Grossmont College Chemistry 142 Laboratory ManualLehman, Maley, and Oakes 4thEditionChemistry 142 Laboratory ManualCompiled by Jeff Lehman, John Maley, and John Oakes1Grossmont College8800 Grossmont College Dr.El Cajon, CA 92020 Prepared for printing on July 26, 20021. Original material by, Bill Bornhorst, Bill Givens, Jeff Lehman, John Maley, John Oakes, andChuck ParkChemistry 142 Grossmont College1ContentsEXPERIMENT 1 Determination of Ka , Kb , and % Ionization from pH 5Background 5Procedure 7EXPERIMENT 2 pH Indicators 11Discussion 11Determination of the Ka of an Indicator 12Calculations and Results 14EXPERIMENT 3 Solubility Product and Le Châtelier’s Principle 15Introduction 15Procedure 17Calculations 17Questions 17Pre-Laboratory Questions 17EXPERIMENT 4 Titration Curves 19Objective 19Procedure 19Data Analysis 21Contents2Chemistry 142 Grossmont CollegeEXPERIMENT 5 The Kinetics of the Dissociation of Hydrogen Peroxide 23Theory 23The Experiment 25Calculations 27Questions 28EXPERIMENT 6 A Kinetic Study of the Oxidation of an Alcohol by Dichromate Ion 29Introduction to Kinetics 29Spectrophotometry 31Purpose 31Background 31Procedure 32Calculations 33Sample Notebook Page 33Post-Laboratory Questions 34EXPERIMENT 7 Electrochemistry 35Objective 35Galvanic (Voltaic) Cells 35Electrolytic Cells 39Concentration Cells 41Questions and Data Interpretation 43EXPERIMENT 8 Electrochemical Cells (B) 53Procedure 53EXPERIMENT 9 Corrosion 55Objectives 55Introduction 55Procedure 56Data 58Post Laboratory Questions 59EXPERIMENT 10 Analysis of a Cation Mixture 61Objective 61Introduction 61Chemistry 142 Grossmont College3ContentsGeneral Techniques 63Experimental Procedure 63Observations and Data 66Questions 67EXPERIMENT 11 Group I Cations: The Silver Group 69Introduction 69Experimental Procedure: Analytical Group I 71Data and Calculation s72Questions 72EXPERIMENT 12 Cation Group II: The Acid-Insoluble Sulfides 73Introduction 73Procedure 76Questions 78EXPERIMENT 13 Cation Group III: The Basic Insoluble Sulfides 81Background 81Procedure 84Questions 85EXPERIMENT 14 Anion Analysis 87Background 87Experimental Procedure - Preliminary Tests 89Experimental Procedure - Specific Tests 90Questions 91EXPERIMENT 15 Five Solution Analysis 93Background 93EXPERIMENT 16 Determining the Identity of an Unknown Solution 97Introduction 97Prelaboratory Questions 98Procedure 98Post-Laboratory Question 99Contents4Chemistry 142 Grossmont CollegeEXPERIMENT 17 Ligand Substitution 101Objective 101Introduction 101Procedure 103Data Treatment 105Prelaboratory Exercise 106EXPERIMENT 18 First-Order Radioactive Decay 107Introduction 107The Experiment 108Results 108Questions 108EXPERIMENT 19 Synthesis of Aspirin 111Objective 111Discussion 111Procedure 112Index 115Chemistry 142 Grossmont College1–5EXPERIMENT 1Determination of Ka , Kb , and % Ionization from pHBackgroundLike many substances acids and bases were first defined phenomenologically. That is, chemists defined them according to their chemical behavior. For instance, acids were those substances that tasted sour, reacted with certain metals to produce hydrogen gas, and caused a color change in cer-tain indicator solutions. Bases, were those substances that tasted bitter, turned certain indicator solutions a certain color, and felt slippery. As time has progressed chemists have devised more fun-damental definitions of acids and bases.There are a number of different definitions of acids and bases which are useful to chemists. One example is the Arrhenius defintion. In this definition acids are those substances that increase the concentration hydrogen ion in solution and bases are those substances that increase the concentra-tion of hydroxide ion in solution.A broader definition was developed by the Danish chemist Johannes Brønsted and the English chemist Thomas Lowry. Their definitions followBrønsted-Lowry Acid. A substance that can donate a protonHA(aq) + H2O A–(aq) + H3O+(aq)(EQ 1.1)Brønsted-Lowry Base. A substance that can accept a protonB(aq) + H2O BH+(aq) + OH–(aq)(EQ 1.2)Acid and base molecules and ions that differ only by the addition or removal of a proton are called conjugate pairs. For example HA/A– and B/BH+ both represent conjugate acid-base pairs. It may be shown that the Ka of an acid times the Kb of its conjugate base are equal to Kw (See section 15.13 in McMurry and Fay for derivation). Therefore for the acid HA, the Kb of its conjugate base, A–, is Kw/Ka where Kw = 1.0 ×10–14 = [H3O+][OH–].Determination of Ka , Kb , and % Ionization from pH1–6Chemistry 142 Grossmont CollegeStrong Acids and BasesAcids and bases which are essentially 100\% dissociated in water are said to be strong. The com-mon strong acids and bases are listed in Table 1.1 Calculating Ka and Kb The dissociation constants for the strong acids and bases are undefined because the concentration of the undissociated form is essentially zero, which would result in a value of infinity.Numerical values of the dissociation constants for weak acids and bases may be determined by measuring the pH of the solution. For a weak acid, the hydronium ion concentration,[H3O+], is approximately equal to the concentration of the conjugate base [A–] as shown below: If the pH is observed to be 3.20 then,(EQ 1.3)Substituting the equilibrium values from above into the Ka expression yields a numerical value for Ka.(EQ 1.4)We can also use the expression given above for the relationship of Kb to Ka.(EQ 1.5)TABLE 1.1Strong Acids and BasesStrong Acids Strong Baseshydrochloric acid (HCl) sodium hydroxide (NaOH)hydrobromic acid (HBr) potassium hydroxide (KOH)hydroiodic acid (HI)barium hydroxide (Ba(OH)2)nitric acid (HNO3) calcium hydroxide (Ca(OH)2)sulfuric acid (H2SO4)perchloric acid (HClO4)chloric acid (HClO3)HA +H2OA–+H3O+I0.10 M55 M010–7 M∆–x–x+x+xE0.10–x55x10–7– xH+[] 103.20–M 6.314–×10 Mx== =Kax[]x[]0.10 x–()------------------------6.314–×10()2(0.10 6.314–×10 )–----------------------------------------------4.06–×10== =Kb for A_KwKa-------1.014–×104.06–×10----------------------- 2 . 59–×10== =Chemistry 142 Grossmont College1–7ProcedureIf the pH reading is greater than 7 the solution is basic and the [OH–] will be used to calculate Kb.If the pH is observed to be 11.45 then the [OH–] = 10–pOH = 10–2.55 and,(EQ 1.6)Within what pH range can you prudently neglect the molarities of the ions in deionized water when added to dissociation