9.3 Strength of Acids and Bases

This topic explains the strength of acids and bases. It describes how the ability to donate or accept protons determines whether an acid or base is strong or weak.

Definition

Strength of Acid: The ability of an acid to donate a proton.

Strength of Base: The ability of a base to accept a proton.

Main Idea

Different Brønsted acids donate protons to different extents. An acid which can donate a proton to a higher degree than another acid is said to be a relatively strong acid. For example, hydrochloric acid is a relatively stronger acid than acetic acid. Also, acetic acid is relatively stronger than water. The ability of an acid to donate a proton is called 'strength of acid' or the 'acid strength' . Similarly, the bases also differ in their ability to accept protons. A base which can accept a proton to a higher degree than another base is a relatively stronger base. Thus ammonia is a relatively stronger base than water because ammonia can accept a proton to a higher degree than water.

Core Concept

• Strong acid: Donates protons to a higher degree.
• Weak acid: Donates protons to a lesser degree.
• Strong base: Accepts protons to a higher degree.
• Weak base: Accepts protons to a lesser degree.
• Relative strength: Compared to other acids or bases.

Detailed Explanation

Strength of Acids

• Different Brønsted acids donate protons to different extents.
• An acid which can donate a proton to a higher degree than another acid is said to be a relatively strong acid.
• Example: Hydrochloric acid (HCl) is a relatively stronger acid than acetic acid (CH₃COOH).
• Also, acetic acid is relatively stronger than water.
• The ability of an acid to donate a proton is called 'strength of acid' or the 'acid strength' .

Strength of Bases

• The bases also differ in their ability to accept protons.
• A base which can accept a proton to a higher degree than another base is a relatively stronger base.
• Example: Ammonia (NH₃) is a relatively stronger base than water (H₂O) because ammonia can accept a proton to a higher degree than water.

Comparison of Acid Strength

Comparison of Base Strength

Intermediate Level

Strength of Acids and Bases

Comparison

• HCl > Acetic acid > Water (acid strength)
• NH₃ > Water (base strength)

Key Point

• Strength is relative.
• Strong acids have weak conjugate bases.
• Strong bases have weak conjugate acids.

Important Points

• 1. Strength of acid: Ability to donate protons.
• 2. Strength of base: Ability to accept protons.
• 3. Strong acid: Donates protons to a higher degree.
• 4. Weak acid: Donates protons to a lesser degree.
• 5. Strong base: Accepts protons to a higher degree.
• 6. Weak base: Accepts protons to a lesser degree.
• 7. Examples: HCl > acetic acid > water (acid); NH₃ > water (base).

Remember

• - Strong acid: Donates protons easily
• - Weak acid: Donates protons with difficulty
• - Strong base: Accepts protons easily
• - Weak base: Accepts protons with difficulty
• - Examples: HCl > acetic acid > water; NH₃ > water

Common Mistakes

• 1. Confusing strength with concentration: Strength is about degree of donation/acceptance; concentration is about amount.
• 2. Thinking all acids are strong: Some are weak (e.g., acetic acid).
• 3. Forgetting that strength is relative: Compared to other acids or bases.
• 4. Mixing up acid and base strength: Acid = donate protons; Base = accept protons.

Quick Revision

• Strength of acid: Ability to donate protons.
• Strength of base: Ability to accept protons.
• Strong acid: Donates protons to a higher degree.
• Weak acid: Donates protons to a lesser degree.
• Strong base: Accepts protons to a higher degree.
• Weak base: Accepts protons to a lesser degree.
• Examples: HCl > acetic acid > water (acid); NH₃ > water (base).

60-Second Revision

• Strong acid: Donates protons easily
• Weak acid: Donates protons with difficulty
• Strong base: Accepts protons easily
• Weak base: Accepts protons with difficulty
• Examples: HCl > acetic acid > water; NH₃ > water

QUALITY VALIDATION

• Topic: 9.3 Strength of Acids and Bases
• Chapter: 9 (Acids-Bases Chemistry)

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• Equations checked: N/A
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