Acids and BasesPart 2

Classifying Acids and Bases

ArrheniusAcid

◦ Increases hydrogen ions (H+) in water

◦ Creates H3O+ (hydronium)

Base◦ Increases OH- in

water

Classifying Acids and Bases

Brønsted - Lowry

Acid◦ Proton donor (H+)◦ Must have

hydrogen in formula

Base◦ Proton acceptor

(H+)Water can be an

acid or a base

Classifying Acids and Bases

LewisAcid

◦ Electron pair acceptor

◦ Usually positive ions

Base◦ Electron pair

donor◦ Usually negative

ions

PairsAcid + Base Conjugate acid

+ Conjugate base

This is an equilibrium.The acid becomes the conjugate

base after it has donated the H+

The base becomes the conjugate acid once it accepts the H+

Conjugate Acids and BasesIdentify the acid, base, conjugate

acid, and conjugate base in the below reaction:

HF + H2O → F- + H3O+

Acid Base conjugate conjugate

base acid

WaterWater conducts electricity

◦ElectrolyteThus, water self-ionizesH2O → H+ + OH- Water is also Amphoteric

◦Can act as either an acid or a baseTherefore:2H2O → H3O+ + OH-

Types of AcidsMonoprotic

◦Only 1 acidic hydrogen Polyprotic Acids

◦More than 1 acidic hydrogen◦Diprotic – H2SO4

◦Triprotic – H3PO4

Oxyacids ◦Proton is attached to the oxygen of an ion.

Organic acids◦Contain the Carboxyl group –COOH◦H attached to O – ex: CH3COOH – acetic acid

◦Generally very weak

Strong Acids They completely dissociate in

water◦HCl◦HNO3

◦HI◦H2SO4

◦HClO◦HBr

pH of Strong AcidCalculate the pH and [OH]:

◦For a 1 x 10-3 M solution of HClO4

Bases

The OH- is a strong base.

Hydroxides of the alkali metals are strong bases because they dissociate completely when dissolved.

Others are weak.

Bases without OH-

Bases are proton acceptors.

NH3 + H2O NH4+ + OH-

It is the lone pair on nitrogen that accepts the proton.

Salts as acids and basesSalts are ionic compounds.Salts of the cation of strong

bases and the anion of strong acids are neutral.

Salts of a strong acid and weak base are acidic salts

Salts of strong base and weak acids are basic salts

Lewis Acids and BasesMost general definition.Acids are electron pair acceptors.Bases are electron pair donors.

B FF

F

:NH

H

H

Ion concentrationsThe concentrations of H3O+ and OH- are

based on waterKw – ion-product constant of waterAt 25°C, Kw = 1.0x10-14

Kw = (Ka)(Kb) [H3O+][OH-][H3O+] – concentration of hydronium ion[OH-] – concentration of hydroxide ionNeutral: [H3O

+] = [OH-]= 1.0 x10-7

Acidic:[H3O+] > [OH-]

Basic: [H3O+] < [OH-]

Acid dissociation constant

Acid dissociation constant Ka

Base dissociation constant Kb

The larger the number the stronger the substance

The smaller the number the weaker the substance

Calculating pHpH is a measure of hydronium

[H3O+] concentration in solutionLower pH = more acidicpH = -log [H3O+]

pH Scale

pH CalculationsWhat is the pH of a neutral

solution ([H3O+] = 1.0x10-7M)?◦pH = 7

What is the pH of a solution if:[H3O+] = 1.0x10-4M?

◦pH = 4[H3O+] = 0.0015M?

◦pH = 2.8

Calculating pOHpOH is a measure of hydroxide

[OH-] concentration in solutionHigher pOH = more acidicpOH = - log [OH-]pH + pOH = 14

pOH CalculationsWhat is the pOH of a neutral

solution ([OH-] = 1.0x10-7M)?What is the pOH of a solution if:[OH-] = 8.22x10-6M?

◦pOH = 5.09[OH-] = 0.0541M?

◦pOH = 1.27

BasicAcidic Neutral

100

10-

1

10-

3

10-

5

10-

7

10-910-1110-

13

10-14

[H+]

0 1 3 5 7 9 11

13

14

pH

Basic 10010-

1

10-

3

10-

5

10-

7

10-910-

11

10-

13

10-14

[OH-]

013579111314

pOH