Part II

Polyprotic acid

HH22COCO33 HH++ + HCO + HCO33--

KaKa11= 4.3 x 10= 4.3 x 10-7-7

HCOHCO33-- HH++ + CO + CO33

-2-2

KaKa22= 4.3 x 10= 4.3 x 10-10-10

Base in first step is acid in second.Base in first step is acid in second. In calculations we can normally ignore the In calculations we can normally ignore the

second dissociation.second dissociation.

Sulfuric acid is special

In first step it is a strong acid.In first step it is a strong acid.

KaKa22 = 1.2 x 10 = 1.2 x 10-2-2

Calculate the concentrations in a 2.0 M solution of Calculate the concentrations in a 2.0 M solution of HH22SOSO44

Calculate the concentrations in a 2.0 x 10Calculate the concentrations in a 2.0 x 10-3-3 M M solution of Hsolution of H22SOSO44

Salts as acids an bases

Salts are ionic compounds.Salts are ionic compounds. Salts of the cation of strong bases and the Salts of the cation of strong bases and the

anion of strong acids are neutral.anion of strong acids are neutral. for example NaCl, KNOfor example NaCl, KNO33

There is no equilibrium for strong acids and There is no equilibrium for strong acids and bases.bases.

We ignore the reverse reaction.We ignore the reverse reaction.

Basic Salts

If the anion of a salt is the conjugate base of a weak acid - If the anion of a salt is the conjugate base of a weak acid - basic solution.basic solution.

In an aqueous solution of NaFIn an aqueous solution of NaF The major species are NaThe major species are Na++, F, F--, and H, and H22OO

FF- - + H+ H22O O HF + OHHF + OH--

KKbb =[HF][OH=[HF][OH--]]

[F [F- - ]]

but Ka = [Hbut Ka = [H++][F][F--]] [HF][HF]

Basic Salts

KKaa x K x Kb b = [HF][OH= [HF][OH--]] x [Hx [H++][F][F--]]

[F[F- - ] ] [HF][HF]

Basic Salts

KKaa x K x Kb b = [HF][OH= [HF][OH--]] x [Hx [H++][F][F--]]

[F[F- - ] ] [HF][HF]

Basic Salts

KKaa x K x Kb b = [HF][OH= [HF][OH--]] x [Hx [H++][F][F--]]

[F[F- - ] ] [HF][HF]

Basic Salts

KKaa x K x Kb b = [HF][OH= [HF][OH--]] x [Hx [H++][F][F--]]

[F[F- - ] ] [HF][HF]

KKaa x K x Kb b =[OH=[OH--] [H] [H++]]

Basic Salts

KKaa x K x Kb b = [HF][OH= [HF][OH--]] x [Hx [H++][F][F--]]

[F[F- - ] ] [HF][HF]

KKaa x K x Kb b =[OH=[OH--] [H] [H++]]

KKaa x K x Kb b = K= KWW

Ka tells us Kb

The anion of a weak acid is a weak base.The anion of a weak acid is a weak base. Calculate the pH of a solution of 1.00 M Calculate the pH of a solution of 1.00 M

NaCN. KNaCN. Kaa of HCN is 6.2 x 10 of HCN is 6.2 x 10-10-10

The CNThe CN-- ion competes with OH ion competes with OH-- for the H for the H+ +

Acidic salts

A salt with the cation of a weak base and the anion A salt with the cation of a weak base and the anion of a strong acid will be basic.of a strong acid will be basic.

The same development as bases leads to The same development as bases leads to

KKaa x K x Kb b = K= KWW

Calculate the pH of a solution of 0.40 M NHCalculate the pH of a solution of 0.40 M NH44Cl Cl

(the K(the Kbb of NH of NH33 1.8 x 10 1.8 x 10-5-5).).

Other acidic salts are those of highly charged Other acidic salts are those of highly charged metal ions.metal ions.

Anion of weak acid, cation of weak base

KKaa > K > Kb b acidicacidic

KKaa < K < Kb b basicbasic

KKaa = K = Kb b NeutralNeutral

Structure and Acid base Properties

Any molecule with an H in it is a potential acid.Any molecule with an H in it is a potential acid. The stronger the X-H bond the less acidic The stronger the X-H bond the less acidic

(compare bond dissociation energies).(compare bond dissociation energies). The more polar the X-H bond the stronger the The more polar the X-H bond the stronger the

acid (use electronegativities).acid (use electronegativities). The more polar H-O-X bond -stronger acid.The more polar H-O-X bond -stronger acid.

Strength of oxyacids

The more oxygen hooked to the central The more oxygen hooked to the central atom, the more acidic the hydrogen.atom, the more acidic the hydrogen.

HClOHClO44 > HClO > HClO33 > HClO > HClO22 > HClO > HClO

Remember that the H is attached to an Remember that the H is attached to an oxygen atom.oxygen atom.

The oxygens are electronegativeThe oxygens are electronegative

Strength of oxyacidsStrength of oxyacids

Electron Density

Cl O H

Strength of oxyacidsStrength of oxyacids

Electron Density

Cl O HO

Strength of oxyacidsStrength of oxyacids

Cl O H

O

O

Electron Density

Strength of oxyacids

Cl O H

O

O

O

Electron Density

Hydrated metals

Highly charged Highly charged metal ions pull the metal ions pull the electrons of electrons of surrounding water surrounding water molecules toward molecules toward them.them.

Make it easier for Make it easier for HH++ to come off. to come off.

Al+3 OH

H

Acid-Base Properties of Oxides

Non-metal oxides dissolved in water can Non-metal oxides dissolved in water can make acids.make acids.

SOSO33 (g) + H (g) + H22O(l) O(l) H H22SOSO44(aq)(aq)

Ionic oxides dissolve in water to produce Ionic oxides dissolve in water to produce bases.bases.

CaO(s) + HCaO(s) + H22O(l) O(l) Ca(OH) Ca(OH)22(aq)(aq)

Lewis Acids and Bases

Most general definition.Most general definition. Acids are electron pair acceptors.Acids are electron pair acceptors. Bases are electron pair donors.Bases are electron pair donors.

B FF

F

:NH

H

H

Lewis Acids and Bases

Boron triflouride wants more electrons.Boron triflouride wants more electrons.

B FF

F

:NH

H

H

Lewis Acids and Bases

Boron triflouride wants more electrons.Boron triflouride wants more electrons. BFBF33 is Lewis base NH is Lewis base NH33 is a Lewis Acid. is a Lewis Acid.

BF

F

F

N

H

H

H

Lewis Acids and Bases

Al+3 ( )H

HO

Al ( )6

H

HO

+ 6

+3