Chem Eq 3 1

Strong Bases (examples, pH calc.) Acid-Base Theories Weak Electrolites

Strong Bases (examples, pH calc.) Acid-Base Theories Weak Electrolites

Dr. M. Sasvári: Medical Chemistry LecturesDr. M. Sasvári: Medical Chemistry Lectures 3. 3.

Chem Eq 3 2

Strong basesComplete ionization in water

Strong basesComplete ionization in water

BOH B+ + OH-

Chem Eq 3 3

I. II. III. IV. V. VI. VII. VIII.LiNaK

Strong basesStrong bases

Strong bases: RemarksLiOH (Lithium hydroxide) removes CO2 in spacecraft's

NaOH (Sodium hydroxide) oven cleaner, drain openerKOH (Potassium hydroxide) manufacturing liquid soaps

Complete ionization in water

K+ + OH-

Na+ + OH-

Li+ + OH-

Oxidation No.: +1

Chem Eq 3 4

Example:

2K + 2H2O → 2K+ + 2OH - + H2

KOH is a strong base its formation: exergonic reaction

heat → H2 gas ignites

Chem Eq 3 5

I. II. III. IV. V. VI. VII. VIII.

CaSrBa

Strong basesStrong bases

Strong bases: RemarksCa(OH)2 (Calcium hydroxide) slaked lime (used in mortar)

Sr(OH)2 (Strontium hydroxide)Ba(OH)2 (Barium hydroxide) X-ray of the stomach

Complete ionization in water

Sr2+ + 2OH-

Ba2+ + 2OH-

Ca2+ + 2OH-

Oxidation No.: +2

Chem Eq 3 6

NaOH Na+ + OH-

Ca(OH)2 Ca2+ + 2 OH-

n = 1

n = 2

Normality = Molarity * n (number of dissociable OH-)

1 N strong base contains 1 mol of OH - per liter

Normality of a strong base = the [OH -] of the solution

Chem Eq 3 7

pH of a strong basepH of a strong base

[OH-] = [ strong base] in Normality[OH-] = [ strong base] in Normality

[OH-] from water is negligible [OH-] from water is negligible H+ from waterH+ from water

KOH + OH-K+

H2O H+ + OH-

Chem Eq 3 8

ExamplesExamples KOH (N) pOH pH

pH of a strong basepH of a strong base

1 =10 0 00.1 =10-1

0.01 =10-2

0.001 =10-3

=10-8 pOH < 7

The pH of a base is always above 7! The pH of a base is always above 7!

pOH = - lg [OH-]= -lg cpOH = - lg [OH-]= -lg c

strong base (N)strong base (N)pH = 14 - pOHpH = 14 - pOH

141 132 123 11

pH > 7

[OH-]from H2O: 10-7 M[OH-]from KOH: 10-8 M

Total [H+] > 10-7 M

Chem Eq 3 9

4 g NaOH (Mw=40) is dissolved in water upto a total volume of 500 ml. What is the pH of the solution?

mol =g

Mw

4

40= = 0.1 Molarity =

mol

L

0.1

0.5= = 0.2 M

0.2 N

pOH= -log10 (0.2)= 0.7BASE!

pH= 14-0.7=13.3

10-2.3 = 0.005 N

0.005 M

BASE! pOH= 14 – 11.7 = 2.3

What is the M and N of the NaOH solution with pH 11.7?

Chem Eq 3 10

Acid-Base Theories

The Bronsted-Lowry Theory

Chem Eq 3 11

INIINIINIINI

EQEQ

An acid, when dissolved in water, increases the [ H+](decreases pH) decreases [OH-] (increases pOH)

H2O H+ + OH-

The Arrhenius concept (1884)The Arrhenius concept (1884)

A base, when dissolved in water, decreases the [ H+](increases pH) increases [OH-] (decreases pOH)

[H+] [OH-] [H+] [OH-]

H2O H+ + OH-

ACID added

H2O H++ OH-

BASE added

Chem Eq 3 12

Base = accepts a proton in a proton-transfer reaction

The Bronsted-Lowry conceptThe Bronsted-Lowry concept

Acid = donates a proton in a proton-transfer reaction

ACID Conjugated base

AH

+ HA-AH

+ HA-

BH

+ HB BH

+ HBBASE Conjugated acid

Chem Eq 3 13

Protonated forms

AH

BH

+ HB

+ HA-

Deprotonated forms

Bases Conjugated bases

Acids Conjugated acids

Chem Eq 3 14

Deprotonated formsDeprotonated formsProtonated formsProtonated forms

ExamplesExamples

ACID

Acetic acidCH3COOH

Conjugated BASE

Acetate ion

CH3COO-+ H+

BASE

ammonia

NH3 + H+CONJUGATED ACID

NH4+

ammonium ion

Chem Eq 3 15

N::

::

H

HH + H+ N:

:

::

H

HH H

+

ammonium ion

NH3

donatesan electron

pairLewis base

NH3

donatesan electron

pairLewis base

H+ accepts

an electron pair

Lewis acid

H+ accepts

an electron pair

Lewis acid

The Lewis conceptThe Lewis concept

NH3 + H+ NH4 + example:

ammonia

Chem Eq 3 16

example:+ Cu2+4 NH3 [Cu(NH3)4]2+

ammonia copper(II)ion Tetraamminecopper(II) ion

Complex ion (coordination compound)

Complex ion (coordination compound)

The liganddonates

an electron pair

Lewis base

The liganddonates

an electron pair

Lewis base

The central metal ion accepts

an electron pair

Lewis acid

The central metal ion accepts

an electron pair

Lewis acid

+ Cu2+

Cu :NH3H3N:NH3

:

NH3:

2+N::

::

H

HH4

Chem Eq 3 17

Weak electrolites- Degree of ionization ()

- pKa, pKb

- Strength of Acidity/Basicity

Weak electrolites- Degree of ionization ()

- pKa, pKb

- Strength of Acidity/Basicity

Chem Eq 3 18

Degree of IonizationDegree of Ionization

INIINI

CH3COOH + H2O CH3COO- + H3O+

(2-0.006) M 0.006 M 0.006 M

1M (excess)

acetic acid

Endergonic process, reaction goes backwardsacetate ions will be protonated by the hydroxonium ion

0.006 M of the ionized forms remain in the new EQ

1M

acetate ion

1M

hydroxonium ion

= 0.006 2 = 0.003Degree of ionization () in the EQ:

EQEQ

0 < < 10 < < 1moles in ionized formtotal number of moles

=

Chem Eq 3 19

The [H+] concentration of a 0.01 M monoprotic acid solution is 10 -4. Calculate the degree of ionization!

= [H+]

c=

10 -4

0.01= 0.01 or 1%

The [OH -] concentration of a 0.02 M base solution is 10 -3. Calculate the degree of ionization!

= [OH-]

c=

10 -3

0.02= 0.05 or 5%

Chem Eq 3 20

2 c

1 - Ka =

Acidic Ionization Constant (pKa)Acidic Ionization Constant (pKa)

Ka =(0.006)2

(2-0.006)=1.8 10-5

acidacid

Ka =

CH3COOH CH3COO - + H+

Ka =c)c)

c - c)

Degree of Ionization () and the Ionization constant (Ka):

c = total concentration (HA + A-)

Ka is an equilibrium constantof acidic dissociation

(concentration of H2O included)

Chem Eq 3 21

Will the change if we dilute a weak acid?

higher dilution more complete ionization

AH + H2O A- + H3O+

will

= 1.3 % = 4.2 %

Ka = 1.7 10-5

Ka change!

2 c

1 - Ka =

0.1 M 0.01 M

increase

does not

Chem Eq 3 22

Basic Ionization Constant (pKb)Basic Ionization Constant (pKb)

NH3 + H2O NH4+ + OH -

basebase

Kb =

Kb is an equilibrium constantof basic dissociation

(concentration of H2O included)

KOH K+ + OH -in general:

2 c

1 - Kb =

Chem Eq 3 23

pK < 2

K > 10 -2

the higher is the pKa/pKb

the weaker is the acidity/basicity

weak acidsweak bases

conjugated acidsconjugated bases

Strength of Acidity/Basicity Strength of Acidity/Basicity

Strong acidsand bases

2 4 7 pKa