first & second&third lectures acid base (1&2&3).pdf
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INTRODUCTION
"
Pharmaceut ical Analyt ical Chemist ry 1
Co u r se Co d e : 1 8 0 5 3 2 3
Lec tu re r : Dr. Afa f Osman
Co u r se S c h e d u l e :
L e c t u r e : T h u r sd a y 3 rd & 4 t h
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References:
Analytical Chemistry, Gary D. Christian, Publisher: Wiley; 6th edition.
Fundamentals of Analytical Chemistry, Douglas A. Skoog, Donald M. West, F. James
Holler, Stanley R. Crouch, Publisher: Brooks Cole; 8th edition.
Recommended reading / resources
Analytical chemistry, An introduction, Douglas A. Skoog, Donald M. West, F. James
Holler, Stanley R. Crouch, Publisher: Brooks Cole; 6th edition.
Dean's Analytical Chemistry Handbook , Pradyot Patnaik, Publisher: McGraw-Hill
Professional.
Quantitative Chemical Analysis , Daniel C. Harris, Publishers: W.H. Freeman and
Company;8th Edition.
#
Methods of Assessment:
Mid-Term Exam 20%
Final exam 50% (out of 60% in case of only theory courses)
Laboratory work, presentation and seminars 20%
Other academic activities 10% (20% in case of only theory courses)
Pass Requirements
The aggregate mark must surpass the pass/fail boundary, which is 60%.
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Quantitative analysisQuantitativeanalysis deals with the determination of the quantityof the
substance to be analyzed.
Methods of quantitative analysis may be classified according to:
1- The quantity measured,2- Physical state of the substance to be analyzed and
3- The process of measurement.
Classification according to the quantitymeasured
Macro-analysis Semi-microanalysis
Micro-analysis
Measuring quantity starting
from 100mg and more
Measuring quantity ranging
from 10-100mg
Measuring quantity
not exceeding 1mg
Classification-according to the physical state of the substanceto be analyzed.
Gas
analysis
Food analysis Water analysisSubstance in gaseous state
Kind of the analyzed material
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%
Classification according to the processof measurement
Volumetric analysis Gravimetric analysis Instrumental methods of analysis
Neutralization reactions Formation weakly ionisable salt Complexation reactions
Electron transfer reactions
Formation of water Displacement titration
Formation of weak acid Formation of weak base
Gravimetric analysis: It is a quantitative method of analysis by weighing the final product of reaction
after its isolation in pure and stable form of definite chemical structure.
Instrumental methods of analysis: Are physico-chemical methods, depend mainly on optical and electrical properties. By measuring these
properties which are quantitatively related to the analyzed sample, we can find its concentration.
e.g Spectrophotometric, Potentiometric and Conductometric Methods of Analysis. 9/22/2014
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&
Vo l u m e t r i c A n a l y s i s : Depends on measuring the volume of the analyzed sample and the volume of standard
solution used for complete reaction.
This process is known as T i t r a t i o n . Which means the capacity of the sample to
combine with the suitable standard quantitatively through quantitative reaction. Q u a n t i t a t i v e r e a c t i o n , is that reaction which proceed forward to produce
stable products such as weakly ionisable compounds, H2O, weak acid, weak base,
sparingly soluble salts (Precipitate), complex ion, etc.
Volumetric Analysis Classified Into The Following Types:
A- N e u t r a l i z a t i o n r e a c t i o n s :1- Formation of water
Water is produced as a result of interaction between acid and base, which involves
combination between hydrogen ion and hydroxyl ion to form very weakly ionisable
water.
Acid + Base
Water + Salt
H++ OH- H2O
2- Displacement titration:
a- Formation of weak acid.
Salt of weak acid + strong acid
weak acid + salt of strong acid.
KCN + HCl
HCN + KCl
Na2B
4O
7.5H
2O + 2 HCl
4H3BO
3+ 3NaCl.
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'
b- Formation of weak base:
Salt of weak base + Strong base weak base + salt of strong base
AlCl3+ 3 NaOH AL(OH)3+ 3 NaCl
NH4Cl + NaOH NH4OH + NaCl
B. F o r m a t i o n w e a k l y i o n i s a b l e s a l t : { ppt} :
Reaction between mercuric nitrate (Hg(NO3)2) or AgNO3 with Cl-.
Ag+ + Cl- AgCl (weakly ionised)
Hg(NO3)2+ 2NaCl HgCl2 (weakly ionised) + 2 NaNO3
C. C o m p l e x a t i o n r e a c t i o n s :
Reaction between silver ion (Ag+) and cyanide ion (CN-) to produce the weakly ionised
complexion, soluble K[Ag(CN)2]
Ag++ 2 CN-
[Ag(CN)2]-
Reaction between EDTA (H2y2-) and metal ion e.g. Ca2+to produce the weakly ionised
complex orchelate (Cay2-)Ca2+ + H2y
2-
Cay2-+ 2H+
D. E l e c t r o n t r a n s f e r r e a c t i o n s :
Transfer of electrons between reactants (oxidants and reductants) which is followed by
change in the oxidation number of the reactants.
Ce4++ Fe2+
Fe3++ Ce3+9/22/2014
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Requirements of Titrimetric Reactions:
1. The reaction must be simpleand can be expressed by chemical equation.
2. A single reaction must occur between the desired sample and titrant as described by
corresponding chemical equation.3. The reaction must be instantaneous. If slow it must be catalyzed.
4. Suitable standard solution must be available as titrant.
5. The end point should be easily detected by visual indicator or an instrumental
method.
Volumetric methods are more commonly used as they are more quicker and easiermethods if compared with gravimetric and physico-chemical methods.
In volumetric analysis we deal with the determination of the concentration of
solution of a certain sample or the percentage of pure chemical in powdered
sample. This can be achieved by the use of solutions of known concentrations,
which are known as standard solutions.
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S d d S l i
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S t a n d a r d S o l u t i o n s
They are solutions of exact and known concentration. They are classified according to the type
of concentration into:
1 . M o l a r So l u t i o n ( M )
It is a solution of known concentration, each liter of which contain the gram molecular weight
orfraction of the gram molecular weight ormultiple of the gram molecular weight. When the concentration is:
Molecular weight (M.wt) / liter (L), it is expressed as 1M or M
M.wt /L, it is expressed as M/2 or 0.5M solution.
4 M.wt/L, it is expressed as 4M solution.
M= n / v = no. of moles/ volume (L) = no. of millimoles / volume ( ml)
= wt(g) / MWV(L) = wt mg/ MWV (ml)
2. N o r m a l S o l u t i o n ( N )
It is a solution of known concentration, each liter of which contain the gram equivalent weight
(eq.wt) orfraction of the gram eq.wt ormultiple of the gram eq.wt.
When the concentration is:
eq.wt / L, it is expressed as 1N or N solution.1/ 10 eq.wt / L, it is expressed as 0.1N or N/10 solution.
3 eq.wt / L, it is expressed as 3N solution.
N = no. of equivalents/ Volume (L) = no. of milliequivalents / Volume (ml)
= Wt (g) / eq.wt. V L = Wt. (mg) / eq. wt. V ml 9/22/2014
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Calculation of The Equivalent Weight of Different Electrolytes
Acids
Eq.wt = (M.wt ) / number of replaceable hydrogen
i.e. in case of :
HCl, eq.wt = M.wt / 1
H2SO4, eq.wt = M.wt / 2
Bases
Eq.wt = (M.wt ) / number of replaceable hydroxyl ion
i.e. in case of :
NaOH, eq.wt = M.wt / 1
Ba(OH)2
, eq.wt = M.wt /2
Salts
Eq.wt = M.wt / number of cations its valency
Or M.wt / number of anions its valency
i.e. in case of
Na2SO4, eq.wt = M.wt / 21 or M.wt / 1 2
P r e p a r a t i o n o f s t a n d a r d s o l u t i o n s
a. Direct method: {A chemical is of p r i m a r y standard quality}
An accurately weighed amount of the solute is transferred into a
volumetric flask, dissolved in the solvent then completed to the
required volume and mixed well. The prepared solution is used as
exact standard.9/22/2014
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P r i m a r y S t a n d a r d C h e m i c a l s
Primary standard chemicals are substances of definitely known composition and high
purity.
They must fulfill the following requirements:1. They must be available in very high grade of purity and of known composition(A.R)
2. They must be easily tested for impurity by simple test.
3. They must be stable, i.e. not absorbing water (not be hygroscopic) or CO2from
atmosphere, not volatile and withstand drying at 110-120oC.
4. They must react with other substancesquantitatively according to a balanced chemical
equation. i.e. react stoichiometrically.
5. They must be readily solublein the solvent.
6. They should have high equivalent weight to minimize weighing error.
Examples of primary standard chemicals:
Potassium hydrogen phthalate (KHC8
H4
O4
), benzoic acid (HC7
H5
O2
), constant-boiling-
point hydrochloric acid, anhydrous sodium carbonate (Na2CO3), anhydrous potassium
bicarbonate (KHCO3)and mercuric oxide (HgO). potassium dichromate (K2Cr2O7)
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b. Indirect method:
If the solute is not primary standard, it is used to prepare solution of approximate
concentration [secondary standard solution], and its exact concentration is determined
by a process known as Standardization against primary standard solution.
Standardization factor (f) = volume ofexact standard / volume of approximatestandard
= volume ofknown normality / volume of unkown normality
f express, how much of exact is present in the approximate.
f ranges from 0.95-1.05, out this range the solution is not of expected strength.
- The volume of secondary standard must be multiplied by its standardization
factor (f ) to obtain the volume of St. soln. of exact normality or molarity.
S e c o n d a r y S t a n d a r d C h e m i c a l s
Secondary standard chemical is a standard that is prepared in the laboratory for a
specific analysis and whose content have been found by comparison against primary
standard.
Examples of secondary standard chemicals:e.g. borax (Na2B4O7.10H2O) and oxalic acid (H2C2O4.2H2O).
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HCl
NaOH
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What volume of a 0.1 M HCl solution is needed to neutralize 25 mlof 0.35 M
NaOH ?
HCl + NaOH NaCl + H2O
M = n / V
n = number of moles
V = volume
n = V M
Number of moles of NaOH = 25 0.35 = 8.75 mmoles
n of NaOH = n of HCl since reaction is 1 : 1 = 8.75 m mloes
M V of HCl = 8.75
0.1 V = 8.75 V = 87.5 ml
N1 V1 = N2 V20.1 V1 = 0.35 25
V1 = 87.5 ml
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#$%&'()*&+,*-./(0#1(.#234&5#./(.#23)&
!"#$%&'() +#+,'+#-.( /. !01)-1(2)$#13&&
"%
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! #$ 4 & 56 #
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!"#$( 4 &'()(56)-,#)(Acids:
Arrhenius acid: Any substance that, when dissolved in water,increases the concentration of hydronium ion (H3O
+) or Substances which
ionize to give H+ionsin solution. (H2SO4 & HCl)
Bronsted-Lowry acid: A proton donor i.e substance which lossor donate proton
Lewis acid: An electron acceptor i.e. accept lone pair of electrons.(AlCl
3
, BF3
)
Bases:
Arrhenius base: Any substance that, when dissolved in water,increases the concentration of hydroxide ion (OH-) orSubstances which ionize
to give hydroxide ions(OH-) in solution. (NaOH)
Bronsted-Lowery base: A proton acceptor i.e substance whichgains or accepts proton
Lewis base: An electron donor i.e donates lone pair of electrons.
( NH3, amines)
"&
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theory (Electrolytic Dissociation Theory) :Arrhenius-1
Acid: Is the substance which ionize to give H+ eg. HCl
Base: Is the substance which ionize to give OH- eg NaOH
There are some points of weakness in electrolytic dissociation theory as:
acidic properties on dry litmus papernohasgas-HCl
base-base according to the Arrhenius acidnotare,2NH-Rand amines3NHAmmonia
theory. Since there is no hydroxyl group present in the ammonia (NH3) molecule, But
ammonia shows basic nature
Ammonia reacts with the water it is dissolved in to produce ammonium ions and
hydroxide ions:
NH3 + H2O NH4OH NH4+ + OH-
i.e. the basic characters are due to the formation of compounds which release OH- .
.anhydrous basesare described asammonia and aminesTherefore
This theory didn't discuss the role of solvent in the ionization process.
"'
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is very small in size, its+Hbe liberated.+During dissociation of an acid in water, H
electric charge is very intense, therefore, it cannot exist independently in solution. It
oftwo unshared pairoxygen of water, due to the presence ofattracted towill be
electrons.
Electric charge (F)
Q/m
Where: Q = charge m = radius of mass.
Fin case of H+is very intense, due to its very small radius thereforeprotons are
hydrated or generally solvated with solvent molecules
H+ + H2O: H3O+ hydronium ion
theoryArrhenius-1
Acid
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- The solvent, in this theory, is involved in the reaction as acid or base,
-Every acid has a conjugate base and the base has conjugate acid.
- Thestronger the acid the weaker its conjugate base and vice versa.
- Waterbehaves as acid or base because it is neutral (amphoteric)
Lowry theory :-Bronsted-2
Acid: Is the substance which donate proton.
Base: Is the substance which accept proton.
Eg. HCl + H2O Cl- + H3O
+
Acid base conj. base conj. acid
Eg. NH3 + H2O NH4+ + OH-
base acid conj. acid conj. base
.B.N
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HA + B- A- + BH
acid baseconjugatebase
conjugateacid
BRONST ED - LOWRY THEORY
+H+-H+
acid = proton donor
base = proton acceptor
When an acid gives up a proton, the remaining species has a certain proton affinity and hence
is a base. This base known as the conjugate base of the acid, and the two forms are known as
an acid-base pair.
"*
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#+
!"# %&'() *"# +,-./01*# 21)# ,3 *"# 1+(4 5%&6
!"# 7+'() *"# +,-./01*# 21)# ,3 *"# 1+(4 57+'1-4
!"# 5895:
;8< () *"# +,-./01*# 1+(4 ,3 *"# 5=
;>
!"# )*?,-0#? *"# 1+(46 *"# @#1A#? (*) +,-./01*# 21)# 1-4 B(+#
B#?)1>
Acid (A1) Base(B2) Conj-Acid(A2) Conj-Base(B1)HCl + H2O H3O
+ + Cl-
NH4+ + H2O H3O
+ + NH3
HSO4- + H2O H3O
+ + SO42-
Base1 Acid2 Conj-Base2 Conj-Acid1
NH3 + H2O OH- + NH4
+
CH3COO- + H2O OH
- + CH3COOH
HPO42- + H2O OH
- + H2PO4-
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Conjugate Acid Base Pairs
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Conjugate Acid-Base Pai rs
#"
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##
Classificationof Acids and Bases According to Bronsted- Lowery Concept
Acids.
Neutral molecules
(uncharged acids)
Charged acids
e.g. HCl, H2SO4,
HClO4
CH3COOH, HCOOH
Anionic acids.
e.g. HSO4-, H2PO4
-Cationic acids
e.g. NH4+and
Onium cations of
amines,
e.g. R-NH3+
, R2-NH2+
and R3-NH
+
Bases
Neutral molecules(uncharged bases)
e.g.NH3, R-NH2,
R2-NH, R3-N
Charged bases
(Anionic bases)
e.g, CH3COO-,
HCOO-,
C2O42-,Cl-, SO4
2-,NO3-
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Acid : Is substance which accept lone pair of electrons eg. BF3, AlCl3.
Base: Is substance which donate lone pair of electrons eg NH3, amines.
Neutralizationis the sharing of an electron pair between an acid and base and form
This may be followed by ionization..covalent bonda coordinate
H+Cl-+ :NH3 NH4+Cl- NH4
+ + Cl-
Co- ordinate bondL . acid L . base
Adduct
contain atom with unshared-pair of electrons e.g., N,O,S,P
Lewis theory :-3
is not essential-OHor+Hthe presence ofAccording to Lewis theory,
- Ammonia (NH3) is a base although does not contain no OH-
- Borontrichloride is a Lewis acid although contain no H+atoms
#$
T h e L a w o f M a s s A c t i o n
http://en.citizendium.org/wiki?title=Covalent_bond&action=edit&redlink=1http://en.citizendium.org/wiki?title=Covalent_bond&action=edit&redlink=1 -
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#%
T h e L a w o f M a s s A c t i o n
The velocity of a chemical reaction is proportional to the product of the active masses
{concentration in gram /mols} of the reacting substances
A+B C+D(f)
(b)
The velocity of the forward reaction (f) depends on the concentration of both A and B, where;
Vf[A] [B] or Vf = Kf[A] [B]
Kfis the velocity constant of the forward reaction, square brackets [ ]are used to denote the molar
concentration.
Vb= Kb[C][D]
Kbis the velocity constant of the backward reaction (b).
At equilibrium, the velocities of the forward and backward reactions will be equal.
Vf = Vb
Kf [A][B] = Kb [C][D]
K = Kf/ Kb = [C][D] / [A][B] K= equilibrium constant at constant temperature."
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Example The Degree Of Dissociation Of:
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#'
HCl H++ Cl- 0.92
HNO3 H++NO3
- 0.92
CH3COOH H+
+ CH3COO-
0.013
H3BO3 H++H2BO3
- 0.001
NaOH Na++OH- 0.91
NH4OH NH4++ OH- 0.013
NaCl Na++ Cl 0.86
CH3COONa Na++CH3COO
- 0.80
CuSO4 Cu2+SO4
2- 0.39
HgCl2
Hg2++2Cl- 0.01
Example The Degree Of Dissociation Of:
HClis a strong acid i.e. its ionization is complete
HCl + H2O H3O+ + Cl-
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A c i d - b a s e E q u i l i b r i u m I n Wa t e r
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#(
A c i d - b a s e E q u i l i b r i u m I n Wa t e r
The equilibrium, which exists in a dilute solution of an acid, like acetic acid (HAc) at
constant temperature:
HAc H+ + Ac-
Applying the law of mass action:
"K" is theionization constant or dissociationconstant of the acid, or acidityconstant,
usually written Ka
A c i d - b a s e E q u i l i b r i u m I n Wa t e r
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#)
A c i d - b a s e E q u i l i b r i u m I n Wa t e r
When a polybasic acid {An acid with more than one replaceable hydrogen atom}
dissolved in water, the various hydrogen atoms undergo ionization to different extents.
H2A H++ HA-
HA- H++ A2-
Applying the law of mass action:
[H+] [HA-] / [H2A] = K1 [H+] [A2-] / [HA-] = K2
K1and K2are known as theprimary and secondary dissociation constants, respectively.
The greater value of K1relative to K2the smaller be the secondary dissociation, and
the greater must be the dilution before the letter becomes appreciable.
The stronger the acid the larger the acidity constant. For a completely ionised acid, the
acidity constant is assumed to be =1moderately Strong acid H3PO4 H2PO4
-+ H+ (Ka1=1.1X10-2)
A weak acid H2PO4- HPO4
2-+ H+ (Ka2=1.1X10-7)
Extremely weak acid HPO42- PO4
3-+ H+ (Ka3=3.6X10-13)
T h e D i s s o c i a t i o n o f Wa t e r
-
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#*
T h e D i s s o c i a t i o n o f Wa t e r
The dissociation of water is an endothermicprocess, it, therefore, increases with
temperature.
Applying the law of
mass action:
"#$ "%% $"&
Kw
is the ionic product of water and is = 1x10-14 at 25oC.
Since, water is weakly dissociated, the value of H2O is considered unity.
The "%ion and $"&ion concentrations are equal in pure water, i.e.,
01.2 3 04152 3 676859 :*+ ;
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Which doesn't ionize and
doesn't conduct electricity.
Dissociation of water
H2O H++ OH-
Dissociation const. Kw = [ H+] [OH-] / [H2O]
- Since H2O is weakly dissociated , therefore H2O is considered unity.
therefore Kw = [H+] [OH-] = 10 -14 at 25oc
Kw : it is called ionic product of water. At 25oc [H+] = [OH-] = 10-7
If [H+] = [OH-] , therefore soln. is neutral
If [H+] > 10-7eg 10-6, 10-5, therefore soln. is acidic
If [H+] < 10-7eg 10-8, 10-9, therefore soln. is alkaline.
base titration in aq. medium-Acid
Solns. are classified into
Electrolytes
Which dissociate(ionize) and
conduct electricity.
Non electrolytes
$+
H y d r o g e n I o n E x p o n e n t p H "
-
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$"
H y d r o g e n I o n E x p o n e n t p H
pH = - log [H+]
pOH = - log[OH-]
[H+] [OH-] = Kw = 10-14
(at 25oC) -log[H+] + -log [OH-] =- log Kw = - log 10-14
pH + pOH = pKw = 14
The pH of pure water = - log 10-7 = 7.
In neutralsolution the pH or pOH = 7.
Acidic solution have pH values less than 7, while alkaline solutions have pHvalues greater than 7.
A pH increase of one unit corresponds to a tenfold decrease of [H+].
pK w = pH + pOH = 14pH = 14 - pOH
pOH = 14 - pH9/22/2014
- log = p
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pH = -log [H+]
i.e. If [H+] = 10-7 pH = - log 10-7= 7
In acidic side i.e. If [H+] = 10-6 pH = - log 10-6= 6
In basic side i.e. If [H+] = 10-8 pH = - log 10-8= 8
i.e. as pH value inc. [H+] conc. decrease.
Acidsoln has pH less than 7 ,
Alkalinesoln. has pH more than 7
Neutral soln. has pH = p OH = 7
Hydrogen exponent : pH
Therefore
- log = p
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*"# C5 )/44#- ?()#) *, Q>
!"# (-(*(1& 144(*(,- ,3 *"# *(*?1-* *, *"# 1+(4 4,#) -,* C?,4/+#
&1?0# +"1-0#)> !"() ?#&1*(B#&V 3&1* ?#0(,- ,3 *"# C5 +/?B# (>#
*"# C5 ,3 *"# ),&/*(,- ?()#) B#?V )&,@&V
!"# C5 ,3 *"# ),&/*(,- ?()#) B#?V )&,@&V/-*(& __>_
,3 *"# 1+(4 "1) 2##- -#/*?1&(]#4>
744(-0 G>F M& 1&A1&(6 *"# M#4(/M 2#+,M#) 1&A1&(-#
1-4 101(- *"# C5 ?1C(4&V ?()#) *, 12,/* FG>
that any indicator with a colorthe change in the pH is so rapid near the equivalence point
change interval between pH 3.5 and 10.5 could be used without much error.
The indicator of choice is that has a transition range in the vertical part of the curve i.e.
M.O (3.3-4.4), phph (8.3- 10.3), bromothymol blue ( 6 - 7.6).
!"#$$&'()*+"*),- ,.0
Select / what is the indicator of choice is that has a transition ??
Very sharp changein pH on additionof less than half adrop of NaOH
&+
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[' T#1A 7+(4 ' X*?,-0 21)# !(*?1*(,-L #>0> %5:%;;5 1-4 Y1;5 21)(+ )1&*
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B (,C;4# AE C4 */ E0I
5
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&$
when18 ml of alkali has been added
C5 I P>QP 8 &,0 FE^= I P>QP 8 G>\: I R>:Q
:' 7* *"# #b/(B1-+# C,(-* '0#0 ,/-#$ ,))'.1 AE C4 */ 5,?c> () 1* *"# 1&A1&(-# )(4# 1-4 12?/C* +"1-0# (- *"# +/?B# () 3?,M Q FF6
(-4(+1*,?>-,* )/(*12, U>; 1-4 U>d 1?#
[/33#? ?#0(,- K57H1-4
+,-./01*# 21)# 1?# I +,-+>
C5 +"1-0#) )&,@&V
Strong base
Weak acid7
9
%' T#1A [1)#'X*?,-0 7+(4 !(*?1*(,- #>0> Y5:1-4 5%& 1+(4(+ )1&*
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&&
!"# *(*?1*(,- ,3 FGGM& G>FY
1MM,-(1 @(*" G>F Y
"V4?,+"&,?(+ 1+(4 ),&/*(,- eCS2 I P>QP
F'J-(*(1& C5:G#/*$# -'-$,-'*. '( )7# -* (,C;4#@#1A 21)#)8
(") (*+ & , (*- + (.- /C5IFP ' WCS2' WC%2 I FP ' =>:Q G>R I FF>F:
=' `/?(-0 *(*?1*(,-L
N HCl has been added0.1ofml90When
C5 IFP ' CS2' &,0 K)1&*H^K21)#H
`/?(-0 *(*?1*(,- Y5P;5 8 5 %& Y5P%& 8 5=;
9f,?M1*(,- ,3 21)(+ 2/33#?< @#1A 21)# 1-4 (*) )1&*
C5 I FP ' P>QP ' &,0 _G^FG I E>:F
:' 7* *"# #b/(B1-+# C,(-* '0#0 ,/-#$ ,))'.1 DEE C4 */ E0D5
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&'
Cl4of weak base and strong acid, NHsaltonly presentis neutralized andOH4All NH
C5IWCS@' WCS28 WC%)I Q ' =>:Q 8 G>R I R>F:
P' 73*#? #b/(B1-+# C,(-* '0#0 -"# (*47-'*. .*F +*.-,'.( #H+#(( :
Salt formed is acidic, hence, equivalence point
comes at a pH < 7.At the very beginning of the curve, the pH starts
by falling quite quickly as the acid is added, but
the curve very soon gets less steep ( due to buffer
action).
!"# ?1-0# ,3 *"# (-4(+1*,? 31&& @(*"(- 9: ' \>R< )/+" 1)
M#*"V& ,?1-0# 9:>:' P>P< ,? M#*"V& ?#4 9P>P' \>:
weak acid (CH3COOH) v. weak base (NH3)
`' T#1A 7+(4'@#1A 21)# !(*?1*(,-6 #>0> Y5:1-4 %5:%;;5!"# +"1-0# (- C5 -#1? *"# #-4C,(-* 1-4 4/?(-0 *(*?1*(,- () B#?V 0?14/1& (>#> -, )/44#-
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Ph.ph.
LITMUS
M.O.
NOTHING SUITABLE
There is no suitable indicator- none change in the vertical portion.
.a pH meterThe end point can be detected by plotting a curve using
!"# +"1-0# (- C5 -#1? *"# #-4C,(-* 1-4 4/?(-0 *(*?1*(,- () B#?V 0?14/1& (>#> -, )/44#-
+"1-0# (- C5 1-4 "#-+# -, (-4(+1*,? +1- 2# /)#4 *, 4#*#+* #-4 C,(-* ,3 )/+" *(*?1*(,->
Application of Neutralization Reactions
' " / ) ' ' ')' G G ' ' )7 (4(
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&)
'( -"# ;$*+#(( */ )#-#$C'.'.1 ,+')'+ (7G(-,.+#( GK -'-$,-'*.2 ,.)7+(4(M#*?V-'( -"# ;$*+#(( /*$ )#-#$C'.'.1 ,4L,4'.# (7G(-,.+#(2 ,.) G*-" ,$# .#7-$,4'M,-'*.7&A1&(M#*?V'
;$*+#((#(.'() /)#3/& 3,? L`(?#+* !(*?1*(,- U#*",4'F
7' X*?,-0 1+(4 [' X*?,-0 21)#%' T#1A 1+(4 ,? 21)# (3 S1 1-4 S2 -,* )) *"1- FG'Q
`#*#?M(-1*(,- ,3 7+(4)'7
F' If the acid is strong can be titrated against strong alkali in presence of M.O or ph.ph.
M.O.notandph.phit is necessary to useweak acidsn determination ofI
2- Acids possessing limited solubility in water, e.g.benzoic, salicylic acids, should first be
dissolved in neutralized ethanol. Water is then added and titrated with NaOHtoph.ph. end point.
3- [,?(+ 1+(4,+-( ,( , F#,L C*.*G,('+ ,+')2 &, J I0N H DE@DE
O- +,. .*- )'$#+-4K -'-$,-#) F'-" (-,.),$) 5,?< G7- -"# ,))'-'*. */ *$1,.'+ ;*4K"K)$*HK
#.",.+# -"# ,+')'-K2 )#H-$*(# *$ '.=#$-#) (71,$ F"'+" F'44C,..'-*4+*C;*7.)( ,( P4K+#$*425,?
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polyprotic acids (H3PO4)
Di t tit ti f h h i id t ib i id i i ibl ith i di t
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pH of Na3PO4 = 12Step 3
pH of Na2HPO4 = 9.6
ph.ph. Step 2
pH of NaH2PO4 = 4.4M. O. Step 1
pH of H3PO4 = 1.5
Just two inflection point
Direct titration of phosphoric acid, as a tribasic acid is impossible with any indicator
as Ka3is very small, 2.2x10-13. Such titration, therefore, may be done indirectly.
Phosphoric acid is replaced by an equivalent amount of HCl by adding neutral CaCl2.
The liberated equivalent amount of HCl is then easily titrated.
2 H3PO4 + 3 CaCl2 Ca3(PO4)2 + 6 HCl
Titrated with NaOH
: `()C&1+#M#-* !(*?1*(,-)
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'#
:' `()C&1+#M#-* !(*?1*(,-)
J* () /)#4 3,? *(*?1*(,- ,3 N1)(&V 5V4?,&V)12 X1&*)
F' Salts from a strong base and a weak acid, e.g.potassium cyanide, borax and sodium carbonate.
2- Salts from a strong acid and a weak base, e.g., ferric chloride and aluminum sulfate.
a - S a l t s f r o m a s t r o n g b a s e a n d a w e a k a c i dL
7' S%Yin water hydrolysis S%Y8 5=; 5%Y 8 S88 ;5'
;- 144(-0 5%& *"# ?#1+*(,- *1A#) C&1+# @(*" *"# ;5'C?,4/+#4 2V "V4?,&V)()6
S%Y 8 5%& 5%Y 8 S%&6"# .#- $#(74-( '( -",- F#,L
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'$
B- Alkali acetate, e.g. sodium acetate as KCN using M.O. HCl
CH3COONa + H2O CH3COOH + NaOH
NaOH + HCl NaCl + H2O
CH3COONa + HCl CH3COOH + NaCl
C- Borax:
1- when dissolved in water hydrolysis:
Na2B4O7+ 7 H2O 4H3BO3 + 2NaOH # HCl
Boric acid is a very weak acid, the producedNaOHcan be directly titrated with HCl using M.O.pH as the end point is acidic due to presence of boric acid (5)
Na2B4O7 + 7H2O + 2HCl 4H3BO3 + 2 NaCl + 2 H2O
2- The neutralized solution can be used for the determination ofboric acid after the addition of
an equal amount of glycerol and titrated with NaOH using ph.ph. sodium borate.(salt of weakacid and strong base).
4H3BO3+ 4NaOH 4 NaBO2 + 8H2O
The volume of st. alkali = 2 volume of st. acid of the same normality.
` +1?2,-1*#L
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'%
`' +1?2,-1*#L
Sodium carbonate hydrolyses in water
Na2CO3+ 2 H2O 2 NaOH + H2CO3
Na2CO3:HCl
Na2CO3 + HCl NaHCO3 + NaCl { ph.ph.} pH 8.3
NaHCO3+ HCl H2CO3+ NaCl {M.O.} pH 3.8
Na2CO3 can be determined by titration against HCl by 2 methods:
a- Using M.O. indicator total carbonateb- Using ph.ph. Indicator CO3
- - and as half neutralization step
Na2CO3 + 2 HCl 2 NaCl + CO2 + H2O .(1)
Na2CO3 + CO2 + H2O 2 NaHCO3 .(2)
(1) + (2)
c?#+1/*(,- )",/&4 2# *1A#- *, A##C %;=(-)(4# *"# ),&-> [V L
,@ +**4'.1 G@ V'1 )'47-'*. */ -"# -'-$,-#) (*4.0
+@ 3*.-'.7*7( (-'$$'.1 -'44 .#7-$,4 -* G'+,$G*.,-# (-#; :;"0;"08
)@ )';;'.1 -"# .*MM4# */ -"# G7$#--# 7.)#$ -"# (7$/,+# */ -"# (*47-'*.0
The first halfneutralization step is supposed to take place in two separate steps:
2 Na2CO3 + 2HCl 2 NaCl + 2 NaHCO3
N' U(O*/?#) ,3 %1?2,-1*#) 1-4 [(+1?2,-1*#)L'D@ 6"# -*-,4 :3?W
A@,.)
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: W W 8 K 2 1
A@ 6"# 3?WA@'( )#-#$C'.#) GK ('C'4,$ -'-$,-'*. G7- 7('.1 ;"0;"0
S0?0 $#,)'.1 J 6*-,4 3?WA@
,.)