acids, bases, and salts

Acids, Bases, and SaltsCHM 1010 PGCC Barbara A. Gage

CHM 1010 PGCC Barbara A. Gage

Characteristics of Acids and BasesCHM 1010 PGCC Barbara A. Gage

Acid BaseLitmus colorPhenolphthalein colorpH rangeReaction with active metal (like Mg)TasteFormula component


AcidsStronghydrochloric acid, HClhydrobromic acid, HBrhydroiodic acid, HInitric acid, HNO3sulfuric acid, H2SO4perchloric acid, HClO4Weakhydrofluoric acid, HFphosphoric acid, H3PO4acetic acid, CH3COOH (or HC2H3O2)ionizes completely in waterionizes partially in watercarbonic acid, H2CO3CHM 1010 PGCC Barbara A. Gage


Figure 18.2The extent of dissociation for strong acids.H+ and H2O H3O+ (hydronium ion)CHM 1010 PGCC Barbara A. Gage


Figure 18.3The extent of dissociation for weak acids.CHM 1010 PGCC Barbara A. Gage


Bases (or alkalis)StrongWeaksodium hydroxide, NaOHcalcium hydroxide, Ca(OH)2potassium hydroxide, KOHstrontium hydroxide, Sr(OH)2barium hydroxide, Ba(OH)2ammonia, NH3 (NH4OH)ModerateDissociates completelyDissociates completely but is not very solublealuminum hydroxide, Al(OH)3magnesium hydroxide, Mg(OH)2Dissociates partiallycarbonates, CO32-bicarbonates, HCO31-CHM 1010 PGCC Barbara A. Gage


Figure 4.8An aqueous strong acid-strong base reaction on the atomic scale.MX is a salt an electrolyte that is not an acid or baseCHM 1010 PGCC Barbara A. Gage


Acid and Base DefinitionsArrheniusAcid = compound that forms hydrogen (H+) ions in waterBase = compound that forms hydroxide (OH-) ions in water



Acid and Base DefinitionsBronsted-LowryAcid = proton donor (H+ is a proton)Base = proton acceptor

An acid-base reaction can now be viewed from the standpoint of the reactants AND the products.An acid reactant will produce a base product and the two will constitute an acid-base conjugate pair.CHM 1010 PGCC Barbara A. Gage


Figure 18.8Proton transfer as the essential feature of a Brnsted-Lowry acid-base reaction.(acid, H+ donor)(base, H+ acceptor)(base, H+ acceptor)(acid, H+ donor)CHM 1010 PGCC Barbara A. Gage


Table 18.2 The Conjugate Pairs in Some Acid-Base ReactionsConjugate PairConjugate PairCHM 1010 PGCC Barbara A. Gage


SAMPLE PROBLEM 18.4Identifying Conjugate Acid-Base PairsSOLUTION:proton donorproton acceptorproton acceptorproton donorconjugate pair1conjugate pair2conjugate pair2conjugate pair1proton donorproton acceptorproton acceptorproton donorCHM 1010 PGCC Barbara A. Gage


Molecules as Lewis AcidsacidbaseadductAn acid is an electron-pair acceptor.A base is an electron-pair donor.M(H2O)42+(aq)adductCHM 1010 PGCC Barbara A. Gage


SAMPLE PROBLEM 18.12Identifying Lewis Acids and BasesSOLUTION:acceptordonordonoracceptoracceptordonorCHM 1010 PGCC Barbara A. Gage


Acid AnhydridesNon-metal oxides react with water to form acidic solutions

CO2 (g) + H2O (l) H2CO3 (aq)N2O5 (s) + H2O (l) 2 HNO3 (aq)SO3 (g) + H2O (l) H2SO4 (aq)

Dissolved non-metal oxides cause acid rain.CHM 1010 PGCC Barbara A. Gage


Basic AnhydridesMetal oxides react with water to form alkaline solutions

Na2O (s) + H2O (l) 2 NaOH (aq)CaO (s) + H2O (l) Ca(OH)2 (aq)Al2O3 (s) + 3 H2O (l) 2 Al(OH)3 (aq)

Lime (CaO) is used on lawns and is converted to Ca(OH)2 when it rains. CaO is less hazardous to handle.CHM 1010 PGCC Barbara A. Gage


Figure 4.7An acid-base titration.Start of titrationExcess of acidPoint of neutralizationSlight excess of baseCHM 1010 PGCC Barbara A. Gage


Sample Problem 4.5Finding the Concentration of Acid from an Acid-Base TitrationPLAN:SOLUTION:volume(L) of basemol of basemol of acidM of acidmultiply by M of basemolar ratiodivide by L of acid(33.87-0.55) mL x= 0.03332 L0.03332 LX 0.1524 M= 5.078x10-3 molNaOHMolar ratio is 1:1CHM 1010 PGCC Barbara A. Gage


Kc[H2O]2 =[H3O+][OH-]The Ion-Product Constant for WaterKw =A change in [H3O+] causes an inverse change in [OH-].= 1.0 x 10-14 at 250CIn an acidic solution, [H3O+] > [OH-]In a basic solution, [H3O+] < [OH-]In a neutral solution, [H3O+] = [OH-]CHM 1010 PGCC Barbara A. Gage


Figure 18.4The relationship between [H3O+] and [OH-] and the relative acidity of solutions.[H3O+][OH-]ACIDIC SOLUTIONBASIC SOLUTIONNEUTRAL SOLUTIONCHM 1010 PGCC Barbara A. Gage


SAMPLE PROBLEM 18.2Calculating [H3O+] and [OH-] in an Aqueous SolutionPROBLEM:A research chemist adds a measured amount of HCl gas to pure water at 250C and obtains a solution with [H3O+] = 3.0x10-4M. Calculate [OH-]. Is the solution neutral, acidic, or basic?SOLUTION:PLAN:Use the Kw at 250C and the [H3O+] to find the corresponding [OH-].Kw = 1.0x10-14 = [H3O+] [OH-] so [OH-] = Kw/ [H3O+] = 1.0x10-14/3.0x10-4 =3.3x10-11MCHM 1010 PGCC Barbara A. Gage


Figure 18.5The pH values of some familiar aqueous solutions.pH = -log [H3O+]CHM 1010 PGCC Barbara A. GagepOH = -log [OH-]pH + pOH = 14


Figure 18.6The relations among [H3O+], pH, [OH-], and pOH.CHM 1010 PGCC Barbara A. Gage


SAMPLE PROBLEM 18.3Calculating [H3O+], pH, [OH-], and pOHPROBLEM:In an art restoration project, a conservator prepares copper-plate etching solutions by diluting concentrated HNO3 to 2.0M, 0.30M, and 0.0063M HNO3. Calculate [H3O+], pH, [OH-], and pOH of the three solutions at 250C.SOLUTION:For 2.0M HNO3, [H3O+] = 2.0M and -log [H3O+] = -0.30 = pH[OH-] = Kw/ [H3O+] = 1.0x10-14/2.0 = 5.0x10-15M; pOH = 14.30[OH-] = Kw/ [H3O+] = 1.0x10-14/0.30 = 3.3x10-14M; pOH = 13.48For 0.3M HNO3, [H3O+] = 0.30M and -log [H3O+] = 0.52 = pH[OH-] = Kw/ [H3O+] = 1.0x10-14/6.3x10-3 = 1.6x10-12M; pOH = 11.80For 0.0063M HNO3, [H3O+] = 0.0063M and -log [H3O+] = 2.20 = pHCHM 1010 PGCC Barbara A. Gage


BuffersSolutions that resist change in pHCan maintain any pH value between 0 and 14 (not just neutral pH 7)Composed of a weak acid and a salt made from the weak acid or weak base and salt made from the weak baseExamples: HC2H3O2 and NaC2H3O2 NH4OH and NH4ClCHM 1010 PGCC Barbara A. Gage


BuffersReaction with acid:HC2H3O2 + C2H3O2- + H+ HC2H3O2 + HC2H3O2

Reaction with base:HC2H3O2 + C2H3O2- + OH- C2H3O2- + C2H3O2- + HOH

A buffer regenerates its own components. The pH it maintains depends on the ratio of salt to acid (or base) and the nature of the acid (or base).



acids, bases, and salts

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