Basic Chemistry: Bronsted-Lowry Definition and Lewis Theory of Acids and Bases

Learning Outcomes

After studying this lesson, you shall be able to:

1. Bronsted-Lowry definition
2. Arrhenius concept of acids and bases
3. Lewis theory of acids and bases

Bronsted-Lowry Definition

1. The Bronsted-Lowry definition of acids is that acids are compounds that give off H + ions when they react with another compound.
2. Likewise, this definition says that bases are compounds that accept H + ions from other compounds.
3. Furthermore, it also brings a new concept of conjugate acids and conjugate bases.
4. Since an acid after donating its proton is technically a base according to this definition and is referred to as a conjugate acid.
5. So, every acid has its conjugate base and vice versa. Also, the stronger is an acid, the weaker is its conjugate base and vice versa.

Arrhenius Concept of Acids and Bases

1. The Arrhenius definition of acids says that they are compounds that give off H + ions in water and that bases arecompounds that give off OH- ions in water.
2. Thus, according to this theory only protic acids are allowed and only hydroxide bases are allowed to be classified as anacid or a base.

Lewis Theory of Acids and Bases

1. Acids are electron pair acceptors while bases are electron pair donors.
2. Thus, electron deficient species like BF3 are Lewis acids while electron rich species such as tertiary amines are Lewis bases.
3. Lewis acids may combine with Lewis bases to generate a salt.

Lewis Acid-Base Reaction

1. Acid strength is commonly measured by two methods.
2. One measurement, based on the Arrhenius definition of acidity, is pH, which is a measurement of the hydronium ion concentration in a solution, as expressed on a negative logarithmic scale.
3. Thus, solutions that have a low pH have a high hydronium ion concentration and can be said to be more acidic.
4. The other measurement, based on the Bronsted-Lowry definition, is the acid dissociation constant (Ka) , which measure the relative ability of a substance to act as an acid.
5. That is, substances with a higher Ka are more likely to donate hydrogen ions in chemical reactions than those with lower Ka values.

MCQs

1. Solutions that have a low pH have a high

1. Hydronium ion

2. Hydroxide ion

3. Both

4. none

Answer: Hydronium ion

2. Acid after donating its proton is referred as

1. conjugate acid

2. conjugate base

3. Base

4. none

Answer: A. conjugate acid

#Bronsted-Lowry definition

#Arrhenius concept of acids and bases

#Lewis theory of acids and bases