explaining B-L theory of acids and bases

1. ACID &BASE
THEORIES
Lesson
1:Bronsted/Lowry
Theory of Acids and
Bases

2. OBJECTIVES
Define a Brønsted–Lowry acid as a proton/H+ donor and a Brønsted–Lowry
base is a proton/H+ acceptor.
State that an amphiprotic species can act as both Brønsted–Lowry acids and
bases.
Distinguish between a pair of species differing by a single proton as a
conjugate acid-base pair.

3. BRONSTED/LOWRY THEORY OF
ACIDS AND BASES
Danish chemist Bronsted + English chemist Lowry independently
proposed new definitions for an acid and a base
These simply state that:
Acid is hydrogen-ion donor (H+ or proton)
Base is hydrogen-ion acceptor.
Acids and bases always come in pairs.

4. BRØNSTED-LOWRY
EX:-
HCl When it dissolves in water, it gives it’s proton to
water.
HCl(g) + H2O(l) ↔ H3O+
(aq) + Cl-
(aq)
to understand this reaction watch the hydrogen atom of
HCl.

5. CONSIDER THIS
When hydrogen chloride is added to water the following
reaction occurs
HCl + H2O H3O+ + Cl-
Because this
donates a
proton it is
a B/L acid
Because this
accepts a
proton it is
a B/L base

6. CONSIDER THIS
When ammonia gas dissolves in water the following
reaction occurs
NH3 + H2O NH4
+ +
OH-
Accept
s a
proton
B/L
base
Donate
s a
proton
B/L
acid

7. IMPORTANT NOTE
Water can act as either an acid or a base
for this reason is known as Amphoteric or
Amphiprotic

8. IDENTIFY THE B/L ACID IN THE
FOLLOWING EQUATION
In the following reaction between Hydrogen chloride and
Ammonia
HCl + NH3 NH4
+ + Cl-

9. THE BRØNSTED-LOWRY
MODEL

10. NOTE
An acid will only donate a proton when there is
something there to accept it
A base will only accept a proton if there is something
there to donate it

11. THE BRØNSTED-
LOWRY MODEL
CONJUGATE ACID-BASE PAIR
 When an acid donates its proton, the remaining part of the acid is called the
conjugate base of that acid.

12. THE BRØNSTED-
LOWRY MODEL
CONJUGATE ACID-
BASE PAIR
 Also, when a base accepts a proton, the remaining part of the base is called the
conjugate acid of that base.

13. THE BRØNSTED-LOWRY
MODEL CONJUGATE ACID-
BASE PAIR
Hence,
together the acid and its conjugate base are known as an
conjugate acid-base pair.
The same thing apply on a base and its conjugate acid.

14. IDENTIFY B/L ACID-BASE
PAIRS IN THE FOLLOWING
EQUATIONS
CH3COOH + H2O CH3COO- + H3O+
CH3COO- + H3O+ CH3COOH +
H2O

15. DETERMINE THE ACID, BASE,
CONJUGATE ACID AND CONJUGATE
BASE!
1). 𝐻𝐶𝑙 𝑎𝑞 + 𝑁𝑎𝑂𝐻 𝑎𝑞 → 𝑁𝑎𝐶𝑙 𝑎𝑞 + 𝐻2 𝑂 𝑎𝑞
2). 𝐻2 𝑆𝑂4 + 𝐻2 𝑂 → 𝐻3 𝑂+ + 𝐻𝑆𝑂−
4

16. THE BRØNSTED-
LOWRY MODEL
SUMMARY
1) An acid donates a proton and becomes a
conjugate base.
2) A base accepts a proton and becomes a
conjugate acid.
3) Ampholytes are substances that can behave
either as an acid or a base