AP Chemistry: Acids & Bases Notes Objectives Definition of Acids-Bases Acid Strength Base Strength ph-poh Scale Calculating ph of Strong Acids-Bases Calculating ph of Weak Acids-Bases Calculating Ka from percent dissociation Polyprotic Acids Acid-Base Properties of Salts Calculating with salts Effect of Structure on Acid-Base Properties Acid-Base Properties of Oxides Definition of Acids-Bases Properties of Acids-Bases Acids Bases Arrhenius Acid Base Bronsted-Lowry Acid Base - 1 -
Lewis Acid Base Acid-Base Definition Summary Table Model Definition of Acid Definition of Base Arrhenius H + producer OH - producer Bronsted-Lowry H + donor H + acceptor Lewis Electron pair acceptor Electron pair donor Conjugate Acid-Base Concept Acid-Dissociation Constant Values of Ka for some Common Monoprotic Acids Forumla Name Value of Ka HSO4 - Hydrogen sulfate ion 1.2 10-2 HClO2 Chlorous acid 1.2 10-2 HC2H2ClO2 Monchloracetic acid 1.35 10-3 HF Hydrofluoric acid 7.2 10-4 HNO2 Nitrous acid 4.0 10-4 HC2H3O2 Acetic Acid 1.8 10-5 HOCl Hypochlorous acid 3.5 10-8 HCN Hydrocyanic Acid 6.2 10-10 NH4 + Ammonium Ion 5.6 10-10 HOC6H5 Phenol 1.6 10-10 - 2 -
Acid Strength Definitions: Strong Acid Weak Acid (Discuss Diagram) List of Strong Acids Base Strength Definitions: Strong Base Weak Base Amines List of Base Acids - 3 -
ph-poh Scale Autoionization of Water Definitions ph = poh = ph + poh = 10 -ph = 10 -ph = ph poh [H+] [OH - ] Acid-Base? 2.3 4.5 3.4x10-5 4.6 x 10-9 7-4 -
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Calculating ph of Strong Acids-Bases Sample Problems a. Calculate the ph of a 0.10 M HNO3 solution b. Calculate the ph of a 1 x 10-10 M HClO4 solution c. 54 ml of 0.00125-M HNO3 is mixed with 25.0-mL of 0.025-M HCl. What is the ph of the resulting solution? d. What is the ph of a 25.0 ml of a 0.25-M solution of NaOH - 6 -
Calculating ph of Weak Acids-Bases Sample Problems a. What is the ph of 25.0 ml of a 0.250-M solution of acetic acid? Values of Ka for some Common Monoprotic Acids Forumla Name Value of K a HSO4 - Hydrogen sulfate ion 1.2 10-2 HClO2 Chlorous acid 1.2 10-2 HC2H2ClO2 Monchloracetic acid 1.35 10-3 HF Hydrofluoric acid 7.2 10-4 HNO2 Nitrous acid 4.0 10-4 HC2H3O2 Acetic Acid 1.8 10-5 HOCl Hypochlorous acid 3.5 10-8 HCN Hydrocyanic Acid 6.2 10-10 NH4 + Ammonium Ion 5.6 10-10 HOC6H5 Phenol 1.6 10-10 b. What the percent dissociation of a 0.325-M solution of formic acid? c. Calculate the ph of a solution that contains 1.00 M HCN and 5.00 M HNO2. Also, calculate the concentration of CN - ion in this solution at equilibrium. - 7 -
d. What is the ph of a solution where 25.0-mL of 0.25 M HNO3 is mixed with 25.0- ml of 0.25-M HNO2 e. What is the ph of a 0.25-M solution of NH3? f. What is the ph of a mixture of 25.0 ml of 0.25M KOH and 25.0 ml of 0.25 M CH3NH2 Values of Kb for Some Common Weak Bases Name Formula Conjugate Kb Acid Ammonia NH3 NH4 + 1.8 x 10-5 Methylamine CH3NH2 CH3NH2 + 4.38 x 10-4 Ethylamine C2H5NH2 C2H5NH3 + 5.6 x 10-4 Diethylamine (C2H5)2NH2 (C2H5)2NH2 + 1.3 x 10-3 Triethylamine (C2H5)3N (C2H5)3NH + 4.0 x 10-4 Hydroxylamine NONH2 NONH3 + 1.1 x 10-8 Hydrazine H2NNH2 H2NNH3 + 3.0 x 10-6 Aniline C6H5NH2 C6H5NH3 + 3.8 x 10-10 Pyridine C5H5N C5H5NH + 1.7 x 10-9 - 8 -
Calculating Ka from percent dissociation Sample 1: Lactic Acid (HC 3H 5O 3) is a waste product that accumulates in muscle during exertion, leading to pain and a feeling of fatigue. In a 0.100 M aqueous solution, lactic acid is 3.7% dissociated. Calculate the value of Ka for this reaction. Polyprotic Acids Dissociation Constants for Polyprotic Acids Name Formula Ka1 Ka2 Ka3 Phosphoric Acid H3PO4 7.5 10-3 6.2 10-8 4.8 10-13 Arsenic Acid H3AsO4 5 10-3 8 10-8 6 10-10 Carbonic Acid H2CO3 4.3 10-7 5.6 10-11 Sulfuric Acid H2SO4 Large 1.2 10-2 Sulfurous Acid H2SO3 1.5 10-2 1.0 10-7 Oxalic Acid H2C2O4 6.5 10-2 6.1 10-5 Ascorbic Acid Vitamin C H2C6H6O6 7.9 10-5 1.6 10-12 Definition of Polyprotic Acids Monoprotic Definition and dissociation Diprotic Definition and dissociation Triprotic Definition and dissociation - 9 -
The Value of Ka1 vs Ka2 vs Ka3 Polyprotic Acid Problem 1 Calculate the ph and concentration of all species of a 3.0-M solution of phosphoric acid (H3PO4) - 10 -
Acid-Base Properties of Salts Salts that Produce Basic Solutions: Examples Salts of weak acids Ka x Kb = Kw Salts that Produces Acid Solutions: Examples Salts of weak bases Calculating with salts Sample 1: What is the ph of a 0.140 M solution of sodium acetate? - 11 -
Sample 2: What is the ph of a 0.140 M solution of diethyl amine? Sample 3: Predict whether an aqueous solution of each of the following salts will be basic, acidic, or neutral a. NH4C2H3O2 b. NH4CN c. Al2(SO4)3 ph of Solutions and Ka vs Kb Ka>Kb Kb>Ka Ka=Kb ph < 7 (acidic) ph >7 (basic) ph=7 (neutral) - 12 -
Effect of Structure on Acid-Base Properties Discussion of the polarity of the hydrogen halides Discussion of the Oxyacids Hydrogen Halide Acid Strength and Bond Strength H-X Bond Bond Strength (kj/mol) Acid Strength in Water H F 565 Weak H Cl 427 Strong H Br 363 Strong H I 295 Strong Oxyacids and their Ka Values Oxyacid Ka Value HCLO4 Large (10 10 7 ) HClO3 1 HClO2 1.2 10-2 HClO 3.5 10-8 H2SO4 Large H2SO3 1.5 10-2 HNO3 Large HNO2 4.0 10-4 - 13 -
Acid-Base Properties of Oxides Metal Oxides + Water Non-Metal Oxides + Water - 14 -