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 hy- 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. 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 hydro- gens 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 shownconstituent in ǡ FIGURE of gastric 4.6 . juice in your stomach. Acids and bases are also commonProtons electrolytes.