Acids, Bases and Neutralization Reactions ACIDS Many Acids and Bases Are Industrial and Household Substances and Some Are Important Components of Biological ﬂuids

Reactions in aqueous solutions Acids, Bases and Neutralization reactions ACIDS Many acids and bases are industrial and household substances and some are important components of biological ﬂuids. Hydrochloric

acid (HCl), for example, is an important industrial chemical124 CHAPTER 4andReactions the in Aqueous Solution main constituent of gastric juice in your stomach. equations for precipitation reactions, the anions and cations appear to exchange partners. Thus, 2+ 2- + - we put Ca and CO3 together to give CaCO3 and Na and Cl together to give NaCl. Accord- ing to the solubility guidelines in Table 4.1, CaCO3 is insoluble and NaCl is soluble. The balanced molecular equation is

CaCl2 aq + Na2CO3 aq ¡ CaCO3 s + 2 NaCl aq . In a complete ionic equation,1 2 only dissolved1 2 strong electrolytes1 2 (such as1 soluble2 ionic com- Acids and bases are also common electrolytes pounds) are written as separate ions. As the (aq) designations remind us, CaCl2,Na2CO3,and NaCl are all dissolved in the solution. Furthermore, they are all strong electrolytes. CaCO3 is an ionic compound, but it is not soluble. We do not write the formula of any insoluble compound as its component ions. Thus, the complete ionic equation is į FIGURE 4.5 Vinegar and lemon juice 2+ - + 2- are common household acids. Ammonia Ca aq + 2 Cl aq + 2 Na aq + CO3 aq ¡ and baking soda (sodium bicarbonate) + - CaCO3 s + 2 Na aq + 2 Cl aq are common household bases. 1 2 1 2 1 2 1 2 - + Acids are substances that ionize in aqueous solutions to Cl and Na are spectator ions. Canceling them gives the following1 2 net ionic1 equation:2 1 2 Ca2+ aq CO 2- aq CaCO s + + 3 ¡ 3 form hydrogen ions H (aq). As a hydrogen atom consists of a Check We can check our result1 by2 confirming1 that2 both the elements1 2 and the electric charge are balanced. Each side has one Ca, one C, and three O, and the net charge on each side equals 0. + Comment If none of the ions in an ionic equation is removed from solution or changed in proton and an electron, H is simply a proton. some way, all ions are spectator ions and a reaction does not occur. Thus, acids are also called proton donors. PRACTICE EXERCISE Write the net ionic equation for the precipitation reaction that occurs when aqueous solutions of silver nitrate and potassium phosphate are mixed.

+ 3- Answer: 3 Ag aq + PO4 aq ¡ Ag3PO4 s 1 2 1 2 1 2 4.3 ACIDS, BASES, AND NEUTRALIZATION | REACTIONS Many acids and bases are industrial and household substances (ǡ FIGURE 4.5), and some are important components of biological fluids. Hydrochloric acid, for example, is an important industrial chemical and the main constituent of gastric juice in your stomach. Acids and bases are also common electrolytes. Hydrochloric acid, HCl Acids As noted in Section 2.8, acids are substances that ionize in aqueous solution to form hydrogen ions H+ aq . Because a hydrogen atom consists of a proton and an electron, H+ H is simply a proton. Thus, acids are often called proton donors. Molecular models of three common acids are1 shown2 in ǡ FIGURE 4.6. Protons in aqueous solution are solvated by water molecules, just as other cations Cl are [Figure 4.3(a)]. In writing chemical equations involving protons in water, therefore, we write H+ aq . N Molecules of different acids ionize to form different numbers ofH+ ions. Both HCl Nitric acid, HNO 1 2 + 3 and HNO3 are monoprotic acids, yielding one H per molecule of acid. Sulfuric acid, + O H2SO4,is a diprotic acid, one that yields two H per molecule of acid. The ionization of H2SO4 and other diprotic acids occurs in two steps: + - C H2SO4 aq ¡ H aq + HSO4 aq [4.9] - + 2- HSO4 1 aq2 ∆ H 1 aq2 + SO4 1aq2 [4.10] Although H2SO4 is a strong1 electrolyte,2 1 only2 the first ionization1 2 (Equation 4.9) is complete. Thus, aqueous solutions of sulfuric acid contain a mixture ofH+ aq , - 2- HSO4 aq , and SO4 aq . Acetic acid, CH3COOH 1 2 The molecule CH3COOH (acetic acid) that we have mentioned frequently is the primary1 component2 in vinegar.1 2 Acetic acid has four hydrogens, as Figure 4.6 shows, but į FIGURE 4.6 Molecular models of three common acids. only one of them, the H in the COOH group, is ionized in water. The three other hydrogens are bound to carbon and do not break their C ¬ H bonds in water. 124 CHAPTER 4 Reactions in Aqueous Solution

equations for precipitation reactions, the anions and cations appear to exchange partners. Thus, 2+ 2- + - we put Ca and CO3 together to give CaCO3 and Na and Cl together to give NaCl. Accord- 124 CHAPTER 4 Reactions in Aqueous Solution ing to the solubility guidelines in Table 4.1, CaCO3 is insoluble and NaCl is soluble. The balanced molecular equation is

CaCl2 aq + Na2CO3 aq ¡ CaCO3 s + 2 NaCl aq equations for precipitation reactions, the anions and cations appear to exchange partners. Thus, 2+ 2- In a complete ionic+ equation,- only dissolved strong electrolytes (such as soluble ionic com- we put Ca and CO3 together to give CaCO3 and Na and1 Cl2 together 1to give2 NaCl. Accord-1 2 1 2 pounds) are written as separate ions. As the (aq) designations remind us, CaCl2,Na2CO3,and ing to the solubility guidelines in Table 4.1, CaCO3 is insoluble and NaCl is soluble. The balanced NaCl are all dissolved in the solution. Furthermore, they are all strong electrolytes. CaCO3 is an molecular equation is ionic compound, but it is not soluble. We do not write the formula of any insoluble compound as its component ions. Thus, the complete ionic equation is į FIGURE 4.5 Vinegar andCaCl lemon2 aq juice+ Na2CO3 aq ¡ CaCO3 s + 2 NaCl aq 2+ - + 2- are commonIn ahousehold complete acids. ionic Ammoniaequation, only dissolvedCa aq strong+ 2 Cl electrolytesaq + 2 Na (suchaq as+ COsoluble3 aq ionic¡ com- and baking soda (sodium bicarbonate)1 2 1 2 1 2 1 2 + - pounds) are written as separate ions. As the (aq) designations remind us, CaCl ,Na COCaCO,and3 s + 2 Na aq + 2 Cl aq are common household bases. 1 2 1 2 1 2 2 1 2 3 NaCl are all dissolved in the solution. Furthermore,- + they are all strong electrolytes. CaCO is an Cl and Na are spectator ions. Canceling them gives the3 following1 2 net ionic1 equation:2 1 2 ionic compound, but it is not soluble. We do not write the formula of any insoluble compound 2+ 2- as its component ions. Thus, the complete ionic equation is Ca aq + CO3 aq ¡ CaCO3 s į FIGURE 4.5 Vinegar and lemon juice Check We can check our result by confirming that both the elements and the electric charge Ca2+ aq 2 Cl- aq 2 Na+ aq CO 2- aq 1 2 1 2 1 2 are common household acids. Ammonia + + are+ balanced.3 Each side¡ has one Ca, one C, and three O, and the net charge on each side equals 0. and baking soda (sodium bicarbonate) + - CaCO3 s + 2 Na aq + 2 Cl aq are common household bases. 1 2 1 2 1 2Comment 1If none2 of the ions in an ionic equation is removed from solution or changed in - + Cl and Na are spectator ions. Cancelingsome way, them all givesions arethe spectator following1 2 ions net and ionic a 1reaction equation:2 does not1 occur.2 2+ 2- Ca aq PRACTICE+ CO3 aq EXERCISE¡ CaCO3 s Write the net ionic equation for the precipitation reaction that occurs when aqueous solutions Check We can check our result1 by2 confirming1 that2 both the elements1 2 and the electric charge are balanced. Each side has one Ca, oneof silverC, and nitrate three andO, andpotassium the net phosphate charge on are each mixed. side equals 0. + 3- ACIDS Comment If none of the ions in anAnswer: ionic equation3 Ag aq is removed+ PO4 fromaq ¡ solutionAg3PO or4 changeds in some way, all ions are spectator ions and a reaction 1does2 not occur.1 2 1 2 PRACTICE EXERCISE Protons in aqueous solution are solvated byWrite water the net ionic molecules. equation for the4.3 precipitation InACIDS, writing reaction BASES, that occurs when AND aqueous NEUTRALIZATION solutions chemical equations involving protons in water,of silver nitratetherefore, and potassium wephosphate write |areREACTIONS mixed. H+ (aq). + 3- Answer: 3 Ag aq + PO4 aq Many¡ acidsAg3PO and4 s bases are industrial and household substances (ǡ FIGURE 4.5), and some are important components of biological fluids. Hydrochloric acid, for example, is 1 2 1 2an important + industrial1 2 chemical and the main constituent of gastric juice in your Molecules of different acids ionize to form different numbersstomach. of AcidsH and ions. bases are also common electrolytes. 4.3 ACIDS, BASES,+ AND NEUTRALIZATION Both HCl and HNO3 are monoprotic Hydrochloricacids, |yielding acid, HCl one HAcids per molecule REACTIONS As noted in Section 2.8, acids are substances that ionize in aqueous solution to form hy- of acid. + + Many acids and bases are industrialdrogen and ions household H aq . Because substances a hydrogen (ǡ FIGURE atom consists 4.5), andof a proton and an electron, H H is simply a proton. Thus, acids are often called proton donors. Molecular models of three some are important components of biological fluids.1 2 Hydrochloric acid, for example, is an important industrial chemicalcommon and the acids main are shown constituent in ǡ FIGURE of gastric 4.6 . juice in your stomach. Acids and bases are also commonProtons electrolytes. in aqueous solution are solvated by water molecules, just as other cations Cl are [Figure 4.3(a)]. In writing chemical equations involving protons in water, therefore, Hydrochloric acid, HCl Acids we write H+ aq . HCl HNO3 N Molecules of different acids ionize to form different numbers ofH+ ions. Both HCl NitricAs noted acid, inHNO Section 2.8, acids are substances1 that2 ionize in aqueous solution to +form hy- 3 and HNO3 are monoprotic acids, yielding one H per molecule of acid. Sulfuric acid, + + + drogen ions H aq . BecauseO a hydrogenH2SO4,is atom a diprotic consistsacid, of one a thatproton yields and two an H electron, per moleculeH of acid. The ionization of H is simply a proton. Thus, acids areH often2SO4 andcalled other proton diprotic donors acids. Molecular occurs in two models steps: of three 1 2 + Sulfuric acid, H2SO4, is a diprotic acid, it yieldscommon acidstwo are shownH perin ǡ FIGURE molecule 4.6. of + - C H2SO4 aq ¡ H aq + HSO4 aq [4.9] Protons in aqueous solution are solvated by water molecules, just as other cations - + 2- acid. The ionization of H2SO4 and otherCl diproticare [Figure 4.3(a)]. acids In writing occurs chemical in equations two involvingsteps:HSO4 1protons aq2 ∆ in water,H 1 aq2 therefore,+ SO4 1aq2 [4.10] + we write H aq . Although H2SO4 is a strong1 electrolyte,2 1 only2 the first ionization1 2 (Equation 4.9) is N + Molecules of different- acids ionizecomplete. to form Thus, different aqueous numbers solutions of ofH sulfuric+ ions. Both acid HCl contain a mixture ofH+ aq , 1) H2SO4 (aq) ⟶ H (aq) + HSO4 (aq) - 2- Nitric acid, HNO3 and HNO are1 2monoprotic acids,HSO yielding4 aq one, and H SO+ per4 moleculeaq . of acid. Sulfuric acid, Acetic acid, CH33COOH 1 2 The molecule+ CH3COOH (acetic acid) that we have mentioned frequently is the O H2SO4,is a diprotic acid, one that yields two H per molecule of acid. The ionization of primary1 component2 in vinegar.1 2 Acetic acid has four hydrogens, as Figure 4.6 shows, but - į FIGURE+ H2SO 4.64 andMolecular other modelsdiprotic2- of acids occurs in two steps: three common acids. only one of them, the H in the COOH group, is ionized in water. The three other hydro- 2) HSO4 (aq) ⟶ H (aq) + SO4 (aq) + - C H2SO4 aqgens¡ are boundH aq to carbon+ HSO and4 doaq not break their C ¬[4.9]H bonds in water. - + 2- HSO4 1 aq2 ∆ H 1 aq2 + SO4 1aq2 [4.10] Although H2SO4 is a strong1 electrolyte,2 1 only2 the first ionization1 2 (Equation 4.9) is complete. Thus, aqueous solutions of sulfuric acid contain a mixture ofH+ aq , - 2- HSO4 aq , and SO4 aq . Acetic acid, CH3COOH 1 2 The molecule CH3COOH (acetic acid) that we have mentioned frequently is the primary1 component2 in vinegar.1 2 Acetic acid has four hydrogens, as Figure 4.6 shows, but į FIGURE 4.6 Molecular models of three common acids. only one of them, the H in the COOH group, is ionized in water. The three other hydrogens are bound to carbon and do not break their C ¬ H bonds in water. 124 CHAPTER 4 Reactions in Aqueous Solution

equations for precipitation reactions, the anions and cations appear to exchange partners. Thus, 2+ 2- + - we put Ca and CO3 together to give CaCO3 and Na and Cl together to give NaCl. Accord- ing to the solubility guidelines in Table 4.1, CaCO3 is insoluble and NaCl is soluble. The balanced molecular equation is

CaCl2 aq + Na2CO3 aq ¡ CaCO3 s + 2 NaCl aq In a complete ionic equation,1 2 only dissolved1 2 strong electrolytes1 2 (such as1 soluble2 ionic compounds) are written as separate ions. As the (aq) designations remind us, CaCl2,Na2CO3,and NaCl are all dissolved in the solution. Furthermore, they are all strong electrolytes. CaCO3 is an ionic compound, but it is not soluble. We do not write the formula of any insoluble compound as its component ions. Thus, the complete ionic equation is į FIGURE 4.5 Vinegar and lemon juice 2+ - + 2- are common household acids. Ammonia Ca aq + 2 Cl aq + 2 Na aq + CO3 aq ¡ and baking soda (sodium bicarbonate) + - CaCO3 s + 2 Na aq + 2 Cl aq are common household bases. 1 2 1 2 1 2 1 2 - + Cl and Na are spectator ions. Canceling them gives the following1 2 net ionic1 equation:2 1 2 2+ 2- Ca aq + CO3 aq ¡ CaCO3 s Check We can check our result1 by2 confirming1 that2 both the elements1 2 and the electric charge are balanced. Each side has one Ca, one C, and three O, and the net charge on each side equals 0. Comment If none of the ions in an ionic equation is removed from solution or changed in some way, all ions are spectator ions and a reaction does not occur.

PRACTICE EXERCISE Write the net ionic equation for the precipitation reaction that occurs when aqueous solutions of silver nitrate and potassium phosphate are mixed.

+ 3- Answer: 3 Ag aq + PO4 aq ¡ Ag3PO4 s 1 2 1 2 1 2 4.3 ACIDS, BASES, AND NEUTRALIZATION | REACTIONS Many acids and bases are industrial and household substances (ǡ FIGURE 4.5), and some are important components of biological fluids. Hydrochloric acid, for example, is an important industrial chemical and the main constituent of gastric juice in your ACIDS stomach. Acids and bases are also common electrolytes. Hydrochloric acid, HCl Acetic acid (CH3COOH) is the primary component in vinegar and is a Acids As noted in Section 2.8, acids are substances that ionize in aqueous solution to form hy- monoprotic acid. drogen ions H+ aq . Because a hydrogen atom consists of a proton and an electron, H+ H is simply a proton. Thus, acids are often called proton donors. Molecular models of three common acids are1 shown2 in ǡ FIGURE 4.6. It has four hydrogens but only one of them, the H in the COOH group, is Protons in aqueous solution are solvated by water molecules, just as other cations ionized in water. The three other hydrogens are bound to carbon and do Cl are [Figure 4.3(a)]. In writing chemical equations involving protons in water, therefore, we write H+ aq . not break their C-H bonds in water. N Molecules of different acids ionize to form different numbers ofH+ ions. Both HCl Nitric acid, HNO 1 2 + 3 and HNO3 are monoprotic acids, yielding one H per molecule of acid. Sulfuric acid, + O H2SO4,is a diprotic acid, one that yields two H per molecule of acid. The ionization of H2SO4 and other diprotic acids occurs in two steps: + - + - C H2SO4 aq ¡ H aq + HSO4 aq [4.9] CH3COOH (aq) ⟶ H (aq) + CH3COO (aq) - + 2- HSO4 1 aq2 ∆ H 1 aq2 + SO4 1aq2 [4.10] Although H2SO4 is a strong1 electrolyte,2 1 only2 the first ionization1 2 (Equation 4.9) is complete. Thus, aqueous solutions of sulfuric acid contain a mixture ofH+ aq , - 2- HSO4 aq , and SO4 aq . Acetic acid, CH3COOH 1 2 The molecule CH3COOH (acetic acid) that we have mentioned frequently is the primary1 component2 in vinegar.1 2 Acetic acid has four hydrogens, as Figure 4.6 shows, but į FIGURE 4.6 Molecular models of three common acids. only one of them, the H in the COOH group, is ionized in water. The three other hydrogens are bound to carbon and do not break their C ¬ H bonds in water. BASES Bases are substances that accept H+ ions. Bases produce hydroxide ions OH- (aq) when they dissolve in water.

Ionic hydroxide compounds, such as NaOH, KOH, and Ca(OH)2, are among the most common bases. When dissolved in water, they release OH- ions into the solution.

Compounds that do not contain OH- ions can also be bases. For example, + ammonia (NH3) is a common base. When added to water, it accepts an H ion from a waterSECTION 4.3moleculeAcids, Bases, and andthereby Neutralization produces Reactions an OH125- ion.

GIVE IT SOME THOUGHT The structural formula of citric acid, a main component of citrus ϩϩ fruits, is H ϩ Ϫ H2O NH3 NH4 OH H C COOH į FIGURE 4.7 Hydrogen+ ion transfer. - NH3 (aq) + H2O ⟶ NH4 (aq) + OH (aq) HO C COOH An H2O molecule acts as a proton donor (acid), and NH3 acts as a proton acceptor H C COOH (base). Only a fraction of the NH3 molecules react with H2O. Consequently, NH3 is a H weak electrolyte. How many H+(aq) can be generated by each citric acid molecule dissolved in water?

Bases Bases are substances that accept (react with) H+ ions. Bases produce hydroxide ions OH- when they dissolve in water. Ionic hydroxide compounds, such as NaOH, KOH, and Ca(OH)2,are among the most common bases.When dissolved in water,they disso- ciate1 into2 ions, introducing OH- ions into the solution. Compounds that do not contain OH- ions can also be bases. For example, ammo- + nia (NH3) is a common base. When added to water, it accepts an H ion from a water molecule and thereby produces an OH- ion (Ǡ FIGURE 4.7): + - NH3 aq + H2O l ∆ NH4 aq + OH aq [4.11] Ammonia is a weak electrolyte because only about 1% of the NH forms NH + and 1 2 1 2 1 2 1 32 4 OH- ions. Strong and Weak Acids and Bases Acids and bases that are strong electrolytes (completely ionized in solution) are strong acids and strong bases.Those that are weak electrolytes (partly ionized) are weak acids and weak bases.When reactivity depends only on H+ aq concentration,strong acids are more reactive than weak acids. The reactivity of an acid, however, can depend on the anion as well as on H+ aq concentration. For example,1 hydrofluoric2 acid (HF) is a weak acid (only partly ionized in aqueous solution), but it is very reactive and vigor- ously attacks many substances,1 including2 glass. This reactivity is due to the combined action ofH+ aq and F- aq . Ĭ TABLE 4.2 lists the strong acids and bases we are most likely to encounter. You need to commit1 2this information1 2 to memory in order to correctly identify strong electrolytes and write net ionic equations. The brevity of this list tells us that most acids are weak. (For H2SO4,as we noted earlier,only the first proton completely ionizes.) The only common strong bases are the common soluble metal hydroxides. Most other metal hydroxides are insoluble in water. The most common weak base is NH3,which reacts with water to form OH- ions (Equation 4.11).

TABLE 4.2 • Common Strong Acids and Bases

Strong Acids Strong Bases

Hydrochloric, HCl Group 1A metal hydroxides [LiOH, NaOH, KOH, RbOH, CsOH] Hydrobromic, HBr Heavy group 2A metal hydroxides [Ca(OH)2,Sr(OH)2,Ba(OH)2] Hydroiodic, HI Chloric, HClO3 Perchloric, HClO4 Nitric, HNO3 Sulfuric, H2SO4 Strong and Weak Acids and Bases Acids and bases that are strong electrolytes (completely ionized in solution) are strong acids and strong bases. Those that are weak electrolytes (partly ionized) are weak acids and weak bases.

Common strong acids and bases Strong Acids Strong Bases Hydrochloric, HCl Group 1A metal hydroxides [LiOH, NaOH, KOH, RbOH, CsOH]

Hydrobromic, HBr Group 2A metal hydroxides [Ca(OH)2, Sr(OH)2, Ba(OH)2] Hydroiodic, HI

Chloric, HClO3

Perchloric, HClO4

Nitric, HNO3

Sulfuric, H2SO4

The brevity of this list tells that most acids are weak. (For H2SO4 only the ﬁrst proton completely ionizes). The common strong bases are the common soluble metal hydroxides. Most other metal hydroxides are insoluble in water. - The most common weak base is NH3, which reacts with water to form OH ions. 126126126 CHAPTERCHAPTERCHAPTER 4 4 Reactions4 ReactionsReactions in in Aqueous inAqueous Aqueous Solution Solution Solution

Strong and Weak AcidsGIVEGIVEGIVE IT IT IT SOME SOME SOMEand THOUGHTTHOUGHT THOUGHT Bases WhyWhyWhy isn’t isn’t isn’t Al(OH) Al(OH) Al(OH)3 3classifiedclassified3 classified as as aas a strong stronga strong base? base? base?

PRACTICE EXERCISE (ComparingSAMPLESAMPLESAMPLE Acid EXERCISE EXERCISE EXERCISEStrengths) 4.5 4.5 4.5ComparingComparing Comparing Acid Acid Acid Strengths Strengths Strengths TheTheThe following following following diagrams diagrams diagrams represent represent represent aqueous aqueous aqueous solutions solutions solutions of of acidsof acids acids HX, HX, HX, HY, HY, HY, and and and HZ,HZ, HZ, with with with waterwater water • The following diagrams representmoleculesmoleculesmolecules omittedaqueous omitted omitted for for clarity.for clarity. clarity.solutions Rank Rank Rank the the theacids acids acids of from from fromacids strongest strongest strongest HX, to to weakest. toweakest. weakest.HY, and HZ. Rank the acids from strongest to weakest. HXHXHX HY HY HY HZ HZ HZ HX HY HZ ؉؉؉ ؊؊؊ ؉؉؉ ؊؊؊ ؊؊؊ ؊؊؊ ؉؉؉ ؉؉؉ ؉؉؉ ؉؉ ؉؉؉ ؊؊؊ ؉ ؊؊؊ ؊؊؊ ؊؊؊ ؉؉؉؊؊؊ ؊؊؊ ؉؉؉ ؉؉؉ ؊؊؊؉؉؉ ؊؊؊ ؉؉؉ ؊؊؊ ؉؉؉ Solution SOLUTIONSOLUTIONSOLUTION We can determine the relative numbersAnalyzeAnalyzeAnalyze WeofWe Weare unchargedare are asked asked asked to to rank to rank rank three threemolecular three acids acids acids from from from strongest strongest strongestspecies to to weakest,to weakest, weakest,in the based based based ondiagrams. on on schematic schematic schematic The strongest acid is the one with the most H+ ions and fewest drawingsundissociateddrawingsdrawings of of their of their their solutions. solutions. solutions. molecules in solution. The weakest acid is the one with the largest PlanPlanPlanWeWe canWe can candetermine determine determine the the therelative relative relative numbers numbers numbers of of unchargedof uncharged uncharged molecular molecular molecular species species species in in theinthe the diagrams. diagrams. diagrams. number of undissociated molecules.TheThe The strongest strongest strongest acid acid acid is is the isthe theone one one with with with the the themost most most H H+ +H ions ions+ ions and and and fewest fewest fewest undissociated undissociated undissociated moleculesmolecules molecules inin in solution.solution.solution. The The The weakest weakest weakest acid acid acid is is the theis theone one one with with with the the thelargest largest largest number number number of of undissociatedof undissociated undissociated molecules. molecules. molecules. SolveSolveSolveTheTheThe order order order is is HY HYis HY77HZ7HZHZ77HX7HXHX . HY. HY . HYis is a aisstrong strong a strong acid acid acid because because because it it is isit totally totallyis totally ionized ionized ionized (no (no (no HY HY HY The order is HY > HZ > HX. moleculesmoleculesmolecules in in solution), insolution), solution), whereas whereas whereas both both both HX HX HX and and and HZ HZ HZ are are areweak weak weak acids, acids, acids, whose whose whose solutions solutions solutions consist consist consist of of aof a a mixturemixturemixture of of molecules of molecules molecules and and and ions. ions. ions. Because Because Because HZ HZ HZ contains contains contains more more more H H+ +H ions ions+ ions and and and fewer fewer fewer molecules molecules molecules than than than HY is a strong acid because it isHX, HX,totallyHX, it itis isita isastronger strongera ionizedstronger acid. acid. acid. (no HY molecules in solution), whereas both HX and HZ are weak acids, whose solutions consist of a mixture of molecules and ions. Because HZ contains more H+ ions and fewer PRACTICEPRACTICEPRACTICE EXERCISE EXERCISE EXERCISE molecules than HX, it is a strongerImagineImagineImagine acid. a diagrama diagram a diagram showing showing showing 10 10 Na 10 Na +Na+ ions ions+ ions and and and 10 10 OH10 OH OH-- ions.If ions.If- ions.If this this this solution solution solution were were were mixed mixed mixed with with with the the the oneone onepictured pictured pictured above above above for for forHY, HY, HY, what what what species species species would would would be be presentbe present present in in a ina diagram diagrama diagram that that that representsrepresents represents thethe the combinedcombinedcombined solutions solutions solutions after after after any any anypossible possible possible reaction? reaction? reaction? ++ + ------Answer:Answer:Answer:TheTheThe diagram diagram diagram would would would show show show 10 10 Na10 Na Na ions, ions, ions, 2 2OH OH 2 OH ions, ions, ions, 8 8Y Y 8 Y ions, ions, ions, and and and 8 8 H H82 2OHO 2molecules. Omolecules. molecules. • Imagine a diagram showing 10 Na+ ions and 10 OH- ions. If this solution were mixed with the one pictured above for HY, what species IdentifyingwouldIdentifyingIdentifying be presentStrong Strong Strong and and inand aWeak Weak diagramWeak Electrolytes Electrolytes Electrolytes that represents the combined solutions after any possible reaction? IfIf weIf we remember we remember remember the the thecommon common common strong strong strong acids acids acids and and and bases bases bases (Table (Table (Table 4.2) 4.2) 4.2) and and and also also also remember remember remember that that that NHNHNH3 is3 is 3a isaweak weaka weak base, base, base, we we can we can can make make make reasonable reasonable reasonable predictions predictions predictions about about about the the the electrolytic electrolytic electrolytic strength strength strength of of of a agreat greata great number number number of of water-solubleofwater-solublewater-solublesubstances.substances.substances.ĬĬTABLEĬTABLETABLE 4.3 4.3 4.3summarizessummarizessummarizes our our our observations observations observations aboutaboutabout electrolytes. electrolytes. +electrolytes. To To classify To classify classify- a asoluble solublea soluble substance substance -substance as as strong asstrong strong electrolyte, electrolyte, electrolyte, weak weak weak electrolyte, electrolyte, electrolyte, Answer: The diagram would show10Naoror nonelectrolyte,or nonelectrolyte, nonelectrolyte,ions, we we2OH wework work work our ourions, our way way way down down8Y down and andions and across across across and this this this table. 8table. table.H We2 WeO We first first molecules.first ask ask ask whether whether whether thethe the substancesubstancesubstance is is ionic isionic ionic or or molecular. or molecular. molecular. If If it If it is is it ionic, isionic, ionic, it it is is it a isa strong stronga strong electrolyte. electrolyte. electrolyte. The The The second second second column column column ofof Tableof Table Table 4.3 4.3 4.3 tells tells tells us us thatus that that all all ionicall ionic ionic compounds compounds compounds are are are strong strong strong electrolytes. electrolytes. electrolytes. If If the If the the substance substance substance isis is molecular,molecular,molecular, we we ask we ask askwhether whether whether it it is itis an isan acidan acid acid or or aor a base. base.a base. (It (It (Itis is an isan anacid acid acid if if it itif either either it either has has has H H first Hfirst first in in the inthe the chemicalchemicalchemical formula formula formula or or containsor contains contains a aCOOH COOHa COOH group.) group.) group.) If If it If it is itis an isan anacid, acid, acid, we we weuse use use Table Table Table 4.2 4.2 4.2 to to deter- todeter- deter- mineminemine whether whether whether it it is itis a is astrong stronga strong or or weakor weak weak electrolyte: electrolyte: electrolyte: All All Allstrong strong strong acids acids acids are are are strong strong strong electrolytes,electrolytes, electrolytes, andandand all all weakall weak weak acids acids acids are are areweak weak weak electrolytes. electrolytes. electrolytes. If If an Ifan acid an acid acid is is not isnot not listed listed listed in in Tablein Table Table 4.2, 4.2, 4.2, it it is is it probably isprobably probably a aweak weaka weak acid acid acid and and and therefore therefore therefore a aweak weaka weak electrolyte. electrolyte. electrolyte.

TABLETABLETABLE 4.3 4.3 4.3••Summary•SummarySummary of of theof the the Electrolytic Electrolytic Electrolytic Behavior Behavior Behavior of of Commonof Common Common SolubleSolubleSoluble Ionic Ionic Ionic and and and Molecular Molecular Molecular Compounds Compounds Compounds

StrongStrongStrong Electrolyte Electrolyte Electrolyte WeakWeakWeak Electrolyte Electrolyte Electrolyte NonelectrolyteNonelectrolyteNonelectrolyte

IonicIonicIonic AllAllAll NoneNoneNone NoneNoneNone MolecularMolecularMolecularStrongStrongStrong acids acids acids (see (see (see Table Table Table 4.2) 4.2) 4.2) WeakWeakWeak acids, acids, acids, weak weak weak bases bases bases AllAll Allother other other compounds compounds compounds Identifying Strong and Weak Electrolytes

It is possible to make predictions about the electrolytic strength of a great number of water-soluble substances. To classify a soluble substance as strong electrolyte, weak electrolyte, or non-electrolyte, we work our way down and across this table. We ﬁrst ask whether the substance is ionic or molecular. If it is ionic, it is a strong electrolyte.

Summary of the Electrolytic Behavior of Common Soluble Compounds Strong Electrolyte Weak Electrolyte Nonelectrolyte Ionic All None None Molecular Strong acids (see table) Weak acids, weak bases All other compounds Identifying Strong and Weak Electrolytes PRACTICE EXERCISE (Identifying Strong, Weak, and Non-electrolytes)

• Classify these dissolved substances as strong, weak, or non-electrolyte: CaCl2, HNO3, C 2H5OH (ethanol), HCOOH (formic acid), KOH.

Solution We can predict whether a substance is ionic or molecular based on its composition.

Two compounds are ionic: CaCl2 and KOH. Because the “Summary of the Electrolytic Behavior of Common Soluble Compounds“ table tells us that all ionic compounds are strong electrolytes, that is how we classify these two substances. The three remaining compounds are molecular. HNO3 and HCOOH are acids. Nitric acid, HNO3, is a common strong acid (“Common Strong Acids and Bases” table), and therefore is a strong electrolyte. Because most acids are weak acids, the best guess would be that HCOOH is a weak acid (weak electrolyte).

The remaining molecular compound, C2H5OH, is neither an acid nor a base, so it is a non-electrolyte.

Note: Although C2H5OH has an OH group, it is not a metal hydroxide and so not a base. Rather, it is a member of a class of organic compounds that have C-OH bonds, which are known as alcohols. Neutralization Reactions and Salts The properties of acidic solutions are quite different from those of basic solutions. Acids have a sour taste, whereas bases have a bitter taste. In addition, acidic and basic solutions differ in chemical properties in several other important ways.

When an acid and a base are mixed, a neutralization reaction occurs. The products of the reaction have none of the characteristic properties of either the acidic solution or the basic solution. E.g. When hydrochloric acid is mixed with a solution of sodium hydroxide, the reaction is

HCl (aq) + NaOH (aq) ⟶ H2O (l) + NaCl (aq) acid base water salt

Water and table salt, NaCl, are the products of the reaction. By analogy to this reaction, the term salt has come to mean any ionic compound whose cation comes from a base (for example, Na+ from NaOH) and whose anion comes from an acid (for example, Cl- from HCl). In general, a neutralization reaction between an acid and a metal hydroxide produces water and a salt. Neutralization Reactions and Salts PRACTICE EXERCISE (Writing Chemical Equations for a Neutralization Reaction)

• For the reaction between aqueous solutions of acetic acid (CH3COOH) and barium hydroxide, Ba(OH)2, write the balanced molecular equation

Solution Neutralization reactions form two products: H2O and a salt. We examine the cation of the base and the anion of the acid to determine the composition of the salt.

2+ - The salt contains the cation of the base (Ba ) and the anion of the acid (CH3COO ). Thus, the salt formula is Ba(CH3COO)2. This compound is soluble in water. The unbalanced molecular equation for the neutralization reaction is

CH3COOH (aq) + Ba(OH)2 (aq) ⟶ H2O (l) + Ba(CH3COO)2 (aq)

To balance this equation, we must provide two molecules of CH COOH to furnish the two CH COO- ions and to supply the two H ions needed to combine with the two OH ions of the base. The balanced molecular equation is

2 CH3COOH (aq) + Ba(OH)2 (aq) ⟶ 2 H2O (l) + Ba(CH3COO)2 (aq)

• For the reaction of phosphorous acid (H3PO3) and potassium hydroxide (KOH), write the balanced molecular equation.

Answers: (a)H3PO3 (aq) + 3 KOH (aq) ⟶ 3 H2O (l) + K3PO3 (aq)