Scruggs Chap 16a

Scruggs Chap 16a - Chapter 16 Acid-Base Equilibria q Acids...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Chapter 16 Acid-Base Equilibria q Acids and bases are found in many common substances and are important in life processes. Which of the following are acids and which are bases? q Oven Cleaner q Sodium Carbonate q Vinegar q Windex q Vitamin C (Ascorbic Acid) q Soap Chapter 16 Acid-Base Equilibria q There are many organic/biological acids and bases, and there are acids used industrially for many purposes. q Example: H2SO4 q Used in the production of fertilizers, paint dyes, plastics, pharmaceuticals, ... q The acid in lead storage batteries in most cars 16.1 Acids and Bases q Acid: Base: tastes sour tastes bitter stings skin feels slippery corrosive to metals releases CO2 from carbonates turns litmus red turns litmus blue turns phenolphthalein colorless turns ph.ind. pink Arrhenius Theory q Acid: substance that produces H+ in HCl aqueous solution q Base: substance that produces OH- in aqueous solution NaOH q Not realistic: H+ has a radius of 10-13 cm, which gives a very concentrated charge, so it associates with H2O as H(H2O)4+, which we usually simplify to H3O+ or H+ (aq) 16.2 Bronsted-Lowrey Acids and Bases q Acid: donates a proton to another substance q Base: accepts a proton from another substance q Acids: HCl(aq) + H2O(l) H3O+ (aq) + Cl-(aq) h NH4+(aq) + H2O(l) h H3O+ (aq) + NH3(aq) q Bases: h NH3(aq) + H2O(l) h OH-(aq) + NH4+ (aq) h CO32-(aq) + H2O(l) h OH-(aq) + HCO3-(aq) Bronsted-Lowrey Acids and Bases Transfer of a proton (hydrogen ion) Conjugate Acids and Bases q Pair of substances differing only by one H+ q HF(aq) + H2O(l) h H3O+ (aq) + F-(aq) acid base acid base q CO32- (aq) + H2O(l) h HCO3-(aq) + OH-(aq) Which of these is a correct pairing of an acid and its conjugate base (in that order)? 1. HCO3-, H2CO3 2. NH3, NH4+ 3. H3PO4, H2PO44. H2PO4-, H3PO4 0% 1 0% 2 0% 3 0% 4 Conjugate Acid-Base Pairs q Determine the formula of the conjugate acid of each base. Base Conjugate Acid Amphoprotism q Amphoprotic substances can act as either an acid or a base. q HCO3-(aq) + OH-(aq) h CO32-(aq) + H2O(l) q HCO3-(aq) + HCl (aq) h H2CO3(aq) + Cl-(aq) h 1 Amphoprotism q Write equations to describe the reactions of HPO42- with : q OHq HCl 1 Polyprotic Acids q Some acids can donate more than one proton. q Mono- di- tri- ... polyq Diprotic: H2SO4, H2CO3, H2SO3, q Not all H atoms are acidic. Example: acetic acid, CH3CO2H q In oxoacids, the acidic hydrogens are bonded to oxygen. 1 Polyprotic Acids q How many acidic hydrogens? H2SO4 H3PO4 CH3CH2CO2H 1 Acid Strengths q We can measure the relative tendency for acids to donate protons (usually relative to the solvent). Acids are rated from strong to weak. q Strong acid: Complete donation of proton to water Examples q HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq) q H2SO4(aq) + H2O(l) H3O+(aq) + HSO4-(aq) 1 Strong Acid: HNO3 q HNO3 is completely ionized into the ions H3O+ and NO3- 1 Acid Strengths In water: q Any acid that is stronger than H3O+ (the conjugate acid of the solvent) will ionize completely to form H3O+ q H3O+ is the strongest acid we can find in H2O 1 Acid Strengths q Weak acid: partial donation of protons to water. q HF(aq) + H2O(l) h H3O+(aq) + F-(aq) weaker weaker acid base stronger acid stronger base q The reaction reaches a state of equilibrium in which the relative acid strengths determine the degree of ionization. 1 Weak Acid: HF q HF is only partially dissociated into H3O+ and F- 1 1 Predicting Position of Equilibrium q All acids above H3O+ in the table are strong acids, which ionize completely in aqueous solution. q All bases below OH- in the table are strong bases, which react completely in aqueous solution. q The table can be used to make predictions: The stronger acid reacts with the stronger base to form a weaker acid and a weaker base. 2 Predicting Acid-Base Reactions q HCl + HSO3- h q stronger stronger acid base H2SO3 + Clweaker weaker acid base Which side is favored at equilibrium? 2 2 In the equilibrium given, will the product or reactant side be favored? F- + HSO4- HF + SO42- 91% 1. 2. 3. 4. Product Reactant Neither Can't Tell 1 6% 2 3% 3 0% 4 2 16.3 Autoionization of Water q Water undergoes autoionization: H2O + H2O h H3O+ + OHh K = [H O ][OH ] = 1.0 x 10 at 25oC q w 3 + -14 Called the ion product of water q Since [H2O] is constant, it is omitted 2 16.3 Autoionization of Water q Add an acid, [H3O+] > [OH-] q Example: q 0.10 M HCl (strong acid, completely ionized) [H3O+][OH-] = 1.0 x 10-14 (0.10)[OH-] = 1.0 x 10-14 [OH-] = 1.0 x 10-14 /0.10 = 1.0 x 10-13 M 2 Autoionization of Water q Add a base, [H3O+] < [OH-] q Example: 0.010 M NaOH (strong base, completely ionized) [H3O+][OH-] = 1.0 x 10-14 [H3O+](0.010) = 1.0 x 10-14 [H3O+] = 1.0 x 10-14 /0.010 = 1.0 x 10-12 M q Acidic Solution [H3O+] > 10-7 M 2 Find the [H3O+] for the solutions given below. Solution A: 1.3 x 10-2M HNO3 Solution B: 0.020M NaOH + 3 A + 3 B 86% 1. [H O ] =1.3x10-2M, [H O ] =2.0x10-2M 2. [H3O+]A=7.7x10-13M, [H3O+]B=2.0x10-2M 3. [H3O+]A=1.3x10-2M, [H3O+]B=5.0x10-13M 4. [H3O ]A=7.7x10 M, [H3O+]B=5.0x10-13M + -13 11% 3% 1 0% 2 3 4 2 16.4 The pH Scale q pH scale defined to make it easier to refer to relative [H3O+] or [OH-] values q pH = -log [H3O+] q pOH = -log [OH-] q [H3O+] = 1.0 M q [H3O+] = 1.0 x 10-14 M q [H3O+] = 1.0 x 10-7 M pH = 0 pH = 14 pH = 7 2 16.4 The pH Scale q pH scale is defined to make it easier to refer to relative [H3O+] or [OH-] values q pH = -log [H3O+] q pOH = -log [OH-] q [H3O+] = 1.0 M q [H3O+] = 1.0 x 10-14 M q [H3O+] = 1.0 x 10-7 M pH = 0 pH = 14 pH = 7 pOH= pOH= pOH= 2 16.4 The pH Scale q pH scale is defined to make it easier to refer to relative [H3O+] or [OH-] values q pH = -log [H3O+] q pOH = -log [OH-] q [H3O+] = 1.0 M q [H3O+] = 1.0 x 10-14 M q [H3O+] = 1.0 x 10-7 M pH = 0 pH = 14 pH = 7 pOH=14 pOH=0 pOH=7 3 pH Scale q pH + pOH = 14 = pKw q Neutral: pH=pOH = 7 q Acidic: pH < 7 pOH > 7 q Basic: pH > 7 pOH < 7 3 Fig. 16.5 3 16.5 Strong Acids and Bases Strong Acids q The strong common acids are HCl, HBr, HI, HNO , HClO , HClO , and H SO . 3 3 4 2 4 q Strong acids are strong electrolytes. q All strong acids ionize completely in 3 Strong Acids and Bases Strong Bases q Most ionic hydroxides are strong bases (e.g. NaOH, KOH, and Ca(OH)2). q Strong bases are strong electrolytes and dissociate completely in solution. q The pOH (and hence pH) of a strong base is obtained from the initial molarity of the base. Be careful of stoichiometry. 3 What are the pH and pOH of the following solutions? 1. A: pH=2, pOH=12; B: pH=9, pOH=5 Solution A: 0.20 M HCl 2. A:pH=0.7, pOH=13.3; B:pH=12.7, pOH=1.3 3. A:pH=0.7,pOH=13.3; B:pH=1.3,pOH=12.7 Solution B: 0.050 M NaOH 0% 1 0% 2 0% 3 3 pH Calcs q When we substitute [HCl] for [H3O+], we assume that: [H3O+] from HCl >> [H3O+] from H2O 3 Changes in pH with Dilution qWhat is the pH for each dilution? q What is the pH of 1.0 M HCl? q pH = 0.00 q What is the pH of 0.10 M HCl (a 1:10 dilution)? q pH = 1.00 q What is the pH of 0.010 M HCl? q pH = 2.00 3 Changes in pH with Dilution q What is the pH of 1.0 x 10-3 M HCl? q pH = 3.00 q What is the pH of 1.0 x 10- 4 M HCl? q pH = 4.00 q What is the pH of 1.0 x 10-5 M HCl? q pH = 5.00 q What is the pH of 1.0 x 10-6 M HCl? q pH = 5.996 3 Changes in pH with Dilution q What is the pH of 1.0 x 10-7 M HCl? q pH = 6.791 q What is the pH of 1.0 x 10-8 M HCl? q pH = 6.996 q Why does the pH stop changing at a value of about 7? q Water has a pH of 7 due to autodissociation, so it is never possible to get a pH higher than 7 by addition of water. 3 Strong Acids and Bases Strong Bases q Be careful of stoichiometry!!! q What is the pOH of 0.1 M Ca(OH)2? The pH? q pOH = 0.7, not 1.0; pH = 13.3 4 Strong Acids and Bases Strong Bases q Which of the following solutions should have the highest pH? q 0.01 M NaOH q 0.01 M Ba(OH)2 4 How do we Measure pH? q Litmus or pH paper q Color changes of indicators q Voltage generated by electrodes (pH meter) 4 pH Indicators 4 Concentration from pH q pH = -log[H3O+] q Rearrange: q [H3O+] = 10-pH q Similarly: q [OH-] = 10-pOH 4 A 50-L solution has a pH of 9.5. What is [OH-], and how many moles of OHare there? 25% 25% 25% 25% 1. [OH-]=3.2 x 10-10 moles = 1.6 x 10-8 2. [OH-]=3.2 x 10-5 moles = 1.6 x 10-3 3. [OH-]=4.6 x 10-4 moles = 2.3 x 10-2 4. [OH-]=4.6 x 10-7 moles = 2.3 x 10-5 1 2 3 4 4 ...
View Full Document

Ask a homework question - tutors are online