Reactions involving Acids, Bases, & Salts CHAPTER 10 Reactions involving Acids, Bases, & Salts

Properties of Aqueous Solutions of Acids Acidic properties taste sour change the colors of indicators turn litmus red react with metals to generate H2(g) react with metal oxides and hydroxides to form salts and water aqueous solutions conduct electricity

Properties of Aqueous Solutions of Bases Basic properties taste bitter feel slippery change colors of indicators turn litmus blue react with acids to form salts and water aqueous solutions conduct electricity

Arrhenius Theory Svante Augustus Arrhenius - 1884 acids are anything that generate H+ in aqueous solutions, while bases produce OH- in aqueous solutions

Arrhenius Theory neutralization - combination of H+ (or H3O+) with OH- strong acids - ionize 100% in water HCl, HBr, HI, H2SO4, HNO3, HClO4, HClO3 strong bases - ionize 100% in water LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2 Can also happen with weak acids and/or weak bases 5 6

Arrhenius Theory net ionic equation for strong acid with strong base total ionic equation for strong acid with strong base net ionic equation for strong acid with strong base 6 7

Bronsted-Lowry Acid-Base Theory acids - proton (H+) donor bases - proton (H+) acceptor 8 9

acid-base reactions are proton transfer reactions note that we are often making coordinate covalent bonds differences between Arrhenius & Bronsted-Lowry theories reaction does not have to occur in an aqueous solution bases do not have to be hydroxides ~ ammonia is not a hydroxide 9 10

Bronsted-Lowry Acid-Base Theory weak acids have strong conjugate bases weak bases have strong conjugate acids primary reason they are weak acids or bases: strong conjugates recombine to form the original species Water is water can be either an acid or base in Bronsted-Lowry theory It is both amphiprotic and amphoteric amphiprotic ~ can donate or accept a proton amphoteric ~ a substance that can be either an acid or a base. 12 13

Amines amines are weak bases that behave like ammonia amines have organic groups attached to -NH2 group 14 15

HF>>HCl>HBr>HI HF<<HCl<HBr<HI Strengths of Acids Binary Acids acid strength increases with decreasing bond strength (inversely proportional) Strongest bond = weakest acid hydrogen halides bond strength HF>>HCl>HBr>HI acid strength HF<<HCl<HBr<HI 16 17

H2O>> H2S> H2Se> H2Te H2O<< H2S< H2Se< H2Te Strengths of Acids VIA hydrides bond strength H2O>> H2S> H2Se> H2Te acid strength H2O<< H2S< H2Se< H2Te 17 18

Strengths of Acids acid leveling strongest acid that can exist in water is H3O+ acids that are stronger than H3O+ merely react with water to produce H3O+ consequently all strong soluble acids have the same strength in water can only distinguish acid strength differences of strong acids in nonaqueous solutions like acetic acid

Strengths of Acids strongest acid in water is H3O+ HCl + H2O ® H3O+ + Cl- HCl is so strong it forces water to accept H+ strongest base in water is OH- NH2- + H2O ® NH3 + OH- NH2- is strong enough to remove H+ from water Why? Water is amphiprotic 21 22

Strengths of Acids Acid Conjugate Base Strongest acid Weakest base HClO4 ClO4- H+(H3O+) H2O CH3CO2H « CH3CO2- H2O OH- NH3 NH2- Weakest acid Strongest base 20 21

Strengths of Acids ternary acids /oxyacids – acids containing H, O, and another element (usually a nonmetal) ternary acid strength usually increases with increasing number of O atoms on central atom increasing oxidation state of central atom acids having same central atom, highest oxidation state of central atom is usually strongest acid HClO < HClO2 < HClO3 < HClO4 weakest strongest 24 25

HNO2<HNO3 H2SO3< H2SO4 HNO2>HNO3 H2SO3> H2SO4 Strengths of Acids weak ternary acids have stronger H-O bonds than stronger ternary acids acid strength HNO2<HNO3 H2SO3< H2SO4 H-O bond strength HNO2>HNO3 H2SO3> H2SO4 23 24

Lewis Acid-Base Theory acid – an electron pair acceptor base – an electron pair donor neutralization - coordinate covalent bond formation 47 48

~ ionization of ammonia in more detail ~ ionization of HBr HBr + H2O ® H3O+ + Br- acid base in more detail 48 49

Lewis Theory sodium fluoride + boron trifluoride ammonia + HBr Lewis acid-base reaction but not Arrhenius or Bronsted-Lowry NaF + BF3 ® Na+ + BF4- ammonia + HBr Lewis and Bronsted-Lowry acid base reaction but not Arrhenius NH3 + HBr ® NH4+ + Br- 50 51

Acidic, Basic, and Neutral Salts A salt is an ionic compound that contains at least one spectator ion. The salt therefore dissociates completely in water Neutral salts – normal salts: contain no ionizible H atoms or OH groups. These salts have no effect on the pH of a solution. Normally formed between the reaction of a strong acid and strong base. Most alkali and alkaline earth binaries are neutral salts. Ex. NaCl, KI, LiNO3, MgBr2

Some salts will produce an acidic or basic solution when added to water. Acidic salts are ionic compounds that can provide an H+ to a solution; does not necessarily produce acidic solns. These compounds are able to neutralize bases. Normally formed from the reaction of a strong acid and weak base. Ex. NH4I , KH2 AsO4, K2 HPO4, NaHSO4 , NaHCO3 NH4 I + H2O  H3O+ + NH3 + I-

Basic salts are ionic compounds that increase the OH- concentration Basic salts are ionic compounds that increase the OH- concentration. If the compound has an anion that would make a weak acid then it’s a basic salt. Can contain unreacted OH group that can neutralize acids even though they are not necessarily basic. Most transition metal binary compounds in water make basic salts. Basic salts tend to be insoluble. Can also be formed from the reaction of a strong base and a weak acid. Ex. Al(OH)2 Cl, Fe(OH)2 and some anions to look for F-, CN- , CNS- , H- NaF + H2O  Na+ + OH- + HF Li2C2O4 + H2O  H2C2O4 + Li+ + OH-

One method of increasing the solubility and the absorption of a medication is to convert weakly acidic drugs into sodium salts before making the pills that will be ingested. How does this preparation method enhance the drug’s solubility in the stomach? (hint: stomach acid is about 1M HCl) Medicines that are weakly basic are not absorbed well into the bloodstream. One method to increase their absorption is to take an antacid at the same time that the medicine is administered. How does this method increase the absorption?