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