CorrosIves Can Be Inhaled
• Some corrosive chemicals pose hazards via the inhalation route in gaseous, fume, mist, or powder forms that can cause damage to mucous membranes or lung tissue. Although they are not common in pharmacy education labs, it is good to know the hazards of them.
These gases can be inhaled and can cause severe damage to skin, eyes, nose, and the sensitive lining of the lungs that in some cases can lead to delayed fluid buildup in the lungs called pulmonary edema—a dangerous medical condition that can be fatal.
• Cu(s) + 4HNO3(aq) →Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l )
• There are two corrosive substances to be aware of here: a reactant, strong nitric acid, and a product, gaseous nitrogen dioxide. This red gas is a strong oxidizing agent and will react with water (moisture) in your lungs to produce nitric acid. Brief exposure to as little as 250 ppm will cause frothy sputum, difficulty breathing, and increased respiration and heart rates. And these symptoms may persist for 2–3 weeks. (In nonlab settings, NO2 is a main component of smog in urban areas although concentrations are closer to 0.1 ppm. The main source of NO2 is automobile engine exhaust. Catalytic converters use elemental rhodium to reduce the NO2 to N2) Any reaction producing NO2 should be conducted in a chemical hood.
CorrosIves Can Be Inhaled
• NH3(aq) + H2O(l) NH4+ (aq) + OH−(aq)
• And the dissolved ammonia is in equilibrium with the vapor over the surface of the liquid:
• NH3(aq) NH3(g)
• Henry’s law describes the solubility of a gas in water as a function of the partial pressure of the gas
• over the surface of the solution. It is described by the equation
• S = kHP
• where S is the solubility of gas (as molarity), P is the partial pressure of the gas over the surface of the solution, and kH is the Henry’s law constant for a particular gas.
• We can use Henry’s law to calculate the vapor pressure of ammonia over the surface of solutions of ammonium hydroxide. The Henry’s law constant for ammonia is 58 atm/M. Let’s assume that we
• are using 6 M NH4OH: P = S /kH
• = (6 M)/(58 M/atm)
• = 0.1 atm
• A concentration of 0.1 atm is equal to 100,000 ppm. The IDLH (immediately dangerous to life or health) value for ammonia is 300 ppm. So if we take a good strong whiff of the vapor over the surface of 6 M ammonia, we are smelling ammonia at over 300 times the IDLH value! But one whiff is not 30 minutes. Alternatively, we can look at the LClo for mammals, which is 5000 ppm for 5 minutes. This is the lowest concentration known to cause death. So, if we are breathing 100,000 ppm we are
breathing 20 times the concentration that is lethal in 5 minutes for mammals. All of this should convince you to use 6 M NH3 (and other high-concentration ammonia/ ammonium hydroxide solutions) in a chemical hood! Even though it is a solution, the vapor over the surface of this solution is quite harmful.
OxIdIzIng Agents
• Nitric acid is probably the oxidizing agent that you are most likely to use—and we’ve already discussed this in the consideration of strong acids! So, it can be dangerous in two fashions. Its corrosive effect is due mainly to its oxidizing power, in fact, more so than its capability as a strong acid. In fact, nitrate salts such as KNO3 and NH4NO3 are also good oxidizing agents. It’s the nitrate that is the oxidizing species.
• Hydrogen peroxide is another common oxidizing agent. It is also a fairly common household chemical that can be used for disinfecting wounds (3%) or decolorizing hair (15%). Laboratory solutions can be as high as 30%, which is extremely corrosive. The by-product of this oxidizing agent is water, which makes it convenient to use. Solutions with a concentration of > 8% are considered corrosive.
• Some laboratory titrations are conducted using potassium permanganate (KMnO4) since it is a strong oxidizing agent and the disappearance of the purple permanganate acts as an endpoint indicator. Dilute solutions that you are likely to use are only mildly irritating to the skin but
high concentrations and the solid salts are very corrosive.
• The bottom line here is that any good oxidizing agent will likely be able to oxidize you, too!
Your skin and eyes will become the targets of these oxidizing agents unless appropriate precautions are taken.
FLAMMABLES
• Flammable chemicals are chemicals that easily ignite and rapidly burn, releasing large amounts of energy, mostly in the form of heat. (Sometimes you see the term
inflammable—it is a synonym of flammable.) Once ignited, they continue to burn as a self-sustaining reaction until the chemical is consumed or it is extinguished. Indeed, they have a passion for burning, and they come in all forms: gases, liquids, and even solids.
• Combustible chemicals become flammable if they are heated so that they give off
sufficient vapors to be easily ignited. While combustibles are more difficult to ignite, once ignited they also readily burn.
• The boiling point of a flammable liquid is usually relatively low.
• The flash point of a chemical is the lowest temperature at which its vapors near the liquid surface can be ignited under controlled conditions. For a liquid this is the lowest
temperature at which vapors,above its surface mixing with air, can form an ignitable
mixture. The autoignition temperature is the temperature at which a flammable chemical ignites in air spontaneously under controlled conditions. The lower the autoignition
temperature, the greater the potential risk for a fire. Autoignition temperatures are generally quite high,
FLAMMABLES
• Each chemical has a range of concentrations of its vapors called flammability limits within which a fire or explosion can occur, while fires will not occur below or above those limits.
The lower explosive limit (LEL), sometimes called the lower flammability limit (LFL), is the lowest concentration of vapor in air, expressed in percent by volume, at which a fire can be started resulting in an explosion, when a source of ignition is present. Below the LEL, the concentration of the vapor is insufficient to support burning. The upper explosive limit (UEL), sometimes called the upper flammability limit (UFL), is the highest concentration of vapor in air expressed in percent by volume, at which a fire will be propagated. Above this limit the concentration of the vapor is too high to support burning. These limits become wider as temperatures are increased and as oxygen content is increased. The result of
these variations in LEL and UEL is that flammability limits are not very useful. For example, when a flammable liquid is spilled its LEL is quickly achieved as the broad surface allows large amounts of chemical to vaporize, and if this occurs within the presence of an ignition source a fire or explosion can occur
FLAMMABLES
• Fire Hazard Rating Systems
• The United Nation’s Globally Harmonized System (GHS) defines
flammable and combustible liquids in terms of measurable chemical properties. This hazard rating system uses a 1 for the highest level of flammability hazard and a 4 for the lowest level of flammability
hazard.
Properties of Flammable and Combustible Liquids as Defined by the Globally Harmonized System for Classification and Labelling of Chemicals
FLAMMABLES
• Laws require that flammable chemicals be labeled as such. The GHS has devised a hazard class (HC) rating system that
includes flammables and this system can help you recognize the relative flammable hazard of a chemical. These ratings range from HC 1 to HC 4 with HC 1 being
extremely flammable and HC 4 being combustible liquids.
• Mostly, flammability is strongly related to volatility but there are also nonflammable volatile chemicals. Molecular structure affects flammability.
Why Are Fires So Dangerous?
There are three main effects from a fire that are dangerous: heat released, toxic by-products from the combustion, and oxygen consumed.
INCOMPATIB LES
• Incompatible chemicals are combinations of substances,
usually in concentrated form, that react with each other to produce very exothermic reactions that can be violent and explosive and/or can release toxic
substances, usually as gases.
INCOMPATIBL
ES
• Water-reacting compounds• We ordinarily consider water to be fairly nonreactive. Water-reactives are chemicals that react violentlywith water, releasing large amounts of heat and sometimes flammable gases or toxic gases, often resulting in fires or explosions
Examples of Water-Reactive Classes of Compounds
Strong Oxidants and Reductants
These compounds are imcompatible with many others as they react with them by producing high amount of energy.
The most commons are nitric acid and nitrate, perchloric acid, permanganate and hydrogen peroxide.
