1. Acids and Bases

2. Lactic acid
Citric acid
Common household
acids
Stearic acid
Ethanoic acid
Acetylsailicylic
Acid

3. Common laboratory acids




Hydrochloric acid
Nitric acid
Sulfuric acid
Phosphoric acid
-
HCl
HNO3
H2SO4
H3PO4

4. Arrhenius theory of acid



Arrhenius was a Sweedish
chemist
Put forward a theory of
acids in the 1880’s
Stated that:
An acid is a substance that dissociates
in water to form H+ ions.

5. Arrhenius theory of acid
For example: when HCl is added to
water:
HCl
H+ + ClIn general:
HA
H+
+
A-

6. Acids



HCl and HNO3 are monobasic acids as they donate
one H+ ion.
HNO3
H+
+ NO3-
H2SO4 is a dibasic acid as it donates two H+ ions.
H2SO4
2H+
+ SO42H3PO4 is a tribasic acid as it donates three H+ ions.
H3PO4
3H+
+ PO43-

7. 
A strong acid is one which dissociates fully
in water
Example: HCl, H2SO4, HNO3
HCl + H2O
H3O+ + Cl-

A weak acid is one which does not fully
dissociate in water
Example: CH3COOH (ethanoic acid)
CH3COOH + H2O
H3O+ + CH3COO-

8. Magnesium
hydroxide
Ammonia
Common household
bases
Sodium
hydroxide
Calcium hydroxide
Sodium hydrogen carbonate

9. Common laboratory bases




Sodium hydroxide
Calcium hydroxide
Ammonia
Sodium carbonate
-
NaOH
Ca(OH)2
NH3
Na2CO3

10. Arrhenius theory of bases



Arrhenius defined a base as:
A substance that dissociates in water to
produce OH- ions.
For example: when NaOH is added to water:
NaOH
Na+ + OHIn general:
XOH
X+
+
OH-

11. 
A strong base is one which dissociates
fully in water
Example: NaOH

A weak base is one which does not
fully dissociate in water
Example: Mg(OH)2

12. Arrhenius theory

Combining:
HA
XOH
we get:
HA + XOH
acid + base
H+
X+
+
+
AOH-
AX + H2O
salt + water

13. Limitations of Arrhenius theory
1.
2.
3.
The acids and bases must be in aqueous
solutions (i.e. water). This prevents the use of
other solvents benzene.
Not all acid – base reactions are in solution, e.g.
ammonia gas and hydrogen chloride gas produce
ammonium chloride.
According to Arrhenius, the salt produced should
not be acidic or basic. This is not always the
case, for example in the above reaction
ammonium chloride is slightly acidic

14. Hydronium Ion





Arrhenius thought that an acid gives off H+ ions
in solution.
H+ ions are protons and can not exist
independently.
When the acid dissociates, the H+ ions react
with water molecules:
H + + H 2O
H 3O+
The H3O+ ion is called the hydronium ion.
This is another limitation of the Arrhenius
theory.

15. Brønsted-Lowry Theory

In 1923, Johannes Brønsted (a Danish
chemist) and Thomas Lowry (an English
chemist) proposed new definitions of acids
and bases.
Brønsted
Lowry

16. Brønsted-Lowry Theory

Brønsted and Lowry had 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.

17. Acid = Proton Donor
Donates a Proton
HCl
+
H2O
H3O+
+
Cl-
Accepts a Proton


The HCl donates a proton and so is an acid
The H2O, in this case, accepts a proton and so is a
base
Remember: Proton = H+

18. Likewise:

HNO3
+ H2O
H3O+ +
NO3-
and

H2SO4 + H2O
H3O+ + HSO4-

HSO4- + H2O
H3O+ + SO4-2

19. Base = Proton Acceptor
Accepts a proton
NH3 + H2O
NH4+ + OHDonates a proton


The NH3 accepts a proton and so is a base.
The H2O, in this case, donates a proton and
so is an acid.

20. Amphoteric


As can be seen from the previous two
examples, water is capable of acting
as both and acid and a base.
Any substance that can act as both an
acid and a base is said to be
amphoteric.

21. Acid – Base Reaction
Acid – Donates Protons
HCl
+
NH3
Cl- + NH4+
Base – Accepts Protons

22. 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)

23. Neutralisation
Acid + Base
Salt + Water
HCl + NaOH
NaCl + H2O
but since the acid and base dissociate in water
we can write:
H+ + Cl- + Na+ + OHNa+ + Cl- + H2O
we can cancel the Na+ and Cl- on both sides
leaving:
H+ + OHH2O

24. Everyday Examples of Neutralisation
Indigestion remedies are
bases that neutralise excess
stomach acid
Lime is a base that
neutralises acid in soil
Toothpaste is a base
that neutralises acid in
the mouth

25. Wasp stings are basic
Nettle, bee and ant stings
are acidic
They can be neutralised
with vinegar or lemon
juice
They can be neutralised
with baking soda

26. Conjugate Acid-Base Pairs


Acids and bases exist in pairs called
conjugate acid-base pairs.
Every time an acid donates/loses a
proton, it becomes its conjugate base.
Example:
CH3COOH + H2O
Acid
CH3COO- + H3O+
Conjugate Base

27. Likewise:
 When a base accepts a proton, it
becomes its conjugate acid.
Example:
NH3 + H2O
Base
NH4+ + OH-
Conjugate
Acid

28. Examples:
Conjugate
Acid
H2SO4 + H2O
Base
Base
HSO4- + H3O+
Conjugate
Acid
Conjugate
Acid
NH3
Base
+ H2 S
Base
NH4+ + HS-
Conjugate
Acid