationThe Properties of Chemicals

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Introduction

Chemicals

and

laboratory intruments

can

harm you if not handled properly

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Introduction

Chemicals

can be classified as

ToxicExplosiveFlamableReactive

Carcinogenic

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Introduction

Some

chemicals can harm you in more than one way

Consider every chemical as hazardous

Degree of hazard vary from one chemical to another

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Introduction

Example

: gasoline and alcohol

Both are flammable, but gasoline is more flammableGasoline ignites easily, burn or explode more vigorously than gasoline

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Introduction

Working with chemicals can be safe if proper precautions are followed

Your laboratory instructor will guide you on how to work safely in the laboratory

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Toxicity

“

What is it that is not poison? All things are poison and nothing is without poison. It is the dose only that makes a thing not a poison

.” Paracelsus

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Toxicity

Any substance could be harmful to living organisms

Hazardous chemical

: any chemical that presents a hazard either under normal use or in a foreseeable emergency (OSHA)

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Toxicity

Factors that affect toxicity are variable:

Dose

(amount of substance to which one is exposedand the length of time of exposure to the substance)

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Toxicity

Route

of exposure

Inhalation استنشاقthrough lungs by breathingIngestion

through digestive system (eating, drinking, chewing gum, smoking, applying cosmetics, using contaminated beaker in lab for drinking, eating with contaminated hands, etc…)

Absorption through body opening (skin, eyes, ears) or Injection

(e.g. contaminated sharp objects)

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Route

of exposure

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Toxicity

Other factors

(e.g. gender, age, lifestyle, allergic factors, genetic disposition, mode, …)

Toxic effects can be immediate or delayedreversible or irreversiblelocal or systematic

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Toxicity

Toxic effects may vary from

Mild

and reversible (e.g headache from inhaling ethyl acetate that disappears with inhaling fresh air, to

Serious

and

irreversible (e.g. birth defects from excessive exposure to a toxic chemical during pregnancy or cancer from excessive exposure to a carcinogen)

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Toxicity

Toxic effects can be:

Acute poisoning

Exposure to a toxic substance that lasts for  24 hOften, the effect is sudden, can be painful, severe, or fatalقاتل

Normally, single exposure is involved (e.g. exposure to hydrogen cyanide, carbon monoxide)

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Toxicity

Chronic poisoning

Repeated esposures with time intervals in months or years

Symptoms may not be immediate (e.g. lead or mercury poisoning, exposure to pesticides or radiation)Substances in combination2 or more hazardous materials are present and the cobined effect is greater than the effect of individual substance

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Toxicity

Examples

:

exposure to alcohol and chlorinated solvents (combined effect)Cyanide and amyl nitrite (antagonistic effect)AllergensSubstances that produce immunologic reactionAsthma-like symptoms or dermatitis

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Toxicity

Generally, toxic effect from a substance is dependent on sevirity of exposure

more severe the results are expected from larger / more frequent exposure

Minimizing exposure means reducing or preventing harm. How to achieve this?

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Toxicity

Ways of Reducing Exposure

Minimize exposure through ingestion

Do not eat or drink in labDo not put your hands or fingers in your mouthWash your hands before leaving lab or if contaminatedWhen in lab keep your hands away from your eyes, ears, or nose unless you wash themDo not touch your skin if injured

Be very careful when working with sharp objects

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Toxicity

Minimize exposure through skin

Use proper gloves

Discard gloves after use and wash your handsMinimize exposure through inhalationLabs should be well ventilatedUse fume hoods/safety cabninets when necessaryIf a chemical is spilled on your clothes or skinWash the affected area immediately and thoroughly with running water

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Sources of Information

Material Safet Data Sheets (

MSDS

)MSDS describes the hazards of a chemical and the precuations that must be taken to avoid harmMSDS should be made available in laboratories for workers and students to read before carrying out any experiment

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Sources of Information -

MSDS

MSDS should at least contain

Name of the hazardous chemical (names with % if mixture)Some of physical and chemical properties (e.g. vapor pressure, boiling point, flash point, density, …)Physical hazards of the substance (e.g. flammable, explosive

, corrosive, …)

Health hazards (e.g. corrosive, irritant, carcinogen, …)

Routes of entry (e.g. inhalation, ingestion)

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Sources of Information -

MSDS

Exposure limits: permissible exposure limit (

PEL) and threshold limit value (TLV) if establishedCan the substance cause cancer or not

Precautions to be taken when using the substance

Control measures, work practices, and PPE

Emergency and first aid proceduresDate of preparation / revisionName of manufacturer and address

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Sources of Information -

MSDS

Examples on MSDS

Acetone

Nitric acid

Water

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Sources of Information -

MSDS

Understanding an MSDS

CAS registry no: a unique number assigned to each chemical by ACS CAS (Chemical Abstracts Service)Ceiling limit: concentration in ppm or mg/m3

that must not be exceeded in a specified time period (typically 15 min)

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Sources of Information -

MSDS

Chemical name

: IUPAC, CAS, common chemical name Example: 1,2-ethanediol (IUPAC) or ethylene glycol (common)Composition of mixtures: includes all hazardous components present in concentrations >1% and all carcinogens in concentrations >0.1%

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Sources of Information -

MSDS

Control measures

: list types of PPE (e.g. lab coats, glove, respiratory equipment) , fumehood, glovebox, safety cabinit, etc…Fire and explosion hazard data: Flash point: “lowest temperature at which the vapor of the chemical can be ignited by a flame when the chemical is slowly heated in a special apparatus”

Autoignition temperature

: “lowest temperature at which a chemical ignites spontaneously in the air”

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Sources of Information -

MSDS

Flammable limits

: volatile flammable chemicals have min and max vapor concentrations in air below and above which they cannot be ignited. Increase in temperature decreases the lower flammable limit and increases the upper limit. Increase in pressure decreases the lower flammable limit and increases the upper limit. Recommended extinguishing media: some chemicals (e.g. Mg) ignites more vigorously when in contact with water ro carbon dioxide.

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Sources of Information -

MSDS

First Aid

: describes procedures of emergency first aid. Perform the first aid if qualified, call the ambalance.Health Hazard Data: Lethal Dose Fifty (

LD

50

) Lethal concentration Fifty (

LC50)

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Sources of Information -

MSDS

LD

50 (lethal dose fifty) is the lethal single dose (usually by ingestion) in mg of chemical per kg of animal body weight that is expected to kill 50% of the test animal population within a specified time.

LC

50

(lethal concentration fifty) is the lethal concentration of a chemical in air expressed as ppm of gases and vapors or as mg/L of air for dusts and mists expected to kill 50% of the test animal population within a specified time by inhalation.

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Sources of Information -

MSDS

Permissible exposure limit (PEL)

: concentration of a hazadous chemical in the air in ppm or mg/m3. It is the max concentration in the breathing air that can be inhaled without harm by an adult worker for 8 h a day, 40 h a week, during his/her working lifetme – provided that the worker is a person of average healt.

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Sources of Information -

MSDS

Physical/chemical properties

: Boiling point Melting point

Vapor pressure

Specific gravity

Solubility

Appearance and odor: liquid, solid, or gas (at room temperature); color, crystalline, or amorphous; etc.. Evaporation rate

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Sources of Information -

MSDS

Precautions for spills and cleanup:

describes how to properly cleanup of a spill or release (can it be put in a landfill or an approved disposal facility).Reactivity: some chemicals react vigorously with other chemicals; others are self-reactive or unstable and decompose vigorously if disturbed. Short-term exposure limit

(STEL): concentration in ppm or mg/m

3

that should not be exceeded for more than a short period (usually 15 minutes).

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Sources of Information -

MSDS

Target organ:

name of an organ(s) (kidney, liver, skin, eyes, etc.) or system(s) (respiratory system, central nervous system, etc.) that are likely to be adversely affected by an overexposure to the chemical.Time-weighted average (TWA): worker’s exposures are to be measured and averaged over an 8-hour day. If the TWA does not exceed the PEL or TLV for a worker, then he or she is not harmed.

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Sources of Information -

MSDS

Threshold limit value

(TLV): this number is a concentration limit (similar to PEL). PEL limit is a legal limit; the TLV limit is a voluntary, recommended limit.

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Sources of Information -

Labels

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Sources of Information -

Labels

Lables on bottles of chemicals provide critical information about the chemicalLabel should contain:name of the chemical;one of 3 signal words: Danger

,

Warning

, or Caution, to indicate the relative degree of severity of the hazard(s) of the chemical;

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Sources of Information -

Labels

Danger

: signifies that the hazards can cause serious injury (e.g., blindness, loss of a limb) or death. Warning: signifies that the hazards can cause less than serious injuries.

Caution

:

warns users to be careful when using, handling, or storing the chemical

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Sources of Information -

Labels

main foreseeable hazard(s) when used;precautionary measures that will protect users from the harmful effects of those hazards;first aid instructions;instructions in case of fire, if applicable;

methods to handle spills or leaks, if appropriate;

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Sources of Information -

Labels

instructions if the chemical requires unusual handling and storage procedures; and name, address, and telephone number of the manufacturer or supplier

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Hazards and their Ratings

Hazard

Type

Hazard Rating

Health

Hazard

0 - Ordinary combustible hazards in a fire1 - Slightly hazardous

2 - Hazardous3 - Extreme danger4 - DeadlyFlammability

Hazard

0 - Will not burn

1 - Will ignite if preheated

2 - Will ignite if moderately heated

3 - Will ignite at most ambient conditions

4 - Burns readily at ambient conditions

Reactivity

Hazard

0 - Stable and not reactive with water

1 - Unstable if heated

2 - Violent chemical change

3 - Shock and heat may detonate

4 - May detonate

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How to Read

MSDSs

and

LabelsPages 16 - 20

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MSDS & Properties of Chemicals

MSDS

provide also other useful information about chemicals (e.g. solubilities, volatility, reactivity, classification of chemicals)

Examples:Reactivity of Chemicals

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MSDS & Properties of Chemicals

Reactivity of Chemicals

MSDS provides information on the

incompatibility of chemicalsExample: adding acetic acid to an oxidizing agent (e.g. chromic oxide, nitric acid, perchloric acid, potassium permanganate) produces a vigorous reaction. If reaction conditions are not minimized (e.g. quantity, temperature) the reactioncould be disastrous.

Acetic acid could not be stored near

an oxidizing agent.

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MSDS & Properties of Chemicals

Differing solubilities in water

Knowledge of differing solubilities in water and other solvents helps you decide how to dissolve a substance

Examples: All nitrates are soluble in waterSome chlorides and sulfides are soluble in waterSome of the insoluble chlorides are slightly soluble in warm water

Solubility of some sulfides varies depending on pH

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Properties of Chemicals

Classifying Hazardous Chemicals

All chemicals are hazardous in one way or another

You must know the hazards of each chemical before dealing with itTo facilitate knowledge about hazards of chemicals, chemicals are classified in groups

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Class

Examples

Oxidizing agents

Nitrates, permanganates, chromates

Reducing agents

Hydrogen, carbon, hydrocarbons, organic acids

Corrosive chemicals

Strong and some weak acids and bases, halogens

Water-reactive chemicals

Alkali metals, some hydrides, phosphides, carbides

Air-reactive chemicals

Alkali metals

Highly toxic chemicals

Carcinogens, cyanides, phenol

Less toxic chemicals

Ethanol,

n

-hexane, acetic acid

Self-reactive chemicals

Picric acid, TNT, diazo compounds

Incompatible pairs

*

Acid vs base, oxidizing agent vs reducing agent

*

Refer to Appendix 2 for more examples

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Properties of Chemicals

Solvents and Their Hazards

Examples of some solvents

WaterOrganic solvents (methanol, hexane, ether): mostly flammableFlammable solvents do not burn; their vapor burns

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Properties of Chemicals

Solvents and Their Hazards

More

rate of vaporization produces more flammable vaporsVaporization increases with temperatureAll flammable liquids and solids must be kept away from oxidizers and ignition sources

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Properties of Chemicals

Vapors of all organic solvents are toxic

Some symptoms from overexposure to organic solvent vapors:

dizziness, slurred speech, unconsciousness and, rarely, deathSome organic solvents can penetrate intact skin and cause dryness and cracking

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Properties of Chemicals

Affected organs:

central nervous system, liver, kidneys

Some organic solvents (e.g., ethers, some non-aromatic unsaturated cyclic hydrocarbons) can form potentially explosive peroxidesThese solvents are particularly dangerous if they are evaporated close to dryness

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Properties of Chemicals

Acids and Bases

Corrosive

: all strong acids and bases, some weak acids, some slightly soluble basesIrreversibly destroy living tissue (e.g. eye, skin) when come in contact withDistruction increaes with concentration and contact timesome acids/bases start damaging within 15 s of contact

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Properties of Chemicals

HX acids:

aqueous solutions are toxic

vapors are serious respiratory irritantsHF’s vapors or aquous solutions are : ToxicRapidly absorbed through the skin, penetrating deeply and destroying the underlying tissues

Contact with dilute HF is usually painless for several hours, but then serious burns appear along with adverse internal effects and extreme pain

Be well prepared before using HF

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Properties of Chemicals

Sulfuric acid

(H

2SO4) Very strong dehydrating agent when concentratedDilute solutions are oxidizing agentsFuming sulfuric acid is a strong oxidizing agentWhen preparing aqueous solutions

always slowly add the acid to water while stirring the mixture

heat of the solution highly increases the temperature of the solution and causes it to boil and splatter

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Properties of Chemicals

Nitric acid

(HNO

3)Strong oxidizing agentReacts more rapidly than sulfuric acidDilute nitric acid causes the exposed skin to become yellowish brown if not washed off completely

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Properties of Chemicals

Phosphoric acid

(H

3PO4) is a weak acidHighly viscous when concentratedStrong dehydrating agentWhen diluting the acid, always add the acid to water slowly while stirringdilute solutions taste sweet (used as a sweetner in soft drinks)

Do not taste or swallow the phosphoric acid that is available in the laboratory

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Properties of Chemicals

Perchloric acid

(HClO

4):Very powerful oxidizing agent, particularly at elevated temperaturesReacts explosively with organic compounds and other reducing agentsMust be used only in a specially constructed water-wash-down laboratory hoods that has been designated to be used only for this purpose

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Properties of Chemicals

Never work with perchloric acid on laboratory benches made of combustible material (e.g. Wood)

Keep perchloric acid bottles on glass or ceramic secondary containment trays with edges that are high enough to hold all the acid if the bottle breaks

Always digest organic matter with nitric acid before adding perchloric acidDo not mix sulfuric or phosphoric acid with perchloric acid

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Properties of Chemicals

Picric Acid

Dry acid is highly explosive

To be used only when necessaryPicric acid contents should be moistened before opening the bottle (explosive peroxides may have formed in the cap threads)Immerse old picric acid bottles in water and slowly twist the cap to allow water to dissolve any crystals, then add water to moisturize the picric acid

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Properties of Chemicals

Bases:

Aalkali metal hydroxides and aqueous solutions of ammonia are the most common bases

Na and K hydroxides are strong bases and very destructive to the skin and the eyesBe cautious when preparing concentrated solutions of these bases (high temperature are produced that cause boiling and splattering)Vapors of aqueous ammonia solutions are irritating and toxic

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Properties of Chemicals

Examples of Toxic Materials

Halogens:

toxic oxidizing agents, especially FCl is a strong oxidizing agentBr is a corrosive volatile liquid that causes serious burns on skin contact (lachrymator (tear gas) and should be used in a fume hood)

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Properties of Chemicals

Mercury

Hg evaporates easily and fill the air with toxic vapors

Its vapor is a cumulative poisonSpilled Hg should be immediately and thoroughly cleaned up using an special apparatusinform your instructor in case of a Hg spillSpilled Hg can be made nonvolatile by amalgamation with zinc dust or tin powder

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Properties of Chemicals

Strong bases

all are corrosive and can cause serious, destructive chemical burns, including blindness

Strong bases are insidious (no immediate pain even with concentrated solution, pain starts after severe damage)saturated solutions (even dilute) of strong bases, such as Ca(OH)2, also are extremely corrosive

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Properties of Chemicals

Formaldehyde

A colorless, water-soluble, pungent, and irritating gas

Available as an aqueous solution of formaldehyde at concentrations varying from 37 to 56% (formalin)Inhalation of formaldehyde vapors results in severe irritation of the upper respiratory tract and lead to edema (accumulation of body fluids under skin)

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Properties of Chemicals

Do not breathe formaldehyde vapors (may cause cancer, results in severe eye irritation)

Avoid contact of formaldehyde solution with skin (causes sensitization and allergy)

Formaldehyde should be used and handled only in a designated laboratory fume hood

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Properties of Chemicals

Cyanides and nitriles

Rapidly acting toxic substances via all routes

Overexposures can be fatalA few inhalations of HCN can cause mental deterioration; a few more can be fatal Some metal cyanides form HCN in aqueous solutions or in the presence of acid

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Properties of Chemicals

Before working with cyanides, you must have amyl nitrite pearls handy as a first aid antidote

Names of

physicians who can treat overexposures to cyanide and can administer sodium nitrite and sodium thiosulfate solutions should also be available

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Properties of Chemicals

Organic Peroxides and Peroxide Formers

Organic peroxides are usually unstable and extremely flammable

Peroxides are among the most dangerous chemicals normally handled in laboratoriesExtremely sensitivite to shock, sparks, heat, friction, and strong oxidizing and reducing agents and therefore explode violentlyPeroxides have a specific half-life (rate of decomposition)

ETHER

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Properties of Chemicals

Never open a container if you suspect that it has peroxide (may explode)

The following compounds form peroxides

AldehydesEthers (e.g. cyclic ethers, ethers derived from primary and secondary alcohols)Compounds containing benzylic hydrogen atoms (e.g. isopropyl benzene)Compounds containing the allylic (CH2

= CHCH

2

–) structure, including most alkenes

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Properties of Chemicals

Ketones, especially cyclic ketones

Vinyl and vinylidene compounds (e.g., vinyl acetate and vinylidene chloride)

Containers of ethyl or isopropyl ether must be labled with the date they are received, they must be destroyed within 3 months after receiptNever distill an ether unless it is known for certain to be free of peroxides, and even then do not distill to dryness

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Properties of Chemicals

Examples of chemicals that can form dangerous concentrations of peroxides when exposed to air

Cyclohexene

CycloocteneDecalin (decahydronaphthalene)p-DioxaneEthyl etherIsopropyl etherTetrahydrofuran (THF)

Tetralin (tetrahydronaphthalene

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