2 CHAPTER OUTLINE General Properties Arrhenius Acids & Bases Strength of Acids & BasesBrønsted-Lowery Acids & BasesIonization of WaterpH and pOH Scales
3 GENRAL PROPERTIES OF ACIDS & BASES Many common substances in our daily lives are acids and bases.Oranges, lemons and vinegar are examples of acids. In addition, our stomachs contain acids that help digest foods.Antacid tablets taken for heartburn and ammonia cleaning solutions are examples of bases.
4 GENRAL PROPERTIES OF ACIDS General properties associated with acids include the following:sour tastechange color of litmus from blue to redreact with metals to produce H2 gasreact with bases to produce salt & water
5 Structure of Acidsbinary acids have acid hydrogens attached to a nonmetal atomHCl, HFHydrofluoric acid
6 Structure of Acidsoxy acids have acid hydrogens attached to an oxygen atomH2SO4, HNO3
7 Structure of Acids carboxylic acids have COOH group HC2H3O2, H3C6H5O3only the first H in the formula is acidicthe H is on the COOH
8 GENRAL PROPERTIES OF BASES General properties associated with bases include the following:bitter tasteslippery, soapy feelingchange color of litmus from red to bluereact with acids to produce salt & water
9 Structure of Bases most ionic bases contain OH ions NaOH, Ca(OH)2some contain CO32- ionsCaCO3 NaHCO3molecular bases contain structures that react with H+mostly amine groups
10 amine groupsAmmoniaH – N – HH+ H+HH – N+ – HHAmmonium ion
11 ARRHENIUS ACIDS & BASES According to the Arrhenius definition,Acids are substances that produce hydronium ions (H3O+) in aqueous solution.The most common definition of acids and bases was formulated by the Swedish chemist Svante Arrhenius in 1884.HCl (g) + H2O (l) H3O+ (aq) + Cl– (aq)Commonly written asHCl (g) H+ (aq) + Cl– (aq)H2O
12 ARRHENIUS ACIDS & BASES According to the Arrhenius definition,Bases are substances that produce hydroxide ion (OH-) in aqueous solution.NaOH (s) Na+ (aq) + OH– (aq)H2ONH3 (aq) + H2O (l) NH4+ (aq) + OH – (aq)
13 BRØNSTED-LOWRY ACIDS & BASES According to Brønsted-Lowry definition, an acid is a proton donor, and a base is a proton acceptor.The Arrhenius definition of acids and bases is limited to aqueous solutions.A broader definition of acids and bases was developed by Brønsted and Lowry in the early 20th century.A substance that can act as a Brønsted-Lowry acid and base (such as water) is called amphiprotic.BaseAcidAcidBaseNH3 (aq) + H2O (l) → NH4+ (aq) + OH– (aq)HCl (g) + H2O (l) → H3O+ (aq) + Cl– (aq)
14 BRØNSTED-LOWRY ACIDS & BASES In Brønsted-Lowry definition, any pair of molecules or ions that can be inter-converted by transfer of a proton is called conjugate acid-base pair.HCl (g) + H2O (l) → H3O+ (aq) + Cl– (aq)Conjugate acidConjugate baseAcidBase
16 Example 1:Identify the conjugate acid-base pairs for each reaction shown below:H2O Cl HCl OHConjugate acidAcidBaseConjugate base
17 Example 1:Identify the conjugate acid-base pairs for each reaction shown below:C6H5OH + C2H5O C6H5O + C2H5OHConjugate baseConjugate acidAcidBase
18 Example 2: HS + H+ H2S NH3 + H+ NH4+ CO32 + H+ HCO3 Write the formula for the conjugate acid for each base shown:HS+ H+ H2SNH3+ H+ NH4+CO32+ H+ HCO3
19 Example 3: HI - H+ I CH3OH - H+ CH3O HNO3 - H+ NO3 Write the formula for the conjugate base for each acid shown:HI- H+ ICH3OH- H+ CH3OHNO3- H+ NO3
20 ACID & BASE STRENGTHAccording to the Arrhenius definition, the strength of acids and bases is based on the amount of their ionization in water.Strong acids and bases are those that ionize completely in water.Strong acids and bases are strong electrolytes.1001001001M1M1M
21 ACID & BASE STRENGTHWeak acids and bases are those that ionize partially in water.Weak acids and bases are weak electrolytes.100~1~11M~0.01M~0.01M
22 IONIZATION OF STRONG vs. WEAK ACIDS Ionizes completelyIonizes partially
26 Titrationusing reaction stoichiometry to determine the concentration of an unknown solutionTitrant (unknown solution) added from a buretindicators are chemicals added to help determine when a reaction is completethe endpoint of the titration occurs when the reaction is complete
28 Titration The base solution is the titrant in the buret. As the base is added tothe acid, the H+ reacts withthe OH– to form water.But there is still excessacid present so the colordoes not change.At the titration’s endpoint,just enough base has beenadded to neutralize all theacid. At this point theindicator changes color.
29 Find: concentration HCl, M Example 1The titration of mL HCl solution of unknown concentration requires mL of M NaOH solution to reach the end point. What is the concentration of the unknown HCl solution?Find: concentration HCl, MCollect Needed Equations and Conversion Factors:HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) 1 mole HCl = 1 mole NaOH0.100 M NaOH 0.100 mol NaOH 1 L sol’n
31 IONIZATION OF WATER H2O + H2O H3O+ + OH– Water can act both as an acid and a base.In pure water, one water molecule donates a proton to another water molecule to produce ions.H2O H2O H3O OH–Conjugate acidAcidBaseConjugate base
32 IONIZATION OF WATER [H3O+] = [OH–] = 1.0 x 10-7 M Kw=[H3O+][OH–] All aqueous solutions have H3O+ and OH– ions.An increase in the concentration of one of the ions will cause an equilibrium shift that causes a decrease in the other one.When the concentrations of H3O+ and OH– are multiplied together, the ion-product constant (Kw) is formed.In pure water, the transfer of protons between water molecules produces equal numbers of H3O+ and OH– ions.The number of ions produced in pure water is very small, as indicated below:[H3O+] = [OH–] = 1.0 x 10-7 MKw=[H3O+][OH–]=[1.0x10-7][1.0x10-7]=1.0x10-14
33 ACIDIC & BASIC SOLUTIONS When [H3O+] is greater than [OH–] in a solution, it is acidic.For example, if [H3O+] is 1.0 x 10–4 M, then [OH–] would be 1.0 x 10–10 M.When [H3O+] and [OH–] are equal in a solution, it is neutral.
34 ACIDIC & BASIC SOLUTIONS When [OH-] is greater than [H3O+] in a solution, it is basic.For example, if [OH-] is 1.0 x 10–6 M, then [H3O+] would be 1.0 x 10–8 M.
38 Example 1: pH = -log [H3O+] = -log [1.4x10-9] = -(-8.85) pH = 8.85 The [H3O+] of a liquid detergent is 1.4x10–9 M. Calculate its pH.Solution is basicpH = -log [H3O+]= -log [1.4x10-9]= -(-8.85)2 significant figurespH = 8.85The number of decimal places in a logarithm is equal to the number of significant figures in the measurement.
39 Example 2: The pH of black coffee is 5.3. Calculate its [H3O+]. Solution is acidic[H3O+] = antilog (-pH)= 10 –pH =1 significant figure[H3O+] = 5 x 10-6
40 Example 3: pH = -log [H3O+] = -log [3.5x10-3] = -(-2.46) pH = 2.46 The [H3O+] of a solution is 3.5 x 10–3 M. Calculate its pH.Solution is acidicpH = -log [H3O+]= -log [3.5x10-3]= -(-2.46)2 significant figurespH = 2.46
41 Example 4: The pH of tomato juice is 4.1. Calculate its [H3O+]. Solution is acidic[H3O+] = antilog (-pH)= 10 –pH =1 significant figure[H3O+] = 8 x 10-5
42 Example 5: Kw=[H3O+][OH–] The [OH] of a cleaning solution is 1.0 x 105 M. What is the pH of this solution?Solution is basicKw=[H3O+][OH–]2 sig figs[H3O+] == 1.0 x 109 MpH =log[H3O+]= log(1.0x109)= 9.00
43 Example 6:The pH of a solution is Calculate the [H3O+] for this solution.Solution is basic[H3O+] = antilog (-pH)= 10 –pH =[H3O+] = 3.2 x 10-12