Bronsted-Lowry Concept: Understanding Acids and Bases as Proton Donors and Acceptors, Lecture notes of Chemistry

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B.Sc. (Honours) Part-I

Paper-IA

Topic: Bronsted-Lowry Concept

UG

Subject-Chemistry

Dr. Laxman Singh

Asst. Professor

Department of Chemistry

R.R.S. College (PPU)

(Mokama, Patna)

Acid & Base

Acids and bases can be classified on the basis of their properties.

Acids :

(i) They are sour in taste.

(ii) They react with some metals and produce

hydrogen

(iii)They react with carbonate (Na 2 CO 3 ) and bicarbonate

(NaHCO 3 ) and produce CO 2 :

(iv) Solution of acids in water conducts electricity.

(v) They change the colour of litmus from blue to red.

Base :

(i) They have bitter taste.

(ii) They change colour of litmus from red to blue.

(iii) They are slippery in nature.

(iv) Aqueous base solution conducts electricity.

Bases :

(i) Molecular bases

(ii) Anion bases (OH–, S^2 – , CO 32 – , Cl–, Br–, NO 3 – )

(iii) Cationic bases

Conjugate acids and bases:

Bronsted-Lowry also gave the concept of conjugate acid base pair. Conjugate base is a species that remains when one proton has been removed from the acid.

Conjugate acid results from the addition of proton to a base

An acid base pair which is different by a proton is called conjugate acid base pair.

The sum of these two reactions is

Therefore, any acid-base reaction involves two acids and two bases. These acids and bases are called conjugate pairs.

4

Relative strength of conjugate acid – base pairs

Strong acids

Acid Conjugate base HClO 4 ClO – HI I– HBr Br– HCl Cl– H 2 SO 4 HSO 4 – HNO 3 NO 3 –

Increasing base Strength

Weak acids

H 3 O+^ H 2 O

HSO 4 –^ SO 42 –

HF F–

HNO 2 NO 2 –

HCOOH HCOO–

CH 3 COOH HCOO

NH 4 +^ NH 3

HCN CN–