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

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Bronsted-Lowry; Arrhenius - Acids and Bases; Lewis Theory of Acids and Bases | Basic Chemistry

Learning Outcomes

After studying this lesson, you shall be able to:

  • Bronsted-Lowry definition

  • Arrhenius concept of acids and bases

  • Lewis theory of acids and bases

Bronsted-Lowry Definition

  • The Bronsted-Lowry definition of acids is that acids are compounds that give off H+ ions when they react with another compound.

  • Likewise, this definition says that bases are compounds that accept H+ ions from other compounds.

  • Furthermore, it also brings a new concept of conjugate acids and conjugate bases.

  • Since an acid after donating its proton is technically a base according to this definition and is referred to as a conjugate acid.

  • 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.

Brnsted-Lowry

Brnsted-Lowry

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Arrhenius Concept of Acids and Bases

  • The Arrhenius definition of acids says that they are compounds that give off H+ ions in water and that bases are compounds that give off OH- ions in water.

  • Thus, according to this theory only protic acids are allowed and only hydroxide bases are allowed to be classified as an acid or a base.

Arrhenius

Arrhenius

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Lewis Theory of Acids and Bases

  • Acids are electron pair acceptors while bases are electron pair donors.

  • Thus, electron deficient species like BF3 are Lewis acids while electron rich species such as tertiary amines are Lewis bases.

  • Lewis acids may combine with Lewis bases to generate a salt.

Lewis theory

Lewis Theory

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Lewis Acid-Base Reaction

  • Acid strength is commonly measured by two methods.

  • 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.

  • Thus, solutions that have a low pH have a high hydronium ion concentration and can be said to be more acidic.

  • 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.

  • 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