Chapter 16 Acids and Bases
Copyright © by McDougal Littell. All rights reserved. Acids and Bases Characteristics of acids: sour, corrosive, conducts electricity Characteristics of bases: bitter, slippery, corrosive, conducts electricity Copyright © by McDougal Littell. All rights reserved.
pure water, sugar solution Electrolytes Strong - conduct current efficiently NaCl, HNO3 Weak - conduct only a small current vinegar, tap water Non - no current flows pure water, sugar solution
Copyright © by McDougal Littell. All rights reserved. Acids Strong acids -dissociate completely to produce H+ in solution hydrochloric and sulfuric acid Weak acids - dissociate to a slight extent to give H+ in solution acetic and hydrofluoric Copyright © by McDougal Littell. All rights reserved.
HCl(aq) is completely ionized.
Acetic acid (HC2H3O2) exists in water mostly as undissociated molecules. Only a small percentage of the molecules are ionized.
Models of Acids and Bases Arrhenius Concept: Acids produce H+ in water Bases produce OH in water HCl Cl + H+ NaOH Na+ + OH- NH3 + H2O NH4+ + OH- Copyright © by McDougal Littell. All rights reserved.
Copyright © by McDougal Littell. All rights reserved. Brønsted-Lowry: Acids are H+ donors Bases are H+ acceptors examples: HCl + H2O Cl + H3O+ acid base NaOH + HCl NaCl + H2O NH3 + HCl NH4+ + Cl- Copyright © by McDougal Littell. All rights reserved.
Conjugate Acid/Base Pairs HA(aq) + H2O(l) H3O+(aq) + A(aq) conj conj conj conj acid 1 base 2 acid 2 base 1 conjugate base: like the conjugate acid, but with one less H conjugate acid: like the conjugate base, but with one more H Copyright © by McDougal Littell. All rights reserved.
Copyright © by McDougal Littell. All rights reserved. Question Identify the conjugate acid base pairs: HF + OH- F- + H2O NH3 + H2SO4 NH4+ + HSO4- HClO4 + H2O H3O+ + ClO4- Copyright © by McDougal Littell. All rights reserved.
Conjugate Acid/Base Strength Copyright © by McDougal Littell. All rights reserved.
Water as an Acid and a Base Water is amphoteric (it can behave either as an acid or a base). H2O H+ + OH Kw = 1 1014 = [H+][OH-] If [H+] > [OH-] acidic If [H+] < [OH-] basic If [H+] = [OH-] neutral Copyright © by McDougal Littell. All rights reserved.
Reaction of Acid with Water HCl + H2O H3O+ + Cl- H3O+ is called the hydronium ion H3O+ is equivalent to H+ So we usually just write it like: HCl H+ + Cl- Copyright © by McDougal Littell. All rights reserved.
Copyright © by McDougal Littell. All rights reserved. Question: Calculate the [H+] if [OH-] = 1.0 x 10-5 M Is the solution acidic or basic? Copyright © by McDougal Littell. All rights reserved.
Copyright © by McDougal Littell. All rights reserved. Question: Calculate the [OH-] if the [H+] = 2.6 x 10-8 M Is the solution acidic or basic? Copyright © by McDougal Littell. All rights reserved.
Copyright © by McDougal Littell. All rights reserved. Question: Calculate the [H+] and [OH-] for a 0.15 M HCl solution. Copyright © by McDougal Littell. All rights reserved.
Copyright © by McDougal Littell. All rights reserved. Question: Calculate the [H+] and [OH-] for a 0.025 M H2SO4 solution. Copyright © by McDougal Littell. All rights reserved.
Copyright © by McDougal Littell. All rights reserved. The pH Scale pH = log[H+] pH in water ranges from 0 to 14. Kw = 1.00 1014 = [H+] [OH] pKw = 14.00 = pH + pOH pOH = -log[OH-] As pH rises, pOH falls (sum = 14.00). Copyright © by McDougal Littell. All rights reserved.
Copyright © by McDougal Littell. All rights reserved. Question Calculate the pH for the following: [H+] = 1 x 10-9 M [H+] = 3.2 x 10-3 M [OH-] = 4 x 10-8 M Copyright © by McDougal Littell. All rights reserved.
Copyright © by McDougal Littell. All rights reserved. The pH scale. Acidic: pH < 7 Basic: pH > 7 Neutral: pH = 7 Copyright © by McDougal Littell. All rights reserved.
Copyright © by McDougal Littell. All rights reserved. Question Calculate the pH for the following: 0.004 M HCl 1.5 M NaOH 0.015 M H2SO4 Copyright © by McDougal Littell. All rights reserved.
Copyright © by McDougal Littell. All rights reserved. Question Calculate the [H+] for the following: pH = 4.5 pH = 11.5 pOH = 5.6 Copyright © by McDougal Littell. All rights reserved.
Copyright © by McDougal Littell. All rights reserved. Indicators – turn a certain color at a particular pH Litmus paper: Is red in acidic solution Is blue in basic solution pH paper: has a combination of indicators to give a more precise measurement of pH pH meter: uses voltage to measure the pH very accurately Copyright © by McDougal Littell. All rights reserved.
Figure 16.4: Useful pH ranges for several common indicators. Copyright © by McDougal Littell. All rights reserved.
Copyright © by McDougal Littell. All rights reserved. Titration Copyright © by McDougal Littell. All rights reserved.
Copyright © by McDougal Littell. All rights reserved. Titration Standard solution: the solution of accurately known concentration The buret holds the standard solution; the solution of unknown concentration is in the beaker An indicator is in the beaker solution which will change color when the correct amount of standard solution is added (equivalence point) Copyright © by McDougal Littell. All rights reserved.
Copyright © by McDougal Littell. All rights reserved. Titration Equivalence point: equivalent amounts of acid and base have reacted For a strong acid + strong base, the equivalence point occurs at pH = 7 The pH of the solution changes dramatically near the equivalence point Copyright © by McDougal Littell. All rights reserved.
Copyright © by McDougal Littell. All rights reserved. The pH curve for the titration of 50.0 mL of ? M HNO3 with 0.100 M NaOH. Copyright © by McDougal Littell. All rights reserved.
Copyright © by McDougal Littell. All rights reserved. Question For the titration in the previous slide, calculate the concentration of the HNO3. Copyright © by McDougal Littell. All rights reserved.
Copyright © by McDougal Littell. All rights reserved. Question A 100 mL sample of 0.15 M HCl is titrated with 0.60 M KOH. What volume of KOH would be required to reach the endpoint? Copyright © by McDougal Littell. All rights reserved.