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1. DETERMINATION OF
ACIDITY AND BASICITY
Kurdistan Region –Iraq
Ministry of Higher Education andScientific
Research
DEPARTMENT OF RADIOLOGICAL
IMAGING TECHNOLOGIES
[email protected]

2. contents
•Background
•Acidity & Basic or Alkali
•Acid Base Chemistry
•Arrhenius Acids and Bases
Reactions of Brønsted-Lowry Acids and Bases
* Lewis Acids and Bases
Acid Strength and pK
a
FactorsthatDetermineAcidStrength
Inductive effects
Resonance effects

3. •Throughouthistory,wehavecometogivebetter
andbetterdefinitionsofthingsasweunderstand
thembetter.Acidbasetheoryareoneofthethings
thathaveundergonethiskindofprogress.
•Inthebeginning,wedescribedacidsas
substanceswithsour,corrosiveproperties,and
basesaskindofsoapy..
Background

5. Litmus paper

6. Basic or Alkali:-
Theword(alkali)issynonymouswithbase.Itisof
Arabicorigin,buttherootwordcomesfromthesame
Latinkalium(potash)thatistheoriginofthesymbol
forpotassium.Generallybasiccompounds
characterizedby:
1-Abittertaste.
2-A soapy feeling when applied to the skin,dissolve oils and
grease
3-Ability to restore the original (bluecolor of litmus
that has been turned red )by acids.
4-Ability to react with acids to form salts.

7. Acid-Base Chemistry
•Acids/Bases Classified in a Number of Ways
Arrhenius(Hydrogen and Hydroxide Ions)
Brønsted—Lowry(H+ Donors and
Acceptors)
Lewis(Lone Pair( e )Donors and Acceptors))

8. Arrhenius Acids and Bases
TheArrheniusdefinitionofacidsandbasesisoneof
theoldest.AnArrheniusacidisasubstancethatwhen
addedtowaterincreasestheconcentrationofH
+
ions
present.
AnArrheniusbaseisasubstancethatwhenaddedto
waterincreasestheconcentrationof
-
OHionspresent.

9. HCl is an example of an Arrhenius acid
NaOH is an example of an Arrhenius base.

10. (Brønsted—Lowry) Acids and BasesOH
H
H Br+
HOH
H
+Br
Base Acid Conjugate AcidC. Base
•A Brønsted-Lowry: acid is a proton donor.
•A Brønsted-Lowry : base is a proton acceptor.
•H
+
= proton

11. 11
ReactionsofBrønsted-LowryAcidsandBases
•ABrønsted-Lowryacidbasereactionresultsinthetransferof
aprotonfromanacidtoabase.
•Inanacid-basereaction,onebondisbroken,andanotheroneis
formed.
•TheelectronpairofthebaseB:formsanewbondtotheproton
oftheacid.
•TheacidH—Alosesaproton,leavingtheelectronpairinthe
H—AbondonA.OH
H
H Br+
HOH
H
+Br
..

13. Common Strong (Inorganic) Acids
•HCl (Hydro chloric)
•HBr (Hydro bromic)
•HI(Hydro iodic)
•HNO
3(Nitric)
•HClO
4(Perchloric)
•H
2SO
4(Sulfuric)
All Classified as Brønsted Acids (H
+
Available to Donate)

14. Lewis Acids and Bases
•Lewis Acid: Lone Pair e Acceptor
•Lewis Base: Lone Pair e Donor
•Reaction MechanismIH NH
3
+ NH
4 + I
..

15. Lewis Acids & Bases
A Lewis acid and base can interact by sharing an
electron pair.
Formation of hydronium ion is an excellent
example.H
H
H
BASEACID
O—H
••
•
•
••
O—H
H
+
+

16. 16
AcidStrengthandpK
a
•Acidstrengthisthetendencyofanacidtodonatea
proton.
•Themorereadilyacompounddonatesaproton,the
strongeranaciditis.
•Acidityismeasuredbyanequilibriumconstant.
•WhenaBrønsted-LowryacidH—Aisdissolvedin
water,anacid-basereactionoccurs,andan
equilibriumconstantcanbewrittenforthereaction.

18. 18
BecausetheconcentrationofthesolventH
2Ois
essentiallyconstant,theequationcanberearrangedand
anewequilibriumconstant,calledtheacidityconstant,
K
a,canbedefined.
Itisgenerallymoreconvenientwhendescribingacid
strengthtouse“pK
a”valuesthanK
avalues.
Acid ionization constant

19. 19
FactorsthatDetermineAcidStrength
•AnythingthatstabilizesaconjugatebaseA:¯
makesthestartingacidH-Amoreacidic.
The degree of dissociation of an acid depends on the
following two factors. In generalweaker the strength
of H-A bond, stronger is the acid. Similarly, greater the
polarity of H-A bond, stronger is the acid

20. •FourfactorsaffecttheacidityofH-A
1-Elementeffects
The acidity of H –A increases both left-to-right across
a row and down a column of the periodic table.
2-Inductiveeffects
TheacidityofH–Aincreaseswiththepresence
ofelectron-withdrawinggroupsinA.

21. 3-Resonanceeffects
TheacidityofH–Aincreaseswhenthe
conjugatebaseA:–isresonancestabilized.
4-Hybridizationeffects
TheacidityofH–Aincreasesasthe
percentS-characteroftheA:–increases.