Chapter 8

Acids and Bases

Chemistry B11

Acids and Bases

Acids: sour

Bases: bitter or salty

Acids and Bases

NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)

Acid: produces H3O+

Base: produces OH-

Arrhenius definition:

CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+(aq)

H3O+ (Hydronium ion): H+(aq) + H2O(l) H3O+(aq)

NaOH(s) Na+(aq) + OH-(aq)H2O

Acids and Bases

Acid: donates H+ (proton)

Bronsted and Lowry definition: (If H2O is not involved.)

Base: accepts H+ (proton)

CH3COOH + NH3 CH3COO- + NH4+

acid base Conjugate base

Conjugate acid

Conjugate acid-base pair

Conjugate acid-base pair

Acids and Bases

HCl + H2O Cl- + H3O+

acid base Conjugate base

Conjugate acid

C6H5OH + H2OC6H5O- + H3O+

acid base Conjugate base

Conjugate acid

Conjugate acid-base pair

Conjugate acid-base pair

Conjugate acid-base pair

Conjugate acid-base pair

Acids and Bases

Weak acid or base: is partially ionized in aqueous solution.

CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+(aq)

Strong acid or base: is completely ionized in aqueous solution.

HCl(aq) + H2O(l) Cl-(aq) + H3O+(aq)

NaOH(aq) + H2O(l) Na+(aq) + OH-(aq)

NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)

produces less H+ and OH-

produces more H+ and OH-

Acids and Bases

C2H5OH C2H5O-

H2O OH-HPO4

2- PO43-

HCO3- CO3

2-

C6H5OH C6H5O-

HCN CN-NH3NH4

+H2PO4

- HPO42-

H2S HS-H2CO3 HCO3

-CH3COOH CH3COO

-H3PO4 H2PO4

-HSO4

- SO42-

H2OH3O+

HNO3 NO3-

H2SO4 HSO4-

HCl Cl-HI I-Hydroiodic acid

Hydrochloric acidSulfuric acid

Dihydrogen phosphateAcetateBicarbonate

Hydrogen phosphateAmmonia

Phenoxide

Carbonate

PhosphateHydroxideEthoxide

Hydrogen sulfide

Nitric acidHydronium ion

Hydrogen sulfate ion

Name of acid Name of ion

Phosphoric acidAcetic acidCarbonic acid

Dihydrogen phosphateAmmonium ion

Phenol

Bicarbonate ion

Hydrogen phosphate ionWaterEthanol

Hydrogen sulfide

AcidConjugate Base

IodideChlorideHydrogen sulfateNitrateWater

Sulfate

StrongAcids

Weak Acids

Weak Bases

StrongBases

Hydrocyanic acid Cyanide

A strong acid contains a weak conjugate base.

Acids and Bases

Monoprotic acids

HCl

Diprotic acids

H2SO4

Triprotic acids

H3PO4

Amphiprotic: it can act as either acid or a base.

HCl(aq) + H2O(l) Cl-(aq) + H3O+(aq)

NaOH(aq) + H2O(l) Na+(aq) + OH-(aq)

base

acid

Naming binary acids

Hydro -ide ion -ic acidAnion :+

HF F-: flouride ion Hydroflouric acid

HCl Cl-: chloride ion Hydrochloric acid

H2S S2-: sulfuride ion Hydrosulfuric acid

Naming ternary acids

Anion: -ite ion -ous acid

-ate ion -ic acid

HNO3 NO3-: Nitrate ion Nitric acid

HNO2 NO2-: Nitrite ion Nitrous acid

H2CO3 CO32-: carbonate ion carbonic acid

H2SO3 SO32-: sulfurite ion sulfurous acid

HA + H2O A- + H3O+

Ionization constant

K =[A-] [H3O+]

[HA] [H2O]

- Log Ka = pKa

not for strong acids

Ka ↑ or pKa ↓ Stronger acid

Ka = K [H2O] =[A-] [H3O+]

[HA]Acid ionization constant Ka < 1

Equilibrium constant

pH and pOH

pH + pOH = 14

H2O + H2O OH- + H3O+

KW = [H3O+] [OH-] = (1×10-7) (1×10-7)

[H3O+] [OH-] = 1×10-14

pH and pOH

pH = - log [H3O+] or -log [H+]

pOH = - log [OH-]

0

Acid Neutral Base

7 14

pH scale:

[H3O+] ↑ [H3O+] ↓ and [OH-] ↑

pH meter and pH indicators

Nature & pH indicators

Bigleaf Hydrangea

In acidic soilIn basic soil (alkaline)

Acid Reactions

1. Reaction with metals (strong acids): a salt and H2 are produced.

Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)

2. Reaction with metal hydroxides: a salt and water are produced.

KOH(aq) + 2HCl(aq) KCl(aq) + H2O(l)

Acid Reactions

3. Neutralization: reaction between an acid and a base.

A salt and water are produced.

KOH(aq) + 2HCl(aq) KCl(aq) + H2O(l)

2NaOH(aq) + H2SO4(aq) Na2SO4(aq) + 2H2O(l)

Strong acid reacts with strong base

to produce the weaker acid and weaker base.

(This is the direction of a reaction)

Titration (Neutralization reaction)

MB: known

VB: knownB

A

MA: unknown

VA: known

Equivalence point:

Equal amount of acid (H+) and base (OH-) (pH = 7).

2NaOH + 1H2SO4 2NaSO4 + 2H2O

MA × VA MB × VB=

Coefficient A Coefficient B

Buffers

Acid or Base

Buffer

pH stays constant.

A buffer resists changes in pH when limited amounts of acid or base are added.

Buffers

Our blood is a buffer solution.

pH of blood ≈ 7.4

Shock Absorber

Acid

Acid

Base

Buffer Composition

Weak Acid + its Conjugate base (in equilibrium)

salt of the weak acid

CH3COOH + CH3COO-Na+

CH3COOH / CH3COO-

Carbonate buffer H2CO3 / HCO3-

Phosphate buffer H2PO4- / HPO4

2-

Proteins buffer

Buffers

How do buffers work?

Carbonate buffer H2CO3 / HCO3-

If we eat an acidic food: HCO3- + H3O+ → H2CO3 + H2O

H2CO3 + OH- → HCO3- + H2OIf we eat a basic food:

Henderson-Hasselbalch equation

pH = pKa + log [A-][HA]

pH of Buffers

[HA]: concentration of the weak acid

[A-]: concentration of its conjugate base

pKa of the weak acid

HA(aq) A-(aq) + H+(aq)

Weak acid Conjugate base