14.1 Intro to Acids and Bases 14.2 Acid Strength 14.3 pH Scale Ch. 14: Acids and Bases 14.1 Intro to Acids and Bases 14.2 Acid Strength 14.3 pH Scale

Definitions Arrhenius Bronsted-Lowry ______: produce H+ in aqueous solution ______: produces OH- in aqueous solution very limited Bronsted-Lowry ______: H+ donor ______: H+ acceptor more general

Conjugate Acid-Base Pair HA(aq) + H2O(l) ⇄ H3O+(aq) + A-(aq) 2 substances that are connected by a donating and accepting of H2O really a “fight” over H+ between two bases: ______ and ______ if A- has a greater attraction, rxn lies to _____ if H2O has greater attraction, rxn lies to _____ This helps with #29 on HW

Acid dissociation constant (Ka) equilibrium expression where H+ is removed to form conjugate base HA + H2O ⇄ H3O+ + A- Don’t include H2O

Strength determined by equilibrium position of dissociation reaction strong acid: lies far to right, almost all HA is _____________. ________________ creates weak conjugate base weak acid: lies far to left, almost all HA is stays as _____. creates strong conjugate base This helps with #33 on HW

Water is a stronger base than the CB of a strong acid but a weaker base than the CB of a weak acid Water is a stronger acid than the CA or a strong base but a weaker acid than the CA if a weak base

Types of Acids __________: an acid with 2 acidic protons __________: ex. HNO3 most acids are this type where the acidic proton is attached to an oxygen _________________: ex. CH3COOH containing a carboxyl group usually weak _________________: ex. HBr hydrogen and a halogen

Autoionization 2 water molecules exchange H+ H2O + H2O ⇄ H3O+ +OH- Kw= dissociation constant for water at 25C, [H+]=[OH-]=1.0 x 10-7 so at 25C, Kw=1.0x10-14 How will change it with temperature?

pH scale pH= pOH= [H+]= [OH-]= pH ____________ as [H+] ______________ This helps with #37, 41, 43 on HW

Example 1 Write the ionization or dissociation reaction and the Ka expression for each of the following: acetic acid – (HCH3COO) ammonium ion – (NH4+)

Example 2 Determine the acid, base, conj. acid, and conj. base in each reaction: NH4+(aq) + CN-(aq) ⇄ HCN(aq) + NH3(aq (CH3)3N(aq) + H2O(l) ⇄ (CH3)3NH+(aq) + OH-(aq) HCHO2(aq) + PO43-(aq) ⇄ CHO2-(aq) + HPO42-(aq)

Example 3 Determine which species is a stronger base: F- or Cl- Determine which species is a stronger acid: H2O or NH4+

Example 4 The [OH-] of a solution at 25C is 1.0 x 10-5 M. Determine the [H+], pH and pOH.

Example 5 The pH of a solution at 25C is 5.77. Calculate the pOH, [OH-] and [H+].

14.4-5 pH of Acidic Solutions Ch. 14: Acids and Bases 14.4-5 pH of Acidic Solutions

Strong Acids SA completely form ions so you do not need to use Ka and I-C-E chart Finding the pH of 0.10 M HNO3 Always write the important species present at the beginning of each problem H+ , NO3-, H2O water will exist as H+ and OH- but only a small amount- so it can be ignored HNO3  H+ + NO3- [H+] = 0.10 M pH = -log(0.10) = 1.00

Strong Acids Find the pH of 1.0 x 10-10 M HCl

Weak Acids Write major species Decide on which can provide H+ ions Make ice chart Put equilibrium values in Ka expression Check validity of assumption (x must be less than 5% of initial conc) Find pH

Weak Acids- Example Calculate the pH of 1.00 M solution of HF (Ka = 7.2 x 10-4)

Weak Acids- Example HF  H+ + F- I C E

Weak Acids- Example Check assumption: pH =

Weak Acid- Example 2 HOCl  H+ + OCl- Find pH of 0.100 M solution of HOCl (Ka = 3.5x10-8) HOCl, H2O HOCl will provide much more H+ than H2O – ignore H2O HOCl  H+ + OCl- I C E

Weak Acid- Example 2 Check assumption: pH =

Mixtures of Weak Acids When dealing with a mixture of acids, consider the strongest acid first then, use the “Equilibrium” values from it to begin your weaker acid

Mixtures of Weak Acids Find the pH of a mixture of 1.00 M HCN (Ka=6.2x10-10) and 5.00 M HNO2 (Ka=4.0x10-4) HNO2 is most important b/c it has highest Ka value HNO2  H+ + NO2- I C E

Mixtures of Weak Acids HCN  H+ + CN- I C E

Mixtures of Weak Acids [H+]= pH = [CN-] = Find the [CN-] at equilibrium [CN-] =

Percent Dissociation also called Percent Ionization for a weak acid, the % dissociation increases as molarity decreases dilution shifts equilibrium to side with greater number of particles

Percent Dissociation

Calculate Percent Dissociation for 1.0 M acetic acid (Ka=1.8x10-5) CH3COOH  H+ + CH3COO- I C E

Calculate Percent Dissociation

Calculate Percent Dissociation For 0.100 M CH3COOH

Percent Dissociation In a 0.200 M solution of a weak acid, 2.5% of the acid is dissociated. Find the Ka.

HA  H+ + A- I C E

Ch. 14: Acids and Bases 14.6 Bases

Bases

Bases Strong Bases Find pH of 5.0x10-2 M NaOH solution What would be another way to get pH? What if it was a Ca(OH)2 solution?

Bases Weak Bases do not contain OH- accepts H+ from H2O to make OH- usually have at least one unshared pair of electrons used to form bond with hydrogen

B(aq) + OH-(l)  BH+(aq) + OH-(aq) Bases Kb refers to reaction of base with water to make conjugate acid and OH- for weak bases only B(aq) + OH-(l)  BH+(aq) + OH-(aq)

Example Find the pH for 15.0 M solution of NH3 (Kb = 1.8x10-5) NH3 will create more OH- than water so autoionization can be ignored NH3 + H2O  NH4+ + OH- I C E

Example

Example Codeine (C18H21NO3) is a weak organic base. A 5.0x10-3 M solution of codeine has a pH of 9.95. Calculate the Kb for this substance. What is the chemical reaction?

Example C18H21NO3 + H2O ⇄ HC18H21NO3+ + OH- I C E x = [OH-] = 8.9x10-5

Ch. 14: Acids and Bases 14.7 Polyprotic Acids

Polyprotic Acids acids that can donate more than one H+ always dissociate one at a time Example: carbonic acid Ka1= 4.3x10-7 Ka2 = 5.6x10-11 Ka1 > Ka2 > Ka3 for typical weak polyprotic acid

Important Polyprotic Acids phosphoric acid: H3PO4 only 1st step creates important amount of H+ sulfuric acid: H2SO4 1st step is strong (H2SO4 is a strong acid) 2nd step is weak (HSO4- is a weak acid)

Example Find the pH of a 1.00x10-2 M sulfuric acid solution H+, HSO4-, H2O From 1st dissociation, [H+]= 1.00x10-2 M HSO4-  SO42- + H+ I C E

Example

14.8 Acidic and Basic Properties of Salts Ch. 14 Acids and Bases 14.8 Acidic and Basic Properties of Salts

Salts another word for ionic compounds when soluble salts are dissolved, they break up into ions that can be either acidic or basic the acidic or basic ions make the solution acidic or basic

Determining A/B of a Salt Figure out what each ion in the salt comes from Ex: KCN K+ comes from strong base, _______ CN- comes from weak acid, _______ Determine what quality that gives each ion K+ must be weak _________ CN- must be strong _________ Compare and determine the overall acidity or basicity of solution overall: ____________________

Cations Weak Conj. Acid Strong Conj. Acid from Strong B K+, Ca2+ from KOH and Ca(OH)2 Strong Conj. Acid from weak B NH4+, C5H5NH+ from NH3 and C5H5N and highly charged metal ions (Al3+ or Fe3+)

Anions weak Conj. Base strong Conj. Base from Strong Acid Cl-, HSO4- from HCl and H2SO4 strong Conj. Base from Weak Acid HCO32-, NO2- from H2CO3 and HNO2

Acidic and Basic? If it is difficult to tell the overall quality, compare the K values to determine the type of solution Ka > Kb : _________ Kb > Ka : _________ Ka*Kb = Kw for any weak acid and its CB

Practice Predict which of the following will be acidic, basic or neutral NH4Br NH4+ Br- overall: FeCl3 Fe+3 Cl-

Practice Na2CO3 Na+ CO32- overall: KClO4 K+ ClO4 NaHC2O4 HC2O4-

Example Find the pH of a 0.20 M solution of KF. KF  K+ + F- which of these will effect the pH of the solution? F- + H2O  HF + OH- I C E

Example

Summary

Ch. 14 Acids and Bases 14.9 Structure

Why are some H’s acidic? acidic: non-acidic weak bonds strong bonds polar bonds non-acidic strong bonds nonpolar bonds

Factors in Acidity Overall: the ______________ the bond to the H is, the ___________ the acid is If the atoms around the bond are more electronegative, they will pull electron density away from the bond that will make the bond weaker Electronegativity of halogen the more electronegative the halogen is, the more polar the bond is, and the stronger the acid is

Factors in Acidity Size of atoms the ___________ the atoms, the weaker the bond, the ___________the acid Ex: H-F, H-Cl, H-Br, H-I H-F has the most polar bond but it is a weak acid- Why? H and F are both tiny atoms so have a stronger attraction to each other H-I has very weak bond b/c I is large so is a strong acid

Factors in Acidity Number of Oxygens in Oxyacid the _________ the number of oxygens, the more polar the bond is, the _________ the acid is

Example Which is the stronger acid? Explain HNO2 or HClO2 HNO3 or HNO2 CCl3COOH or CH3COOH

Ch. 14 Acids and Bases 14.10 Oxides

H-O-X If X is relatively electronegative If X is not electronegative H-O bond is weaker and breaks easily HOX  If X is not electronegative O-X bond will break

Acidic Oxides when a covalent oxide dissolves in water, an acidic solution forms Ex: SO2, CO2, NO2 how do you determine what acid is formed? be sure the nonmetal atom keeps the same oxidation state SO2 + H2O 

Basic Oxides when an ionic oxide dissolves in water, a basic solution forms Na2O, CaO, K2O Na2O + H2O 

Ch. 14 Acids and Bases 14.11 Lewis Acid-Base Model

Lewis Model even more general than Bronsted-Lowry acid base electron pair ____________ has empty atomic orbitals base has lone pair

Examples Al3+ + 6H2O  [Al(H2O)6]3+ SO3 + H2O  H2SO4