Hazardous Materials
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Ch.8pg270-290.pdf
CHAPTER
Courtesy of Bulk Transportation, Inc., Walnut, California.
i3flh;iMfA acid, p. 272 acidic. p. 274
8 Chemistry of Some Corrosive Materials
oxidizing acid, p. 274 pH, p. 274 pickling, p. 278
- acidic anhydride (nonmetallic oxide), p. 277
concentrated acid, p. 274 corrosive material, p. 271 corrosive substance, p. 271 diluted acid, p. 274 hydronium ion, p. 272 hypocalcemia, p. 292 mineral acid, p. 273 nonoxidizing acid, p. 274
RCRA corrosivity characteristic, p. 300 salt, p . 276
alkaline, p . 274 anhydride, p. 277 aqua regia, p. 285 base,p. 272 basic (caustic), p. 274 basic anhydride (metallic oxide), p. 277
oleum (fuming sulfuric acid), p. 282 organic acid (carboxylic acid), p. 274
slaking, p. 299 strong acid, p. 273 strong base, p. 273 weak acid, p. 273 weak base, p. 273
i•1=!ii3ir,tA Associate the physical and health hazards of the corrosive materials noted in this chapter with the information provided by their hazard diamonds and GHS pictograms. Identify the primary industries that use the corrosive materials noted in this chapter. Identify the concentrated acids that vaporize at room temperature and cause ill effects when inhaled. Identify the labels, markings, and placards that DOT requires on packaging of cor- rosive materials and the transport vehicles used for their shipment. Identify the response actions to be executed when corrosive materials are released from their packaging into the environment.
270
The most common examples of · · · ll 'd d b corrosive materials are substances known chem1-ca as ac1 s an ases T . . . • Y . d · hey are compounds capable of causmg 1rritat1on, burns, or more serious amage to tissu d d' h · · · h b
. e, epen mg on t e1r strength. Their umque prop- ·es and t e manner y which acids d b d • · · ertl an ases corro e matter are the prmc1pal subiects
of this chapter.
s.1 THE NATURE OF CORROSIVITV Corrosivity is a chemical property exhibited by certain substances. In everyday practice, we sa~ that these substances "ea~ into" and destroy the quality of metals, minerals, and body tissues. Government regulat10ns, however, provide more specificity as the following definitions demonstrate: '
CPSC defines _a corrosive substance as any consumer product that destroys liv- ing tissue such as _skm or eyes by chemical action . At 16 C.F.R. §1500.41, a product is considered corrosive to the skin if, when tested on the intact skin of the albino rabbit the structure of the tissue at the site of contact is destroyed or changed irreversibly i~ 24 hours or less.
DOT defines a corrosive material as a liquid or solid that causes full-thickness destruction of human skin at the site of contact within a specified period, or a liquid that chemically reacts with steel or aluminum surfaces at a rate exceeding 0.25 inches/year (6.25 mm/y) at a test temperature of 130°F (54°C) when measured in accordance with prescribed testing procedures.
During emergency response actions, corrosive materials often are encountered in non- bulk containers like lined steel drums (1A1 or 1A2), plastic drums (1H1 or 1H2), and plastic carboys (3H1 or 3H2). As a minimum, OSHA requires manufacturers, distribu- tors, and importers of chemical products to post the corrosion-symbol pictogram on the labels of corrosive materials, along with an appropriate hazard signal word and hazard and precautionary statements.
Corrosive materials are transported in bulk in rail tankcars or cargo tanks. Both the DOT-111 rail tankcar and MC-312 cargo tank are low-pressure [<75 psi (517 kPa)] transport vessels manufactured from steel and generally lined with rubber. Their design and construction features are published at 49 C.F.R. § § 173.242 and 178.343, respec- tively. To provide an element of safety, the MC-312 cargo tank is equipped with stiffening rings and rollover protection. . .
When carriers transport 1001 pounds (454 kg) or more of a corrosive material, DOT requires them to display CORROSIVE placards on the bulk packaging used for shipment. When more than one corrosive material is transported in a compartmented tankcar or c~rgo tank, DOT requires carriers to placard each compartment separately as shown in Figure 8.1. to :When carriers transport corrosive materials by highway or rail, DOT requires them
display the relevant identification number on orange panels or across the center area ofhthe CORROSIVE placards or white square-on-point diamonds. For example, :/n sod~um hydroxide (Section 8.14), a corrosive material, ~s tran~po_rted ?~ h1?h- n Y or rail, carriers may use any of the following means to display its identif1cat10n Ulllber 1824:
corrosive substance For purposes of
CPSC regulations, any substance that causes the destruction of living tissue by chemical action
corrosive material For purposes of DOT regulations, a liquid or solid that causes full- thickness destruction of human skin at the site of contact within a specified period; or a liquid that chemically reacts with steel or aluminum surfaces at a rate exceeding 0.25 inches/year (6.25 mm/y) at a test temperature of 130°F (54°C) when measured in accordance with prescribed testing procedures
L Chapter 8 Chemistry of Some Corrosive Materials 271
acid A compound that forms hydrated hydro- gen ions, W(aq), when dissolved in water
hydronium ion The simplest hydrated hydrogen ion,denoted as H(H 2O}', or H3o•
A hydroxide of the alkali and alkaline earth metals and certain other substances whose aqueous solutions have a pH greater than 7
. FIGURE 8 .1 DOT requires the front and rear ends of a compartmented cargo tank to be placarded in same sequence as the compartments are being transported . This three-compartment cargo tank is placarded to transport caustic soda solution, for- mic acid, and an "other regulated liquid sub- stance ." The latter is a class 9 hazardous material, whereas caustic soda solution and formic acid are class 8 corrosive materials. To comply with DOT marking requirements, the carrier has posted identification numbers across the center of each placard . (Courtesy of Bulk Transportation, Inc., Walnut, California.)
8.2 THE NATURE OF ACIDS AND BASES Several theories have been proposed to account for the properties of acids and bases, but for simplicity's sake, we use only one of them in this text. In 1887, Swedish chemist Svante Arrhenius first advocated a theory that has been modernized here to reflect current scientific knowledge. Arrhenius proposed that an acid is any substance that generates hydrogen ions (H•) when dissolved in water. Hydrogen ions are hydrogen atoms that have been stripped of their electrons. A single hydrogen ion is the same as the nucleus of a hydrogen atom, or a single proton.
Today, chemists know that free hydrogen ions cannot exist alone in aqueous solution due to their high charge density. Instead, they rapidly become "solvated"; that is, they bond loosely to water molecules. These solvated hydrogen ions are very complex in the manner in which they interact with water. The simplest ion is H(H20)+, or H3 0•; it is called the hydronium ion. We collectively represent here all solvated hydrogen ions by the notation H•(aq).
For instance, when hydrogen chloride dissolves in water, solvated hydrogen ions and chloride ions are generated.
HCl(aq) H +(aq) + c 1-(aq) Hydrogen chlori de Hy drogen ion Chloride ion
This solution of hydrogen chloride in water is called hydrochloric acid. Its chemical formula is HCl(aq ).
Arrhenius further proposed that a base is a substance that produces hydroxide io~s (OH-) when it is dissolved in water. For example, when sodium hydroxide dissolves ill water, solvated sodium and hydroxide ions are generated. We represent them as Na• (aq ) and OH-(aq ), respectively.
NaOH(aq) Na +(aq) + OH-(aq) Sodiu m hydrox ide Sodium ion Hyd rox ide ion
The solution of sodium hydroxide in water is represented as N aOH(aq ).
272 Chapter 8 Chemistry of Some Corrosive Materials
s.2-A STRONG AND WEAK ACIDS AND BASES I is the ability of acids and bases to form ions in water that gives rise to their corrosive nrarure. The relative strength of an aci~ or base refers to the tendency of an individ~al substance to form hydrated hydrogen ions and hydroxide ions, respectively, when dis-
. so Acids and bases that yield a relatively high concentration in water of hydrated hydro- gen and hydroxide _ions_ a~e called strong acids and strong bases, respectively. ~or jnsrance, hydrochl~nc_ aci~ is an example of a strong acid, because the hydrogen chlonde fmost completely 10mzes m water. Likewise, sodium hydroxide is an example of a strong
~ase, because it almost completely ionizes in water. In contrast, some substances essentially retain their unit formulas when they are dis-
solved in water. Such substances yield relatively low concentrations of hydrogen or hydroxide ions and ar~ called we~k a~ids and weak bases, respectively. Acetic acid i~ a_n example of a weak acid, because It pnmarily exists as molecules of acetic acid when 1t 1s dissolved in water, although some hydrogen and acetate ions are also produced. Ammo- nium hydroxide is an example of a weak base. When ammonia is dissolved in water, it continues to exist primarily as molecular ammonia and does not appreciably from ammo- nium and hydroxide ions.
Each acid in the group listed in Table 8.1 is ranked as a strong or a weak acid. Phosphoric acid is regarded as a moderately strong acid, whereas the acids above and below phosphoric acid in this listing are considered strong acids and weak acids, respectively.
8.2-B MINERAL ACIDS AND ORGANIC ACIDS Acids may be classified as either mineral acids or organic acids. Mineral acids consist of molecules having atoms of hydrogen; an identifying nonmetal like chlorine, sulfur, or phosphorus; and sometimes oxygen. Mineral acids most likely are so named because they were initially produced from minerals existing in naturally occurring ores.
TABLE 8.1 Relative Strengths of Some Common Acids in Water
NAME OF ACID CHEMICAL FORMULA
Perchloric acid HCI04(aq)
Sulfuric acid H2S04'aq)
Hydrochloric acid HCl(aq)
Nitric acid HN03(aq)
Phosphoric acid H3P04(aq) Nitrous acid HN02(aq)
Hydrofluoric acid HF(aq) Acetic acid CH3COOH(aq) Carbonic acida C02(aq) Hydrocyanic acid HCN(aq) Boric acid H3B03(aq)
'The chemical form I f b . 'd sometimes appears in the literature as H2COJ{aq). An acid having this che . u a o car onic ac1 h 1 1 f I f b · 'd · m1cal compo 'ti h b Isolated or identified. The c em ca ormu a o car on1c ac1 1s co s1 on, owever has never een d . rrectly denot d C ' . h d' th fact that carbonic acid has never been dlscovere , solutions of carbon d e as 0 2(a q) . Notw1t stan rng e
loxlde In water are acidic in nature.
strong acid Any acid that predominantly forms hydrated hydro- gen ions when dis- solved in water
strong base Any base that predominantly forms hydrated hydrox- ide ions when dissolved in water
weak acid Any acid that predominantly retains its molecular identity when dissolved in water
weak base Any base that predominantly retains its unit identity when dissolved in water
mineral acid Any inorganic acid, chiefly hydrochloric acid, sulfuric acid, nitric acid, perchloric acid, phosphoric acid, and hydrofluoric acid
Chapter 8 Chemistry of Some Corrosive Materials 273
organic acid (carboxylic acid) An organic compound containing one or more of the group of atoms
0 II
-c \ OH
oxidizing acid Any acid capable of reacting as an oxidizing agent
nonoxidizing acid Any acid incapable of reacting as an oxidizing agent
concentrated acid The term routinely applied to the commercially available form of an acid containing the greatest concentration of the substance
diluted acid Any form of an acid that has been produced by mix- ing a concentrated acid with water
pH A numerical scale from O to 14 used to quantify the acidity of alkalinity of a solution with neutrality indi- cated as 7
acidic The property of aqueous solutions that have a pH ranging from O to 7; the prop- erty of any substance that corrodes steel or destroys tissue at the site of contact
basic (caustic) The property of aqueous solutions that have a pH rang ing from 8 to 14
alkaline Basic, as opposed to acidic; an aqueous solution or other liquid whose pH is greater than 7
The mineral acids are distinguished from organic acids, or carboxylic acids stances whose molecules usually possess carbon, hydrogen, and oxygen atoms ortl sub. organic acids have molecular structures that contain the following group of atoms: y, All
0 II - c \ OH, or - COOH.
Acetic acid is the only organic acid noted in this chapter, but in Section 13.6, we will v· . other organic acids. Collectively, they are weak acids. lSJt
8.2-C OXIDIZING AND NONOXIDIZING ACIDS An acid chemically reacts as either an oxidizing acid or a nonoxidizing acid. An oxidizing acid participates in chemical reactions as an oxidizing agent. A nonoxidizing acid participates in a chemical reaction by some means other than oxidation.
Hot, concentrated sulfuric acid, nitric acid, and perchloric acid are oxidizing acids, but hydrochloric acid, hydrofluoric acid, phosphoric acid, and acetic acid are nonoxidizing acids. The degree to which the oxidizing acids corrode depends on how powerfully they participate as oxidizing agents. We note this characteristic when we examine their individual properties.
8 .2-D CONCENTRATED AND DILUTED ACIDS Chemists often refer to an acid as either diluted or concentrated. When they refer to a concentrated acid, chemists generally mean the commercially available acid that has the greatest concentration. When referring to a diluted acid, they mean a solution produced by adding water to the concentrated acid.
This is not meant to imply that water is absent from a concentrated acid. A concentrated acid may actually contain some amount of water. For example, concentrated hydrochloric acid consists of approximately 36% to 38% hydrogen chloride by mass in water; 62% to 64 % of the solution is water. Diluted hydrochloric acid is any solution that results when addi- tional water is added to this concentrated acid. Although concentrated hydrochloric acid is a corrosive material, diluted hydrochloric acid may or may not exhibit corrosiveness depending on its strength. When highly diluted with water, all acids lose their corrosive charactet
8.3 THE pH SCALE The pH is a number ranging from 0 to 14 that denotes the acidity or alkalinity of an aqueous solution. Aqueous solutions of substances that have a pH less than 7 are said to be acidic. Let's consider a simple example. In pure water, there is a very small hydrogen ion concentra· tion derived by the dissociation of the water molecules. This is represented as follows:
H20(/) tt+(aq) + OH-(aq) Water Hydrogen ion Hydroxide ion
When the hydrogen ion concentration in pure water is determined experimentally, we find that it is only 0.0000001 (or 10-7) moles/liter. Instead of writing all these zeros, we expret this concentration by indicating that the pH equals 7; that is, the pH is the de?ree_ of t0~ negative exponent. When the hydrogen ion concentration of an aqueous solut10n
15 O. (or 10-2) moles/liter, the pH of the solution equals 2. .
Aqueous solutions having a pH greater than 7 are referred to as basic, cau5tic,8°; alkaline. Because water is neither acidic nor basic, the pH of pure water is 7. Table · lists the pH values of some common solutions and mixtures. .
A unit change in a pH value represents a 10-fold difference in the hydrogen ion con;5 tration of a solution, and a difference of two pH units represents a 100-fold difference.
274 Chapter 8 Chemistry of Some Corrosive Materials
d
TABLE 8.2
Limewater, Ca(OH)i Household ammonia
Milk of magnesia
Blood-------1
14
1 13 12
11 Increasingly 10 basic
9
8 Pure water----....J..._7------ -- --- ---- ----- --Neutral----------- -Tap water------J
6 Coffee-------1-5
Wine--- - --~ Vinegar------ Lemon juice•-- ---1 Gastric juice------,
4
3
2
0
Increasingly acidic
j means that the hydrogen ion concentration of an aqueous solution having a pH of 4 is 100 times greater than the hydrogen ion concentration of a solution having a pH of 6; and it is 1000 times greater than one having a pH equal of 7. In everyday practice, we say that a solu- tion having a pH of 4 is 100 times more acidic than a solution having a pH of 6 and 1000 times more acidic than a solution having a pH of 7. Also, a solution with a pH of 8 is 10 times as alkaline as one with a pH of 7; a solution having a pH of 9 is 10 times as alkaline as one having a pH of 8 and 100 times as alkaline as one having a pH of 7; and so on.
The pH is frequently determined by means of an electrometric apparatus called a pH meter. The pH meter illustrated in Figure 8.2 is a voltage-measuring device that is connected
/
FIGURE 8 .2 The pH of an aqueous solution is determined by using a pH meter. The user immerses the electrodes in a sample of the solu- tion, whose pH is read on the display monitor. (Courtesy of Mettler-Toledo International, Inc., Columbus, Ohio. )
Chapter 8 Chemistry of Some Corrosive Materials 275
A compound in which the hydrogen ion from an acid has been substituted with a metallic ion
y to an electrode whose tip is immersed in a solution. The pH of the solution is r dil mined by simply reading a display monitor. ea Y deter,
8 .4 PROPERTIES OF ACIDS AND BASES All acids are associated with certain common properties. They taste sour; the indicator dyes to change to identifiable colors; and they react with bases to fo; cause and water. In contrast, bases taste bitter; they feel slippery; they also cause the co7 salts indicator dyes to change to identifiable colors; and they react with acids to for:::~! and water. ts . Acids a_nd bases_ can be readily diff~rentiated froi:n ~ne another b! the colors the impart to pieces of litmus paper. Litmus 1s a common md1cator dye derived from cert .Y lichens, any of a group of mosslike plants. A solution of litmus is used to impregn: tn strips of paper that are subsequently dried. Individual strips are moistened with an aqu:~ ous solution of an acid or a base. Acids turn the litmus paper red, and bases turn the lit- mus paper blue.
When acids and bases chemically interact, they neutralize each other. An example of a neutralization reaction is represented by the following equation:
HCI(aq) + NaOH(aq) NaCl(aq) + H20 (l) Hydrochloric acid Sodium hydroxide Sodium chloride Water
The compou-nd whose formula is listed to the immediate right of the arrow is called a salt. Any compound in which the hydrogen in an acid has been replaced by a metallic ion is a salt. Na Cl is the chemical formula of sodium chloride, which we commonly know as ordi- nary table salt. It has properties that are dissimilar from those of both hydrochloric acid and sodium hydroxide.
8.5 THE ANHYDRIDES OF ACIDS AND BASES When a metallic or nonmetallic element combines with oxygen, the compounds produced are metallic oxides and nonmetallic oxides, respectively. Sodium and calcium are two examples of metals that burn in oxygen to form their corresponding metallic oxides.
4Na(s) + 02(g) 2Na20(s) Sodium Oxygen Sodium oxide
2Ca(s) + 02(g) -----+ 2CaO(s) Calcium Oxygen Calcium oxide
Sulfur and phosphorus are two ~xamples of nonmetals that burn in oxygen to form their corresponding nonmetallic oxides.
Ss(/) + 80 2(g) -----+ 8S02(g) Sulfur Oxygen S ulfur d ioxide
Phosphorus O xygen Tetrap hospho ru s hexoxide
A metallic oxide reacts with water to produce a base. These combination reactions are denoted as follows:
Na20(s) + H20 (/) -----+ 2NaOH(aq) Sodium ox ide Water Sodium hydroxide
CaO(s) + H20(/) -----+ Ca(OH)i(aq) Calcium oxi de Water Calc ium hydro xide
Chapter 8 Chemistry of Some Corrosive Materials
TABLE 8.3 Acidic and Basic Anhydrides
CHEMICAL CHEMICAL ANHYDRIDE FORMULA ACID/BASE FORMULA Dinitrogen trioxide N203 (g ) Nitrous acid HN0 2(aq) Din itrogen pentoxide N20 5 (g) Nitric acid HN03(aq) sulfur dioxide S0 2(g) Sulfurous acid H2S0 3(aq) sulfur trioxide S03(g) Sulfuric acid H2S 0 4(aq) Tetraphosphorus hexoxide P405(s) Phosphorous acid H3P0 3(aq) Tetraphosphorus decoxide P40 1o(s) Phosphoric acid H3P04(aq) calcium oxide CaO(s) Calcium hydroxide Ca(OH)z(aq) Magnesium oxide MgO (s) Magnesi um hydroxide Mg(OH)z(aq) Potassium oxide K2 0 (s) Potassium hydroxide KOH(aq ) sodium oxide Na20 (s) Sodium hydroxide Na OH(aq)
A nonmetallic oxide reacts with water to produce an acid . These combination reactions are represented by the following equations:
S 0 2(g) + H20(l) - H 2S03(aq) Sul fu r di ox ide Wate r Sul fu rous acid
Te traphos phoru s hexox ide Water Phosphoro us aci d
The word anhydride refers to a substance from which the elements of water have been extracted. It is either a metallic or a nonmetallic oxide. A metallic oxide that com- bines with water to produce a base is called a basic anhydride, and a nonmetallic oxide that combines with water to produce an acid is called an acidic anhydride. Sodium oxide and calcium oxide are examples of basic anhydrides, and sulfur dioxide and tetraphos- phorus hexoxide are examples of acidic anhydrides. Some common acids and bases and their respective acidic and basic anhydrides are listed in Table 8.3.
Any metallic or nonmetallic oxide
basic anhydride Any metallic oxide that chemically combines with water to produce a base
acidic anhydride Any nonmetallic oxide that chemically combines with water to produce an acid
SOLVED EXERCISE 8.1
Write equations for th e followin g chemical phenomena :
(a) Bubbles of hydrogen are generate d wh en small chu nks of metallic calc ium are dropped into an aqueous solution of hydrochloric acid .
(b) A surface coating of zinc oxide is rem oved by an aq ueous solution of sulfuric acid . (c) Bubbles of carbon dioxide are generated w hen potassium carbonate is mixed into an aqueous solution
of phosphoric acid.
Solution: The phenomena in (a), (bl, and (cl are rep re sentative of t he chemica l reactions of ac ids w ith metals, metallic oxides, and metallic carbonates, respective ly.
(a) Acids react with common metal s other than coppe r, sil ver, gold, and mercury to produce hydrogen and a salt of the metal . Conseque ntly, metallic ca lcium reacts w ith hydrochloric acid to produce hydrogen and calcium chloride according to the fo ll owing equation :
Ca(s) + 2HCl(aq) -----> CaCl2(aq) + H2(g) Calcium Hydrochloric acid Calcium chlo ride Hydrogen
Chapter 8 Chemistry of Some Corrosive Materials 277
/'
I I
I
I I I
pickling The combina- tion of chemical reac- tions associated with removing impurities from the surfaces of metals by immersing them in an acid bath
(b) Acids react wit h meta llic oxi des to prod uce w ater an d a salt of the metal. Consequently, zinc OXid acts with sulfuric aci d to produce zi nc sulfate an d w at er. ere.
ZnO(s) + H2S0 4(aq) ---> ZnS04(a q) + H20(/) Zi nc oxide Sulfuric acid Zinc sul fa te Water
(c) Acids rea ct with meta llic ca rbonates to pro duce carbon dioxide, water, and a salt of the metal C d h h . 'd d . on sequently, t he reaction bet ween potassi um carbonate an P osp one aci pro uces carbon dioxid;
water, and potassium phosphate. '
3K2C03(S) + 2H3P04(aq) ---> 3C Oz(g) + 3 Hz 0 (/) + 2 K3 P0 4(aq) Potassium carbonate Phosphoric acid Ca rbon dioxi de Water Potassium ph osph ate
8.6 ACIDS AND BASES AS CORROSIVE MATERIALS Acids act as corrosive materials by reacting with metals, metalli~ oxid~s, metallic carbon. ates, and skin tissue. Bases act as corrosive materials by reactmg with metals and skin tissue. We consider these phenomena separately.
8 .6-A REACTIONS OF ACIDS AND METALS Diluted acids react with all the commonly encountered metals ~ther than copper, silver, gold, and mercury. These are simple displacement react10ns that produce hydrogen and a salt of the metal. Two examples of such reactions are illustrated by the following equations:
Mg(s) + 2HCl(aq) - MgClz(aq) + Hz(g) Magnesium Hydrochloric acid Magnesium chloride Hydrogen
2Al(s) + 3H2S0 4(aq) - Al2(S04))(a q) + 3Hz(g) Aluminum Sulfuric acid Aluminum sul fate Hydrogen
Because acids and metals are chemically incompatible, it is unsafe to store acids in metal containers. This is why nonbulk quantities of acids are usually stored in glass or plastic containers. When they are stored in metal drums or pails, the containers must be rubber-lined.
8 .6-8 REACTIONS OF ACIDS AND METALLIC OXIDES Acids react with metallic oxides to form a salt of the metal and water. Examples of this type of double-displacement reaction are illustrated by the following equations:
FeO(s) + 2HCl(aq) - FeC12(aq) + H20 (l) lron(ll) ox id e Hydrochl oric acid Iron(II) chlo rid e Water
Aluminum oxide Nitric acid Al uminu m nit rate Wate r
An acid is sometimes beneficially used to remove metallic oxides and other impurities from the surface of metals. When used in this fashion, the acid is commonly called pickle liquor, and t?e ass?ciated p?enomenon is called pickling. The steel industry uses lar;~ volumes of pickle hqu~r durmg_the _manu~acture of such products as wire, ro~, nu_cs, :nd bolts. The common acids used m pickle liquors are sulfuric acid, hydrochloric acid, phosphoric acid.
278 Chapter 8 Chemistry of Some Corrosive Materials
S,6-C REACTIONS OF ACIDS AND METALLIC CARBONATES ·ds react with metallic carbonates to produce carbon dioxide water and a salt of the Ac1 f h . . , ,
rnetal. Examples O t ese reactions are illustrated by the following equations: CaC03(s) + 2HCl(aq) - CaC J2(aq) + C0 2(g) + H 20(l) Calcium carb onme Hydroc hloric acid
Calcium chl oride Carbon diox ide Water
Z inc carbonate S ul furic aci d Zinc su lfate Carbon dioxide Water
s.G-D REACTIONS OF ACIDS WITH SKIN TISSUE The nature of the corrosiv~ effect caused by prolonged exposure of skin tissue to an acid depends on the concentration of the acid. When the skin contacts a diluted acid, the site of contact may appear only reddened, whereas exposure to a concentrated acid for the same duration could cause the ~kin to blister. In the worst incidents, prolonged exposure of the skin to a c_oncentrated acid causes irreversible tissue damage and permanent disfig- urement at the site of co_ntact. In either situation, the skin tissue is said to be "burned," because its appearance visually resembles a thermal burn.
s.6-E REACTIONS OF BASES AND METALS Three common metals react with the concentrated solutions of strong bases, namely, alu- minum, zinc, and lead. During the chemical reactions, hydrogen and a complex com- pound of the metal are ~roduced. The following equations illustrate the chemical behavior of these three metals with a concentrated solution of sodium hydroxide:
2Al(s) + 6NaOH(aq) - 2Na3AI03(aq) + 3H2(g) Aluminum Sodium hydroxide Sodium aluminate Hydrogen Zn(s) + 2NaOH(aq) - Na2Zn02(aq) + H2(g ) Zinc Sod ium hydroxide Sodium zincate Hydrogen Pb(s) + 2NaOH(aq) - Na2Pb0 2(aq) + H2(g) Lead Sodium hydroxide Sodi um plumbite Hydrogen
The reaction between sodium hydroxide and aluminum is especially important when exam- ining the corrosive nature that strong bases exhibit with metals.
8.6-F REACTION OF BASES WITH SKIN TISSUE Aqueous solutions of bases corrode skin tissue in a fashion that is associated with the concentration of the base. When skin is exposed to a diluted solution, it appears reddened at the site of contact. Although wounds of this type heal rapidly, when the skin has been exposed to a more concentrated solution of the same base, it becomes sticky, soapy, and soft in texture. Prolonged exposure causes the development of deep wounds that turn black and leathery in texture and are very slow to heal. The tissue damage may be irre- versible and cause permanent disfigurement at the site of con_tact. . . ca Ex~o.su~e of the eyes to solutions of caustic substances ~s part1cularl_y worrisome. It 0 us~s. IUJunous changes in the structure of the cornea, ultimately leadmg to complete Pacification (clouding).
8 ·7 SULFURIC ACID
Sulfuric acid is . 1 'd h h mical formula is H 2S04• It is an odorless, col-Orie . a mmera ac1 w ose c e . 1 ss, oily liqu'd h • d • imately twice that of water. mpure or spent
sulfuric acid i's 61 avmgbal ek°:s1ty al pprAox 'ndustrial grade of sulfuric acid is sometimes rown to ac m co or. n 1
Sulfuric acid
Chapter 8 Chemistry of Some Corrosive Materials 279
FIGURE 8.3 This lead- acid storage battery con- tains a group of individual cells, each of which con- sists of a lead plate and a lead oxide plate immersed in an aqueous solution of sulfuric acid. The specific gravity of the sulfuric acid ranges from 1 .2 5 to 1 .30 and serves as an electrolyte .
TABLE 8.4 Physical Properties of Concentrated Sulfuric Acid
Melting point 50°F (10°()
Boiling point 640°F (338°C)
Specific gravity at 68°F (20°C) 1.84
Vapor density (air= 1) 2.8
Vapor pressure at 68°F (20°C) <0.001 mmHg
Solubility in water Infinitely soluble
encountered as a clear-to-brownish-colored liquid. The brown color reflects the p f h
. l . f res- ence o dissolved salts. Some of the important p ysICa properties o sulfuric acid noted in Table 8.4 . are
If we were to list chemical substances by the amounts produced and consumed annu- ally within the United States, we would find sulfuric acid near the top of these lists for the past five decades. In the United States alone, well over 40 million tons (36 million t) of sulfuric acid are produced annually. Sulfuric acid is so important commercially that its production and consumption rates have been used by economists to estimate the extent to which a country has industrialized.
The layperson is generally aware of sulfuric acid through its use as the electrolyte in the lead-acid storage battery shown in Figures 1.6 and 8.3. As previously noted in Section 7.2-G, this battery is the electrical source in virtually all motor vehicles. However, sulfuric acid has countless other uses. In the chemical industry alone, sulfuric acid is used to man- ufacture explosives, fertilizers, drugs, and dozens of other compounds-including other acids . Given its widespread usage, sulfuric acid has been called the workhorse of the industrial world. The popularity of its use implies that sulfuric acid is likely to be encoun- tered more frequently than other corrosive materials when responding to emergencies involving hazardous materials .
As first noted in Section 1.5-A, OSHA requires every manufacturer, distributor, and importer of a chemical substance to ensure that appropriate hazard warnings are pro· vided on their containers. For example, OSHA requires them to provide the GHS hazard information on the label shown in Figure 8.4 when the label is affixed to containers of concentrated sulfuric acid. The information written under the heading DANGER con· sists of GHS hazard and precautionary statements . The symbols required by WHMIS also are shown.
Positive terminal Negative terminal
Ventcaps - --- ---
Electrolyte solution Cell connectors - .W.::~ ~;S::~-l (dilute sulfuric acid)
Positive electrode -++---a¼-l-_...111 Protective casing (lead dioxide)
Negative electrode ----' (lead)
c,__ _____ Cell divider
280 Chapter 8 Chemistry of Some Corrosive Materials
SULFURIC ACID
@ UN
2795 , Sulfuric acid, (contains less than 51% acid)
DANGER Keep out _of reach of children. May be harmful if swallowed. Causes severe skin burns and d . F t I "f • h I eye amage. May be corrosive to metals. a a
1 ,n a ed. Harmful to aquatic life.
Do not breathe furn • . es, mist, vapors, or spray. Absorb spillage to
ire~en_t ;iaterial damage. Store in corrosion-resistant container or al n h~it a resistant inner liner. Wear protective gloves protective c ot mg eye t · '
. , pro ect,on, and face protection. Wear respiratory protection.
FIRST-AID INSTRUCTIONS:
IF IN EVES: Rinse cautiously with water for several minutes. Remove contac~ lenses, if present, and easy to do. Continue rinsing. Immediately call POISON CENTER or doctor.
IF SWALLOWED: Immediately call POISON CENTER or doctor.
IF ON SKIN: Remove immediately all contaminated clothing. Rinse skin with water.
Read Safety Data Sheet before use.
My Company My Street
My Town, My State 00000 Telephone (000) 000-0000
8.7-A PRODUCTION OF SULFURIC ACID Sulfuric acid is prepared at industrial plants by first burning sulfur to produce sulfur diox- ide, and then oxidizing the sulfur dioxide further in the presence of a catalyst to produce sulfur trioxide. This is the acidic anhydride of sulfuric acid. It reacts with water to form sulfuric acid.
However, sulfur trioxide does not unite with pure water readily. When sulfuric acid is manufactured industriaily, the sulfur trioxide is absorbed into a solution of sulfuric acid containing 97% sulfuric acid by mass instead of pure water. Sulfur trioxide readily dis- solves in this sulfuric acid solution. The final solution boils at 640°F (338°C) at 14.7 psia (!~1.3 kPa) and contains 98.3 % sulfuric acid by mass. In commerce, this solution is iden- tified as concentrated sulfuric acid. Emergency responders may encounter it in a variety of containers such as those illustrated in Figures 6.1 and 6.2. 8 ' 7 " 8
THE HAZARD ASSOCIATED WITH DILUTING Wbe SULFURIC ACID WITH WATER . . the en c?ncentrated sulfuric acid is diluted with water, considerable heat 1s re_leased to alw nvironment. Because this reaction is highly exothermic, extreme caution must illendes be exercised when diluting concentrated sulfuri~ aci~ ~ith water. The recom- suJf d Practice · l 1 h 'd · to water while stirrmg. When concentrated
Uric acid is d~sl to ds ~w yhpour t e act m .. localized boiling and violent spattering 1 ute m t e reverse manneL,
FIGURE 8 .4 This label affixed to nonbulk con- tainers of sulfuric acid complies with OSHA regu- lations published at 29 C.F.R . §1910 . 1200(f).
Chapter 8 Chemistry of Some Corrosive Materials 281
I
I I
I
Oleum
oleum (fuming sulfuric acid) Concentrated sulfuric acid containing additional dissolved sul- fur trioxide
occur that results in the production of a fume. When inhaled, the sulfuric acid fum pose the risk of inhalation toxicity. e can
8 . 7-C DEHYDRATING ACTION OF CONCENTRATED SULFURIC ACID Concentrated sulfuric acid possesses a capability for extracting water from certain Ill . als. In certain instances, it is even capable of extracting the elements of water. This tteri. ability is especially strong with organic compounds. Upon their contact, carbon is a;:er the only visibly remaining residue. It is for this reason that concentrated sulfuri
O ~n
completely destroys wood, textiles, and paper. This dehydrating phenomenon also~ acid when concentrated sulfuric acid burns body tissues. cc11rs
The ability of sulfuric acid to extract water is put to beneficial use during many ch ical manufacturing processes. The manufacture of the explosive nitroglycerin, for ex em. ple, uses sulfuric acid catalytically to extract the elements of water from glycerol:~ nitric acid (Section 15.6). n
8. 7-D OXIDIZING POTENTIAL OF CONCENTRATED SULFURIC ACID Hot, concentrated sulfuric acid reacts as a strong oxidizing agent. For example, copper, carbon, and lead are oxidized by hot, concentrated sulfuric acid as follows:
Cu (s) + 2H2S04( cone) CuS04(aq) + S02(g ) + 2H20(g) Copper Sulfuric acid Copper(II) sulfate Sul fur dioxide Water
C(s) + 2H2S04(conc) C02(g) + 2S02(g ) + 2H20(g ) Carbon Sulfuric acid Carbon dioxide Sul fur di oxide Water
Pb(s ) + 3H2S04( cone) Pb(HS04)2(s) + S02(g) + 2H20(g) Lead Sulfuric acid Lead(II) bisulfate Sulfu r dioxide Water
When the concentrated acid is at room temperature, however, it reacts so slowly with these elements that the oxidation is barely perceptible.
8.7-E ILL EFFECTS CAUSED BY INHALING THE VAPORS, MISTS, AND FUMES OF SULFURIC ACID
The repeated inhalation of sulfuric acid vapors, mists, and fumes by workers in occupa- tional settings has been linked with the onset of larynx, paranasal sinus, and lung cancer. These airborne forms of sulfuric acid are generated during the manufacture and use of sulfuric acid, especially the use of the acid for pickling. Given its potential to cause cancer, all work with sulfuric acid should be conducted only within a workplace that provides adequate ventilation.
8 .7-F WORKPLACE REGULATIONS INVOLVING SULFURIC ACID In the workplace, OSHA requires employees to limit employee exposure to a maximum sulfuric acid vapor concentration of 1 milligram/cubic meter, averaged over an 8-hour workday.
8 .7-G OLEUM (FUMING SULFURIC ACID) Sulfur trioxide dissolves in concentrated sulfuric acid, producing a thick, fuming yello~ liquid. When this liquid contains a higher proportion of sulfur trioxide than is fou nd 1.0
ordinary sulfuric acid, the resulting material is called oleum, or fuming sulfuric acid. T~s acid is available commercially with varying concentrations of sulfur triqxide up to 99,9 ~d Although oleum was formerly used in the petroleum refining industry, hydrofluoric ac~ (Section 8.11) now serves the same purpose. Today, oleum is used primarily within t e chemical industry.
282 Chapter 8 Chemistry of Some Corrosive Materials
TABLE 8.5 Shipping Descriptions of Sulfuric Acid
FORM OF SULFURIC ACID
Sulfuric acid (contains less than 51 % sulfuric acid)
Sulfuric acid (contains more than 51 % sulfuric acid)
SHIPPING DESCRIPTION•
UN2796, Sulfuric acid, 8, PG II
UN1830, Sulfuric acid, 8, PG II
sulfuric acid, spent UN1832, Sulfuric acid, spent, 8, PG 11 ----------+~__:_:__:_ ___ ......:..._ __ -::-::--:--- Su If uric aci d, fuming (contains less than 30% UN1831 , Sulfuric acid, fuming, 8, PG I
sulfur trioxide) ---------------1-------------:--:::-:-:--::-=--:- Sulfuric acid, fuming (contains 30% or more UN1831, Sulfuric acid, fuming, 8, (6.1), PG I sulfur trioxide) (Poison - Inhalation Hazard, Zone B) __________ L...:___:_:_ _________ ----:-
'W hen shippers know the actual concentration of sulfuric acid or sulfur tr ioxide in the acid that Is transported, DOT requires them to identify the concentration in lieu of a concentration range.
The chemical formula of oleum is often denoted as xH2SO 4 • yS 0 3, where x and Y are rhe number of moles of sulfuric acid and sulfur trioxide, respectively. For example, oleum that contains 1 mole of sulfur trioxide ( 80.1 g) for each mole of sulfuric acid (98.1 g) has the fo rmula H 2S2O7, because in this instance, x = y = 1. Oleum containing 65% sulfur trioxide by mass is expressed by the formula 4H2SO 4 • 9SO 3•
Because oleum contains dissolved sulfur trioxide, it has an elevated vapor pressure compared to the value for concentrated sulfuric acid (<0.001 mmHg) . The vapor pres- sure for oleum varies according to the concentration of dissolved sulfur trioxide but ranges from 342 mmHg to 433 mmHg at 68°F (20°C). This means that fuming sulfuric acid poses the risk of inhalation toxicity.
Like sulfuric acid, oleum is a corrosive material. It severely burns the skin, which generally heals to produce ugly scars. In addition, oleum spontaneously releases toxic sulfur trioxide vapor, which poses the potential risk of inhalation toxicity. Consequently, oleum should be stored and used only in a well-ventilated location.
8.7-H TRANSPORTING SULFURIC ACID DOT regulates the transportation of four forms of sulfuric acid: a liquid having 51 % or more acid; a liquid with less than 51 % acid; a spent sulfuric acid solution; and fuming sulfuric acid. When these acids are offered for transportation, DOT requires their ship- pers to provide the relevant shipping description shown Table 8.5 on the accompanying shipping paper. The Hazardous Materials Table at 49 C.F.R. § 172.101 lists several con- centrations of sulfuric acid . DOT requires shippers to parenthetically include an appro- priate modifier like "contains" or "containing" between the shipping name and the hazard class or following the shipping description. All other labeling, marking, and plac- arding requirements apply.
S.8 NITRIC ACID Nitric acid is second among the acids most commonly used throughout the United
~.1Y Slates. It is the raw material used for the manufacture of ammonium nitrate fertilizers , oQ ~ explosives, dyes perfumes drugs and nitrated organic compounds . Its use is also
17, 1J req · ' ' '
.il l' uired for the production of pat ent leather and related fabrics. The chemical for- ~~1 ¥ lllula of nitric acid is HN0 3 . Some of its important physical properties are provided ,,II" in 1'able 8.6 .
Nitric acid
Chapter 8 Chemistry of Some Corrosive Materials 28;
TABLE 8.6 Physical Properties of Concentrated Nitric Acid
Melting point -44°F (-42°C)
Boiling point 187°F (86°C)
Specific gravity at 68°F c20°c) 1.50
Vapor density (air= 1) 3.2
Vapor pressure at 68°F (20°C) 47.9 mmHg
Solubility in water Infinitely soluble
Pure nitric acid is a colorless liquid. It is encountered commercially in concentrat d and diluted forms. Concentrated nitric acid is an aqueous solution consisting of 68.2~ nitric acid by mass. All concentrations containing less than 68.2 % acid are forms 0; diluted nitric acid.
When encountered, nitric acid is often yellow to red-brown in color, which indicates that nitrogen dioxide is present. Nitrogen dioxide is a red-brown gas produced by the slow decomposition of nitric acid, a reaction catalyzed by sunlight.
4HN03(l) 4N02(g) + 2H20(l) + Oz(g) Oxygen Nitric acid Nitrogen dioxide
Water
8.8-A PRODUCTION OF NITRIC ACID Almost all nitric acid is industrially manufactured from ammonia by means of a series of reactions. Gaseous ammonia is first mixed with about 10 times its volume of air, and then exposed to platinum gauze. The platinum increases the rate of the reaction that converts ammonia into nitric monoxide (NO ). Then, additional air is permitted to enter the reac- tion system so the nitrogen monoxide can be further oxidized to nitrogen dioxide.
4NH3(g) + 50z(g) 4NO(g) + 6H20(g) Water
Ammonia Oxygen Nitrogen mo nox ide
2NO(g) + Oz(g) 2N02(g) Nitrogen monoxide Oxygen Nitrogen dioxide
The nitrogen dioxide is then reacted with water to produce nitric acid.
3N02(g) + H20(l) 2HN03(l) + NO(g) Nitrogen dioxide Water
Nitric acid Nitroge n monoxide
The excess nitrogen monoxide produced in this reaction is recycled through the system,
/
8.8-B OXIDATION OF METALS BY NITRIC ACID Like hot, concentrated sulfuric acid, nitric acid is an oxidizing acid, even when it is diluted 1 with water at room temperature. When metals are chemically attacked by nitric acid, theY are oxidized to their corresponding positive ions and the nitric acid is reduced to one or more of the following: nitrogen, nitrogen monoxide, nitrogen dioxide, dinitrogen mono"· ide, or the ammonium ion. Nitric acid reacts with some metals to form each of these products under specific conditions. For example, it reacts with zinc to form nitrogen, nitrogen ~onoxide, nitrogen dioxide, dinitrogen monoxide, or ammonium nitrate in sW arate reactions.
284 Chapter 8 Chemistry of Some Corrosive Materials
5Z n(s) + 12HNO 3(aq) ----,. 5Zn(N O 3)z(aq ) + 6 H 2O (/) + Nz(g) Zinc N itric acid Zinc ni trate Wate r N itrogen
3Zn(s) + 8HNO3(aq) ----,. 3Zn(N O 3)z(aq) + 4HzO([) + 2NO(g) Zinc Nitric ac id Zinc nilrate Wate r N itroge n monoxide
Z n(s) + 4H NO3(co11 c) ----,. Zn(NO3)z(aq) + 2H2O(/) + 2NOz(g) Zinc N itri c acid Zinc nitrate Water N itroge n d iox ide
4Zn(s) + I 0HNO3(aq) - 4 Z n(NO3)z(aq) + 5H2O (/) + N2O(g) Zinc Ni tric ac id Z i nc nitrate Wate r Dini trogen m o nox ide
4zn(s) + I 0HNO3(aq) - 4Zn(NO3)z(a q) + 3H2O(/) + NH4N O 3(aq) Zinc N itric ac id Z inc nitra te Wate r Ammonium nitrate
• rhe combination of these reactions that defines the corrosivity of nitric acid. It is When nitric acid oxidizes a metal, the most common products formed are nitro- en monoxide and nitrogen dioxide. In general, diluted nitric acid oxidizes metals to
g roduce nitrogen monoxide, and concentrated nitric acid oxidizes metals to produce P d. .d ·rrogen wx1 e. ni On occasion, chemists use a nitrating solution to oxidize metals that are ordinar- ily considered unreactive . . T?e most common solution used for this purpose is a 1 :3 mixture of concentrated mtnc and hydrochloric acids called aqua regia. It is one of a limited number of mixtures known to react with metallic gold. The nitric acid oxi- dizes the hydrochloric acid, as follows:
HN03(aq) + 3HCl(aq) - NOCl(g) + C l2(g) + 2H20(/) Nitric acid Hydrochloric acid Nitrosyl chloride Chlorine Water
Nitrosyl chloride has a reddish-yellow color; hence, aqua regia is also reddish-yellow.
8.8-C OXIDATION OF NONMETALS BY NITRIC ACID Hot nitric acid corrodes nonmetals. For example, carbon and sulfur are oxidized by hot, concentrated nitric acid as depicted by the following equations:
C(s) + 4HN03(conc) --+ C02(g) + 4N02(g) + 2H20([) Carbon Nitric acid Carbon dioxide Nitrogen di oxide Water
Ss(s) + 48HN03(conc) ._ 8H2S04(l) + 48NOz(g) + 16H20([) Sulfur Nitric acid Sulfuric acid Nitrogen diox ide Water
8.8-D OXIDATION OF ORGANIC COMPOUNDS BY NITRIC ACID Nitric acid oxidizes many flammable organic compounds, sometimes at explosive rates. This results in their subsequent ignition. For example, the organic compounds turpentine, a~etic acid, acetone, ethanol, nitrobenzene, and aniline react so vigorously when mixed With hot, concentra ted nitric acid that they burst into flame.
8 · 8 ·E REACTIONS OF NITRIC ACID WITH CELLULOSIC MATERIALS
Nitric ac·d · bl · · · f d l · d h c II . 1 ts capa e of initiating the spontaneous 1grut1on o woo , exce s10r, an ot er r: ulosic materials, especia11y when these materials have been finely divided. It is for this ar:son that bottles of nitric acid are not cushioned with a cellulosic materia l when they
transported.
8,8.F ILL t-r . EFFECTS CAUSED BY EXPOSURE TO NITRIC ACID
Itr1c acid . . . h their corrodes body tissues by reacting with the complex protems t at make up st
ructures. The exposure of n itr ic acid to the skin results in ugly, yellow burns that
aqua regia A 1 :3 mix- ture of concentrated nitric acid and hydro- chloric acid
Chapter 8 Chemistry of Some Corrosive Materials 285
heal very slowly. The chemistry associated with this phenomenon involves the of a yellow-brown substance called xanthoproteic acid. The discoloration of thpri~Uction cally wears away in two to three weeks. es lil typi.
7
SOLVED EXERCISE 8.2
Fuming nitric acid
Metallic copper does not replace the hydrogen in nitric acid, but metallic copper does react with nit • . these reactions_ the nitric acid reacts as ~n _oxidizing agent. What are the products of the reactions in w~:~tid . 1n lie copper 1s ox1d1zed by concentrated nitric acid and diluted nitric acid? rnetal.
S~lution: Concentrated ~itric acid oxidizes metals to produce nitrogen dioxide, ":'hereas diluted nitric acid . d1zes metals to produce nitrogen monoxide. The metal is oxidized to the copper(II) ,on. oxi.
Cu (s) + 4H NO3(conc) - Cu(N O3)2(aq) + 2NOz(g) + 2H2O(/) Copper Nitric acid Copper(/1) ni tra te Nitrogen dioxide Water 3Cu(s) + 8HN03(dil) - 3C u(NO3)2(aq) + 2NO(g) + 4H2O(/) Copper Nitric acid Copper(/1) nitrate Nitrogen monoxide Water
8.8-G FUMING NITRIC ACID The oxides of nitrogen are readily soluble in concentrated nitric acid. When the acid contains a higher proportion of nitrogen oxides than is contained in ordinary nitric acid, the resulting material is called fuming nitric acid, of which there are two varieties:
Red fuming nitric acid contains more than 85% nitric acid, less than 5% water, and from 6% to 15% nitrogen oxides. Red fuming nitric acid containing 70% acid and 6% to 15% nitrogen oxides has a vapor pressure of 49 mmHg at 68°F (20°C}. White fuming nitric acid contains more than 97.5% nitric acid, less than 2% water, and less than 0.5% nitrogen oxides. It has a vapor pressure of 57 mmHg at 77°F (25°C). This second form is not widely encountered because it slowly reverts to the red form. Contact of the skin with fuming nitric acid is highly irritating. In addition, the red
form spontaneously releases toxic nitrogen oxide vapor, which poses the risk of inhalation toxicity. For this reason, fuming nitric acid should always be segregated from other chem· ical substances and stored and used in weII-ventilated locations.
8.8-H WORKPLACE REGULATIONS INVOLVING NITRIC ACID In the workplace, OSHA requires employers to limit employee exposure to a maximum nitric acid vapor concentration of 2 ppm, averaged over an 8-hour workday, and 4 ppm for a short-term exposure.
8.8-1 TRANSPORTING NITRIC ACID When shippers offer nitric acid or fuming nitric acid for transportation, DO_r requires them to identify the appropriate substance with the relevant entry shown ~n Table 8. 7 on the accompanying shipping paper. When carriers transport nitric acid by highway or rail, DOT requires them to display the name NITRIC A CID on tW
0
opposing sides of the transport vehicle. All other labeling, marking, and placarding requirements apply.
286 Chapter 8 Chemistry of Some Corrosive Materials
Representative Shipping Descriptions of Nitric Acid CID Of NITRIC A SHIPPING DESCRIPTION
f0~NI 'd other t han red fuming , w ith not UN2031, Nitric acid, 8, PG I Nitric aci ' ]O'/o nitric acid
ore than 111 'd other than red fum ing, with more
UN2031, Nitric acid, 8, (5 .1), PG II •c ac1 , 'd Nitrl % nitric acI an 70
th .d mixtures, spent, with more than UN1796, Nitrating acid mixtures, spent, 8, ·tric ac1 'd NI •tric acI (5.1), PG I o¾ n1
S .d mixtures, spent, with not more than UN1826, Nitrating acid mixtures, spent, 8, PG 11 ·tric ac1 'd N1 ·tric acI o¾ n1
S 'd mixtures w ith more than UN1796, Nitric acid mixtures, 8, (5 .1), PG I itric ac1 . N ¾ nitric acid
so 'd mixtures with not more than UN1796, Nitric acid mixtures, 8, PG II Nitric ac1 _ . ¾ nitric acid
so df . ' h . . cid, other th~n r~ urning, wit not UN2031, Nitric acid, 8, PG II N1tr1C ah 2oo/o nitri c acid moret an . .
•ng nitric acid with not more than UN2032, Nitric acid, red fuming, 8, (5. 1, 6.1 ), Red fum1 . o¾ nitric acid PG I (Po ison - Inhalation Hazard, Zone B) 7
d f . · . "d other than re urning, with more UN2031, Nitric acid, 8, (5.1 ), PG I Nitric ac1 ' . JOo/o nitric acid than
. 'd other than red fuming, with not UN2031, Nitric acid, 8, PG 11 N'tnc ac1 , . . 1 Oo/o nitric acid n,orethan 2
8,9 HYDROCHLORIC ACID H drochloric acid is ~nother comm_ercially important acid. It is most familiar to the gen- er~l public as a const1~ue~t of certam ~ous~hold cleaning products like Lysol Toilet Bowl Cleaner. It also is the ltqmd used to mamtam the proper acidity of the water in residential
d public swimming pools. an Outside the home, hydrochloric acid has many other uses. As a component of pickle liquor, it is used for galvanizing, tinning, and enameling. In the food industry, hydrochloric acid is used as a processing agent during the production of certain food products such as corn syrup. It is used in the petroleum industry to activate petroleum wells, and it is used in the chemical industry to manufacture and produce dozens of important compounds. Hydrochloric acid is frequently encountered in educational and research facilities, where it usually stored in nonbulk plastic containers like those shown in Figure 6.1.
Pure hydrochloric acid is a colorless, fuming, and pungent-smelling liquid composed 1 of hydrogen chloride dissolved in water. The chemical formulas of hydrochloric acid and
hydrogen chloride are HCl(aq ) and HCl(g), respectively. Some physical properties of the concentrated acid and its vapor are noted in Table 8.8.
' a,g,A PRODUCTION OF HYDROCHLORIC ACID Hydrochloric acid is prepared by dissolving anhydrous hydrogen chloride in water. The ~~:ntra~ed ~cid contains from 36% to 38% hydrogen chlori~e by_ mass and is ~ol?rles~.
r. _Purity is not a factor the industrial grade of hydrochloric acid called muriatic acid 01 [en is d · ' · th · 1· htl 11 d tothe use · It 1s a dilute solution of undefined concentration at 1s s 1g Y ye ow ue
Presence of metal impurities like iron salts.
Hydrochloric acid
} \,1\
Chapter 8 Chemistry of Some Corrosive Materials 28~
TABLE 8.8 Physical Properties of Hydrochloric Acid and Its Vapor
HCI (cone) HCI (g)
Melting point - 101 °F (-74°C) -174•F (114'C)
Boiling point 127°F (53°C) -121'F (-8S'C)
Specific gravity at 68°F (20°C) 1.18 1.27
Vapor density (air = 1) 1.3 1.3
Vapor pressure at 68°F (20°() 150 mmHg 30,780 mmHg
Solubilit in water y 85 /100 g g of H O at 68°F (20°C) 67% at 68' 0 F (20 q
8 .9-B ILL EFFECTS CAUSED BY INHALING HYDROGEN CHLORIDE The principal hazardous feature of hydrochloric acid is associated with inhaling th hydrogen chloride vapor released spontaneously from the ~onc~ntra_ted acid. Hydroge~ chloride is a poisonous gas. When concentrated hydrochlonc acid spills or leaks from its container, the pungent odor of its toxic vapor is immediately detectable. Because the vapor is approximately one-fifth heavier than air, it lingers in low areas, where it can pose a risk to health and safety.
When hydrogen chloride vapor is encountered, individuals experience the symptoms noted in Table 8.9. In the worst situations, prolonged exposure to massive amounts of hydrogen chloride causes pulmonary edema (Section 7.3-B), which can completely dete- riorate the tissue cells within the respiratory tract and destroy its lining.
TABLE 8.9 Ill Effects Caused by Inhaling Hydrogen Chloride
HYDROGEN CHLORIDE (ppm) SYMPTOMS
1-5 Threshold limit for detection of smell
5-10 Mild irritation of mucous membranes, eyes, nose, and throat
35 Distinct irritation of mucous membranes, eyes, nose, and throat
5-100 Barely tolerable effects including severe coughing and panic; possible injury to the bronchial region
1000 Danger of pulmonary edema after 24-hr exposure; potentially fatal
SOLVED EXERCISE 8.3 Use the data in Tables 8.4 an d 8.8 to determine whether each of the following aci ds poses the greater haza rd by inhalation toxicity at 68°F (20°C) when all other factors are considered equally: (a) concentrated sulfuric acid or concentrated hydroch loric acid; (b) oleum or concentrated hydrochloric acid.
Solution: (a) To pose an inhalation toxicity hazard, the liq uid aci d must produce sufficient vapor at 68°F (20' Cl to
cause illness or death when inhaled . In Table 8.4, the vapor pressure of concentrated sulfuric acid 15
listed as < 0.001 mmHg . This low val ue si gn ifies that vi rtually no vapor is produced at this temperature. Accordingly, exposure to concentrated sulfuric aci d poses a very low risk of inhalation toxicity. However, the vapor pressure of hydrochloric aci d is listed in Table 8.8 as 150 mm Hg . This elevated value indicates that when in haled, hydrochlori c aci d produces suffi ci ent vapor at 68•F (2o•c) to cause the ill effects noted in Table 8.9.
288 Chapter 8 Chemistry of Some Corrosive Materials
I
oieurn, or f~rning s~lfuric acid, has _ a ~aper pressure ranging from 342 mm Hg to 433 mm Hg at 68°F (b) (Z0°C) since it contains f~ee s_ulfur trioxide. Hence, it poses a greater risk of inhalation toxicity than does
concentrated hydroch~oric acid . Non~:heless, _some caution must be exercised with the use of the phrase "all other factors considered equally. _ In particular, sulfur trioxide is a cancer-causing substance whereas hydrogen chlorid e is not. On ~his basis alone, health officials are likely to cons ider that oleum poses a greater risk of inhalation tox1c1ty than does concentrated hydrochloric acid .
C REACTIONS OF HYDROCHLORIC ACID WITH s.9· OXIDIZING AGENTS
d ochloric acid is chemically incompatible with oxidizing agents such as metallic chlo- rlY r metallic dichromates, and metallic permanganates. These reactions result in the races, . hl .
d Ction of toxic c orme. pro u KC103(s) + 6HCl(conc) K Cl(aq) + 3H20(l) + 3Clz(g)
Poiassi urn chl orate Hydrochloric acid Potassium chloride Water Chlorine
K2Cr20 7(s) + l4HCl (conc) 2KCl(aq) + 2CrCI 3(aq) + 7H20 (/) + 3Clz(g) Potassium dichromate Hydroc hloric acid Potassium chloride Chromium(HI) chlo ride Water Chl orine
2KMn04Cs) + 16HCl(conc) 2MnCI2(aq) + 2KCl(aq) + 8H20 (l) + 5C lz(g) Poiassiurn permanganate Hydroc hl oric ac id Manganese(Il) chloride Potassiu m chlori de Water Chlorine
To reduce or eliminate the likelihood of an unwanted reaction between hydrochloric acid and chlorine-producing pool chemicals, acid manufacturers often label their contain- ers with a message like the following:
DO NOT STORE NEAR CHLORINE-PRODUCING
POOL CHEMICALS
8.9-D ANHYDROUS HYDROGEN CHLORIDE Anhydrous hydrogen chloride itself is a commercial chemical product that is prepared by the direct combination of elemental hydrogen and chlorine.
H2(g) + Clz(g) 2HC l(g) Hydrogen Chlorine Hydrogen chlolide
Hydrogen chloride is also produced as a by-product during the chlorination of organic compounds.
8·9·E WORKPLACE REGULATIONS INVOLVING HYDROGEN CHLORIDE t the Workplace OSHA requires employers to limit employee exposure to a maximum
Ydrogen chlorid~ vapor concentration of 5 ppm, which should not be exceeded during any Pan f h 0 t e working exposure.
S,g.F TRANSPORTING HYDROCHLORIC ACID AND ANHYDROUS HYDROGEN CHLORIDE
Do~ shippers offer hydrochloric acid or anhydrous hyd~o~en chlorid~ for transportation, aeco reqwres them to provide the relevant shipping description show~ m Table 8._10 on the rail tnpanying ship · Wh hydrogen chloride is transported m bulk by highway or 'Iv 'bo1 also re ~mg pap~r. en k the bulk packaging on two opposing sides with the
ords INZJ quires earners to mar d 1 din • 1 o.ALATION HAZARD. All labeling, marking, an p acar g reqwrements app y.
Anhydrous hydrogen chloride
Chapter 8 Chemistry of Some Corrosive Materials 289
I I I
Perchloric acid
TABLE 8.10 Shipping Descriptions of Hydrochloric Acid and Hydrogen Chloride
HYDOCHLORIC ACID/HYDROGEN CHLORIDE SHIPPING DESCRIPTION
Hydrochloric acid
Hydrogen chloride, anhydrous
Hydrogen chloride, cryogenic liquid
8.10 PERCHLORIC ACID
UN1789, Hydrochloric acid, 8, PG 11
or UN 1789, Hydrochloric acid, 8, PG 111
UN1050, Hydrogen chloride, anhydrous 23 (Poison - Inhalation Hazard, Zone C} ' · '(B),
UN2186, Hydrogen chloride, refrigerated I' . 2.3, (8), (Poison - Inhalation Hazard, Zone tjUid,
Perchloric acid is an acid used primarily by the chemical, electroplating, and incendiary (fireworks) industries. Its chemical formula is HCl04 .
8 .10-A PRODUCTION OF PERCHLORIC ACID Concentrated perchloric acid is prepared by distilling a mixture of potassium perchlorate 1 and sulfuric acid at reduced pressure (i.e., lower than atmospheric pressure). The chemical reaction associated with its production follows:
Potassi um perchlorate Sulfuri c acid Perchloric ac id Potassium sulfate
The acid is a colorless, aqueous liquid having an approximate composition of 72% by mass. This is the composition of the concentrated perchloric acid available commercially. Although solutions of perchloric acid having an acid concentration greater than 72% are known, they are not routinely encountered, because they are explosively unstable. Some physical properties of concentrated perchloric acid are noted in Table 8.11.
8 .10-B THERMAL DECOMPOSITION OF PERCHLORIC ACID Concentrated perchloric acid may be safely heated to 194°F (90°C), but above this tern· perature, it is likely to explosively decompose as follows:
Perchloric acid Chlorine Oxygen Water
TABLE 8.11 Physical Properties of Concentrated Perchloric Acid
Melting point 0°F (-18°C)
Boiling point 397°F (203°C)
Specific gravity at 68°F (20°C) 1.70
Vapor density (air= 1) 3.5
Vapor pressure at 68°F (20°C) 6.75 mmHg
Solubility in water Very soluble
290 Chapter 8 Chemistry of Some Corrosive Materials
