Chapter 16

Acids and Bases

Chemistry B2A

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

(If H2O is involved.)

Acids and Bases

Acid: donates H+ (proton)

Base: accepts H+ (proton)

HCl + H2O Cl- + H3O+

acid base Conjugate base

Conjugate acid

Conjugate acid-base pair

Conjugate acid-base pair

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

H O

:

+ H Cl

:: : H O H

:

+H

+Cl -

::: ::

H

HCl + H2O Cl- + H3O+

Acids and Bases

Proton (H+) is transferred.

Acids and Bases

C6H5OH + H2OC6H5O- + H3O+

acid base Conjugate base

Conjugate acid

Conjugate acid-base pair

Conjugate acid-base pair

CH3COOH + NH3 CH3COO- + NH4+

acid base Conjugate base

Conjugate acid

Conjugate acid-base pair

Conjugate acid-base pair

Acids and Bases

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

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

Strong acid and 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

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

Acids and Bases

C2H5OH C2H5O-H2O OH-HPO4

2- PO43-

HCO3- CO3

2-C6H5OH C6H5O-HCN CN-

NH3NH4+

H2PO4- HPO4

2-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

PhenoxideCarbonatePhosphateHydroxideEthoxide

Hydrogen sulfide

Nitric acidHydronium ionHydrogen sulfate ion

Name of acid Name of ion

Phosphoric acidAcetic acidCarbonic acid

Dihydrogen phosphateAmmonium ion

PhenolBicarbonate ionHydrogen phosphate ionWaterEthanol

Hydrogen sulfide

AcidConjugate Base

IodideChlorideHydrogen sulfateNitrateWaterSulfate

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 an acid or a base.

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

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

base

acid

Acids and Bases

Oxyacids: acidic H is attached to an oxygen atom.

H2SO4 H3PO4 HNO3

Organic acids: contain carboxyl group (-COOH).

They are usually weak.

CH3COOH

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

Ionization of water

pH + pOH = 14

H2O + H2O OH- + H3O+

KW = [H3O+] [OH-] = (1×10-7) (1×10-7)

[H3O+] [OH-] = 1×10-14

[H+] and [OH-]

[H+] = [OH-] Neutral solution

[H+] > [OH-] Acidic solution

[H+] < [OH-] Basic solution

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)

pH of strong acids

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

0.10 M HCl pH = ?

0.10 M HCl 0.10 M H+ and 0.10 M Cl-

[H+] = 0.10 M pH = -log [H+]

pH = -log (0.10) = 1.00

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).

NaOH + HNO3 NaNO3 + H2O

MA × VA = MB × VB

Normality

2NaOH + 1H2SO4 NaSO4 + 2H2O Different coefficients

Equivalent of an acid = amount of an acid that can furnish 1 mol of H+

Equivalent of a base = amount of a base that can furnish 1 mol of OH-

Equivalent weight of acid (base) = mass (g) of 1 equivalent of that acid (base).

HCl 1 equivalent HCl = 1 mole HClequivalent weight HCl = 36.5 g

NaOH 1 equivalent NaOH = 1 mol NaOHequivalent weight NaOH = 40 g

H2SO4 1 mol H2SO4 = 2 mol H+

1/2 mol H2SO4 = 1 mol H+

1 equivalent H2SO4 = 1/2 mole H2SO4

equivalent weight H2SO4 = 98.0/2 = 49.0 g

Normality

H3PO3 1 mol H3PO3 = 3 mol H+

1/3 mol H3PO3 = 1 mol H+

1 equivalent H3PO3 = 1/3 mole H3PO3

equivalent weight H3PO3 = 82.0/3 = 27.3 g

Normality

Normality = Number of equivalents

Volume of solution (L)

Neutralization: number of equivalents of an acid = number of equivalents of a base

NAVA = the number of equivalents of an acid

NBVB = the number of equivalents of a base

NA × VA = NB × VB

[H+] = [OH-]

Buffersacid or base

Buffer

pH stays constant.

Equal molar amount of a weak acid and a salt of weak acid.

Equal molar amount of a weak acid and its conjugate base.

1 mole CH3COOH + 1 mole CH3COONa

1 mole CH3COOH + 1 mole CH3COO-

Buffers

pH of blood = between 7.35 and 7.45

Carbonate buffer H2CO3 / HCO3-

Phosphate buffer H2PO4- / HPO4

2-

Proteins buffer

H2CO3 + OH- → HCO3- + H2O

HCO3- + H3O+ → H2CO3 + H2O

Buffers

HA + H2O A- + H3O+

Henderson-Hasselbalch equation:

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

If [AH] (weak acid) ≠ [A-] (conjugate base)

If [AH] (weak acid) = [A-] (conjugate base)

pH of buffer = pKa of weak acid