Theories of acid and base

Describe in this slide the four theories of acid and base.1) Traditional theory 2) arrhenius theory 3) bronsted and lowry theory 4) lewis theory. also explained neutalisation reaction and amphoteric reactions.

1. THEORIES OF ACID’S
AND BASE’S…
Ms. GopaleK.S.
B.Pharm, MBA.

2. Theories of acid and base.
▪Mainly there are four theories of acid and
base-
1.Traditional Theory
2.Arrhenius Theory
3.Bronstedand Lowry Theory
4.Lewis Theory

3. Traditional theory
▪Acid : Are the substance-
▪Which converts BLUE litmus paper to RED.
▪Having the PH < 7
▪Sour taste.
▪React with bases to form salt and water.
▪Eg. Hydrochloric Acid (HCl)

4. Traditional theory
▪BASE: Are the substance -
▪Which converts RED litmus paper to BLUE.
▪Having the PH >7
▪Bitter taste.
▪React with acids to form salt and water.
▪Eg. Sodium Hydroxide (NaOH)

5. Arrhenius theory
▪In 1884 of SvanteArrhenius proposed a
theory,
It is also called as,
a)Arrhenius theory of ionization.
b)Electron dissociation theory.
•This theory defines acids and bases according
to their formation of ions when dissolved in
water.

6. Arrhenius theory
▪ACID’S :
“ An acid is a substance that can release
hydrogen ion (H+) when dissolved in water.”
(OR)
“A substance which when dissolved in water
gives hydrogen ions (H+) is known as acid.”
Eg. Hydrochloric Acid.
HCl H+ + Cl

7. Arrhenius theory
▪BASE’s :
“ A base is substance that can release a
hydroxyl ion (OH-) when dissolved in water.”
(OR)
“ A substance which when dissolved in
water gives hydroxyl ion is known as Acid.”
Eg. Sodium Hydroxide.
NaOH Na++ OH-

8. Neutralization Reaction
Acid react with Base
forms Salt and Water
Eg. Hydrochloric Acid React with Sodium
Hydroxide Sodium chloride (salt) &
water.
NaOH+ HCl NaCl+ H2O
(Base) (Acid) (Salt) (Water)

9. Neutralization
▪According to Arrhenius theory,
“ Neutralization is the process in which
hydrogen ion and hydroxyl ion combine to
form unionized molecule or water.”
NaOH+ HCl NaCl+ H2O
1. HCl H+ + Cl-
2.NaOH Na+ +OH-

10. LIMITATION’S
▪Water is essential.
▪Not explain acidity or basisityof non-aqueous
solvent. Eg: Benzene.
▪Basisityof Ammonia (no OH-ions) is not
explained.
▪Acidity of BF3, AlCl3 (no H+ ions ) is not
explained.
▪Acidity of oxides of P block element (CO2) is
not explained.

11. LIMITATION’S
▪Basisityof oxides of S block element (Na2O)
is not explained.
▪Neutralization without absence of solvent is
not explained.

12. BRONSTED -LOWRY theory
▪In 1923 , Johannes Bronsted( A danishchemist) and
Thomas Lowry (an englishchemist) proposed new
definitions of acids and bases.

13. BRONSTED -LOWRY theory
▪Bronstedand lowryhad worked independently of
each other but they both arrived at the same
definitions:
▪An acid is a substance that donates protons
(Hydrogen ions).
▪A base is a substance that accepts protons.

14. ACID = PROTON DONOR

15. ACID = PROTON DONOR
▪The HCldonates a proton and so is an acid.
▪The H2O, in this case accepts a proton(H+)
and so it is a base.

16. BASE = PROTON ACCEPTOR
▪The NH3 accepts a proton and so it is a base.
▪The H2O, in this case donates a proton and so
it is an acid.

17. amphoteric
▪As can be seen from the previous two examples,
water is capable of acting as both acid and base.
▪Any substance that can act as both acid and base is
said to be “amphoteric”.

18. Acid-base reaction
▪HCl+ NH3 Cl+ NH4

19. NEUTRALISATION
▪The reaction between an acid and a base to
produce a salt and water.
▪A salt is formed when the hydrogen of an acid
is replaced by a metal. (or ammonium ion)

20. NEUTRALISATION

21. Lewis theory
▪Gilbert Lewis Focused on the donation or
acceptance of a pair of electrons during a
reaction.
▪Lewis Acid –Electron pair acceptor.
▪Lewis Base -Electron pair donor.
▪What happens When an acid dissolves in water ?
▪Water is acts as a base and abstracts a proton
(H+) from the acid.

22. Lewis theory
▪As result the conjugate base (Cl-) of the acid
and a hydroniumion (H3O+) are formed.

23. Lewis acid-base theory
▪LEWIS ACID = A substance that can accepts
an electron pair.
▪LEWIS BASE = A substance that donates an
electron pair.
▪Formation of hydroniumion is also an
excellent example.

24. Lewis acid-base theory
▪Electron pair of the new O-H bond originates
on the lewisbase.

25. Lewis acid-base theory