Analytical Chemistry 2
Quantitative Analytical Chemistry
Acid base reactions
Part 1
By
Ahmed Hafez, PhD
ahmed.nagib@bue.edu.eg
Marks distribution
Pharm D:
10% coursework / 30% practical (2 exams) / 10% oral / 50% unseen
Pharm D clinical:
15% coursework / 25% practical (2 exams) / 10% oral / 50% unseen
B. pharm:
15% coursework / 30% practical (2 exams) / 10% oral / 15%
Midterm/ 30% unseen
Ahmed Hafez, Acid base reactions
1
Instrumental analysis
Instrument measures a physical
property of analyte
Gravimetric analysis
Weighing the isolated analyte
Volumetric analysis
“Titration”
1- Acid base
2- Complexometry
3- Precipetimetry
4- Redox
Quantitative
What is the sample’s
concentration/amount?
Qualitative
What is the sample’s
name/identity ?
Analytical Chemistry
 Known Concn
Standard
???? Concn
Sample
End Point
Bulb pipette
Transfer
Indicator
Reagent
accurate
volume
Few drops
Ahmed Hafez, Acid base reactions
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Volumetric analysis “Titration”
Advantages
Disadvantages
Economic and do not require
specialized apparatus
Non-selective
Require large amounts of sample and
reagents
Absolute methods .. Do not
dependent on the calibration
of an instrument
Time-consuming if not automated
Robust .. Not affected by minor
experimental variation
Reactions of standard solutions with
the analyte should be rapid and
complete
Analysis can be automated
Ahmed Hafez, Acid base reactions
Precipitating
agent
Precipitation
Ion
Ox.
Red.
Redox
Red.
Ox.
Standard
Classification of reactions in titrimetric analysis
Base
Acid
Neutralization
Acid
Base
Complexing
agent
Complex
formation
Metal
Sparingly
soluble
Sample
3
Requirements of volumetric reactions
The reaction between the sample and the standard must have the
following conditions:
1. Simple reaction (have balanced equation)
2. Single reaction between sample and standard
3. Fast reaction
4. An indicator should be available which, by a change in physical
properties (color or formation of a precipitate), should sharply
define the end point of the reaction
Ahmed Hafez, Acid base reactions
Standard solution Solution of exactly known concentration
Expressions of standard solution
Molar standard solution (M)
Normal standard solution (N)
1 M = 1 Mwt. dissolved in 1 L
1 N = 1 equivalent weight dissolved in 1 L
2 M = 2 Mwt. dissolved in 1 L
2 N = 1 equivalent weight dissolved in 1 L
0.1 M= 0.1 Mwt. dissolved in 1 L
0.1 N= 1 equivalent weight dissolved in 1 L
Equivalent weight = Mwt/n
Empirical standard solution
Special preparation for a certain
analyte
Acid or base
(reactive)
Eq.wt = M.wt / No. of replaceable H+ or OH-
1 mL of empirical solution
reacts with a definite quantity
of the sample
Salt
Eq.wt = M.wt / No. of cations x its valency
Eq.wt = M.wt / No. of anions x its valency
Ahmed Hafez, Acid base reactions
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1M HCl
1M H2SO4
Mwt= 36.5 g
Mwt= 98 g
1M H2SO4 = 1 Mwt in 1 L
= 98 g in 1 L
1M HCl = 1 Mwt in 1 L
= 36.5g in 1 L
1N H2SO4
1N HCl
Eq.wt = M.wt / No.of replaceable H+
Eq. wt= 36.5 g/1 = 36.5
Eq.wt = M.wt / No. of replaceable H+
Eq. wt= 98/2 = 49
1N HCl = 36.5g in 1 L
1N H2SO4 = 1 Eq. wt in 1 L
= 49 g in 1 L
1M HCl = 1 N HCl
1M NaOH = 1N NaOH
1M H2SO4 is 2X stronger than 1N H2SO4
1M H2SO4 = 2N H2SO4
Ahmed Hafez, Acid base reactions
10 ml 0.1 N NaOH reacts with 10 mL 0.1 N HCl
1 OH- = 1 H+
10 ml 0.1 N NaOH reacts with 10 mL 0.1 M HCl
1 OH- = 1 H+
10 ml 0.1 N NaOH reacts with 10 mL 0.1 N H2SO4
1 OH- = 1 H+
10 ml 0.1 N NaOH reacts with 5 mL 0.1 M H2SO4
1 OH- = 2 H+
Solutions with same Normality react by equal volumes
N V = N’ V’
Ahmed Hafez, Acid base reactions
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𝑬𝒒𝒖𝒊𝒗𝒂𝒍𝒆𝒏𝒕 𝒘𝒆𝒊𝒈𝒉𝒕 𝒐𝒇 𝒔𝒂𝒍𝒕 =
𝑴𝒐𝒍𝒆𝒄𝒖𝒍𝒂𝒓 𝒘𝒆𝒊𝒈𝒉𝒕
𝒏𝒐 𝒐𝒇 𝒄𝒂𝒕𝒊𝒐𝒏 𝒐𝒓 𝒂𝒏𝒊𝒐𝒏 × 𝒊𝒕𝒔 𝒗𝒂𝒍𝒆𝒏𝒄𝒚
𝑬𝒒𝒖𝒊𝒗𝒂𝒍𝒆𝒏𝒕 𝒘𝒆𝒊𝒈𝒉𝒕 𝒐𝒇 𝑵𝒂𝟐𝑺𝑶𝟒 =
𝑴𝒐𝒍𝒆𝒄𝒖𝒍𝒂𝒓 𝒘𝒆𝒊𝒈𝒉𝒕
𝟐×𝟏
Or (1 sulfate ×2)
𝑬𝒒𝒖𝒊𝒗𝒂𝒍𝒆𝒏𝒕 𝒘𝒆𝒊𝒈𝒉𝒕 𝒐𝒇 𝑵𝒂𝑪𝒍 =
𝑴𝒐𝒍𝒆𝒄𝒖𝒍𝒂𝒓 𝒘𝒆𝒊𝒈𝒉𝒕
𝟏×𝟏
𝑬𝒒𝒖𝒊𝒗𝒂𝒍𝒆𝒏𝒕 𝒘𝒆𝒊𝒈𝒉𝒕 𝒐𝒇 𝑭𝒆𝟐 𝑺𝑶𝟒
𝟑
=
𝑴𝒐𝒍𝒆𝒄𝒖𝒍𝒂𝒓 𝒘𝒆𝒊𝒈𝒉𝒕
𝟐×𝟑
Or (3 sulfate ×2)
Ahmed Hafez, Acid base reactions
How to prepare standard solutions ?
Primary standard
Direct preparation
If it loses one of the
previous conditions
-High purity
-Stable toward air and CO2 and not absorb H2O
-Soluble in titration medium.
-large Mwt to ↓ weighing error
1ry std acids:
Potassium acid phthalate, Benzoic acid,
Constant-boiling-point HCl
1ry std bases:
Anhydrous Na2CO3, Anhydrous KHCO3
1ry std salts: Mercuric oxide
Secondary standard
NaOH (absorb water-CO2)
HCl (volatile)
Approximate preparation then standardized
against primary standard to calculate the
standardization factor (f)
Ahmed Hafez, Acid base reactions
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f
Standardization factor
(Correction factor)
f=
𝐕𝐨𝐥𝐮𝐦𝐞 𝐨𝐟 𝐬𝐭𝐚𝐧𝐝𝐚𝐫𝐝 𝐨𝐟 𝒆𝒙𝒂𝒄𝒕 𝐜𝐨𝐧𝐜𝐞𝐧𝐭𝐫𝐚𝐭𝐢𝐨𝐧
𝐕𝐨𝐥𝐮𝐦𝐞 𝐨𝐟 𝐬𝐭𝐚𝐧𝐝𝐚𝐫𝐝 𝐨𝐟 𝒂𝒑𝒑𝒓𝒐𝒙𝒊𝒎𝒂𝒕𝒆 𝐜𝐨𝐧𝐜𝐞𝐧𝐭𝐫𝐚𝐭𝐢𝐨𝐧
“f” must be between 0.95 – 1.05
if out of range it must be corrected, i.e., diluted or concentrated.
f Standardization
F Equivalent factor
(correction) factor
1 mL standard ≡ ?? g sample
𝑪𝒐𝒏𝒄𝒏 =
𝐦𝐥𝐬 𝐨𝐟 𝐬𝐭𝐝 ×𝐟 ×𝐅 ×𝟏𝟎𝟎𝟎
=
𝐒𝐚𝐦𝐩𝐥𝐞 𝐕𝐨𝐥𝐮𝐦𝐞 (𝟏𝟎 𝐦𝐥)
mls × f × F =
g in sample
𝒎𝒍𝒔 ×𝒇 ×𝑭
=
𝟏𝟎
g/1ml
g/L
Ahmed Hafez, Acid base reactions
Acid- base
Neutralization reaction
Acid + Base → Salt + Water
Ahmed Hafez, Acid base reactions
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Acid base theories
Arrhenius theory (Ionization theory)
Acid: electrolyte that dissociates to give H+
Neutralization reaction:
H+ +OH- → H2O
Base: electrolyte that dissociates to give OHBronsted lowery theory
Acid : proton donor
Neutralization reaction is transfer of protons
Base: proton acceptor
Acid
Conjugate
base
Ahmed Hafez, Acid base reactions
Acid
Conjugate
base
The stronger the acid , the weaker its conjugate base
The stronger the base, the weaker its conjugate acid
HSO4- is the conjugate base of H2SO4
H2O is the conjugate acid of OHH2O is conjugate base of H3O+
Ahmed Hafez, Acid base reactions
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Amphiprotic (Amphoteric) electrolyte
serve as both a proton donor and a proton acceptor.
H2O + H2O → H3O+ + OH-
Conjugate acid Conjugate base
of H2O
of H2O
+ H+
H2CO3 ⇋ HCO3
Conjugate acid
of HCO3-
+ H+
- H+
-⇋
CO32-
Conjugate base
of HCO3-
- H+
H2SO4 ⇋ HSO4 ⇋ SO42-
Conjugate acid
of HSO4-
Conjugate base
of HSO4-
Ahmed Hafez, Acid base reactions
Acid base theories
Lewis theory
Acid : electron pair acceptor ex. BF3, AlCl3
Base: electron pair donor ex. NH3
Ahmed Hafez, Acid base reactions
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Acid base theories
Ahmed Hafez, Acid base reactions
Electrolytic dissociation
•
•
Non electrolytes: doesn't ionize and doesn't conduct electricity
Electrolytes: dissociate (ionize) and conduct electricity.
Degree of Dissociation
Degree of Ionization
“α”
𝑵𝒐. 𝒐𝒇 𝒅𝒊𝒔𝒔𝒐𝒄𝒊𝒂𝒕𝒆𝒅 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆𝒔
𝑻𝒐𝒕𝒂𝒍 𝒏𝒖𝒎𝒃𝒆𝒓𝒔 𝒐𝒇 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆𝒔 𝒃𝒆𝒇𝒐𝒓 𝒅𝒊𝒔𝒔𝒐𝒄𝒊𝒂𝒕𝒊𝒐𝒏
Strong electrolyte
Weak
electrolyte
α is far from unity (⁓0.0..)
α is near unity (⁓1)
HCl → H+ + Cl-
CH3COOH ⇋ H+ + CH3COO-
NaOH → Na+ + OH-
NH4OH ⇋ NH4+ + OHReversible reaction
Equilibrium exists
Irreversible reaction
Ahmed Hafez, Acid base reactions
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Water is a weak electrolyte
H3O  + OH
2 H2 O
H2 O
H

+ OH
Kw= [H+] [OH-]
K = [Products] / [Reactants]
K=
[ H  ][OH  ]
[ H 2 O]
⁓ =1
Kw ion product of water or water dissociation constant
Kw = [H+] [OH-] = 10-14
In neutral solution, [H+] = [OH-] = 10-7 M (25oC)
In an acid medium
In an alkaline medium
[H+] is > 10-7 > [OH-]
[OH-] is > 10-7 > [H+]
Ahmed Hafez, Acid base reactions
The pH Concept
pH = log 1/ [H+]= -log [H+]
[H+] decreases → pH increases
For a neutral solution [H+] = 10-7
pH = - log 10-7 = 7
In a solution of [H+] = 10-3 M
pH = - log [H+] = - (-3) = 3
pH + pOH = 14
[H+] = 10-4 → pH = 4
[H+] = 10-9 → pH = 9
Ahmed Hafez, Acid base reactions
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pH + pOH = 14
Ahmed Hafez, Acid base reactions
[H+]
[OH-]
pH
pOH
Acidic solution
> 10-7
< 10-7
<7
>7
Neutral solution
10-7
10-7
7
7
Basic solution
< 10-7
> 10-7
>7
<7
Ahmed Hafez, Acid base reactions
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What is the pH and pOH of a solution that is 0.05 M in H+ ?
Solution: [H+] = 5.0 x 10-2 M
pH = - log 5.0 x 10-2 = 1.3
pOH = 14 – 1.3 = 12.7
What is the pH of a solution for which [OH-] = 0.03M ?
Solution: [OH-] = 3.0 x 10-2
pOH = - log [OH-] = - log 3.0 x 10-2 = 1.52
pH = 14 – 1.52 = 12.48
Ahmed Hafez, Acid base reactions
Ahmed Hafez, Acid base reactions
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