first & second&third lectures acid base (1&2&3).pdf

8/10/2019 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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#(


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



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#)


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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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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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

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C5 +"1-0#) )&,@&V

Strong base

Weak acid7

9

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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@

,.)

first & second&third lectures acid base (1&2&3).pdf

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