The definition of Acids and Bases based on Bronsted-Lowery Model. It describes the fundamental properties of both the acids and the bases.

1. PHYSICAL SCIENCES
GRADE 11
BRONSTED-
LOWRY
DEFINITION
OF ACIDS
AND BASES
Author: M.C.B MNCUBE

2. OBJECTIVES:
a) Define an acid and the base according
to Bronsted-Lowry definition.
b) Explain using the chemical equation
how a proton transfer occur.
c) Identify an conjugate acid-base pairs.

3. Bronsted-lowry definition of
acids and bases
Bronsted and Lowry explain
acid and base based on their
actions in a chemical reaction.
Their theory is the
development of Arrhenius
theory or simply an expansion
of Arrhenius acid definition.

4. The Brønsted-Lowry Model
Definition:
The Brønsted-Lowry Model of
acids and bases states that an
acid is a hydrogen ion donor,
and a base is a hydrogen ion
acceptor.

5. The Brønsted-Lowry Model
Example on proton transfer
Acids are proton donors, hence acids
release protons in the presence of bases
Bases are proton accepters, hence bases
take up protons in the presence of acids
𝐻𝐶𝑙 𝑔 → 𝐻+
𝑎𝑞 + 𝐶𝑙−
𝑎𝑞 𝑁𝐻3 𝑔 + 𝐻+ →. 𝑁𝐻4
+
.

6. The Brønsted-Lowry Model
As the results Brønsted and Lowry rectify Arrhenius Model Limitations that:
 Acid-base reaction only occurs in aqueous medium.
 The bases are substances that only produce hydroxide ions 𝑂𝐻−
.
A Base without Hydroxide ions

7. The Brønsted-Lowry Model
examples:
– NH3(aq) + H2O(l) ↔ NH4
+(aq) + OH–(aq)
– NH3 = base, H2O(l) = acid, NH4
+ = conjugate
acid, OH– = conjugate base
NB: ‘’The examples above implies that water can act both as an acid and a base
depending on whether is acid or base among the reactants’’

8. The Brønsted-Lowry Model
water among reactants:
 When an acid is dissolved in water, the reaction involves the transfer of a proton
from the acid to the water.
 Also, when a base is dissolved in water, the reaction involves proton transfer
from water to the base.
NB: As a proton is small and unstable, and when present in water, the
water and the proton react to form a hydronium or oxonium ion,
represented as

9. 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.

10. 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.

11. 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.

12. HENCE, a reaction must have
an acid, a base, a conjugate
acid and a conjugate base

13. 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

14. The Brønsted-Lowry Model
Exercises
ITS TIME TO DO AN EXPERIMENT REGARDING YOUR
PROGRESS MY FOLLOW COLLEAGUES!!!

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
3). The hydrogen sulfite ion, HSO3-, is amphoteric. Write
its equations with water, acting as both acid and base.

16. The Brønsted-Lowry Model
REFERENCES
Bookstaver, JD. chapter 16 Acids and Bases. Available from Slideshare at
https://www.slideshare.net/jhamze/ap-chemistry-chapter-16-
outline?qid=2304d113-e70f-4cc2-bb2f-1821a377f48d&v=&b=&from_search=42
(Accessed 18 September 2017).
Joshi, M. (2010), Acids, Bases and Salt. A Guide for GCSE Students. Available from
Slideshare at https://www.slideshare.net/maitreyeej3/acids-bases-and-salts-igcse-
chemistry?qid=225b168e-a754-420f-8423-7b02ee3599a5&v=&b=&from_search=7
(Accessed 18 September 2017).

17. The Brønsted-Lowry Model
REFERENCES
Mani, PK. Acid-Base Titration. Available from Slideshare at
https://www.slideshare.net/pabitramani/titrimetrey-as-analytical-
tool?qid=2304d113-e70f-4cc2-bb2f-1821a377f48d&v=&b=&from_search=4
(Accessed 18 September 2017).
Muñoa, R. Acids and Bases: Theory. Available from Slideshare at
https://www.slideshare.net/rafamunoa/theories-5865342?qid=2304d113-e70f-
4cc2-bb2f-1821a377f48d&v=&b=&from_search=5 (Accessed 18 September 2017).

18. The Brønsted-Lowry Model
REFERENCES
Vania and michelle. (2011). Brønsted-Lowry Acids and Bases. Available from
Slideshare at https://www.slideshare.net/vanialundina/acid-base-
7323554?qid=2304d113-e70f-4cc2-bb2f-1821a377f48d&v=&b=&from_search=17
(Accessed 18 September 2017).