Lesson Notes By Weeks and Term v4 - SHS 3
EQUILIBRIA
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EQUILIBRIA
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Subject: Chemistry
Class: SHS 3
Term: 2nd Term
Week: 13
Grade code: 3.1.2.LI.2
Strand code: 1
Sub-strand code: 2
Content standard code: 3.1.2.CS.1
Indicator code: 3.1.2.LI.2
Theme: PHYSICAL CHEMISTRY
Subtheme: EQUILIBRIA
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This lesson delves into the concept of chemical equilibria as it applies to weak acids and bases. Unlike strong acids and bases which dissociate completely in water, weak ones exist in a state of balance, or equilibrium, where only a small fraction of their molecules break apart (ionize) at any given time. Understanding this partial ionization is fundamental to chemistry. In our daily Ghanaian lives, this concept is everywhere: it explains why the fermented maize dough for *kenkey* or *banku* tastes sour but doesn't burn our tongues like concentrated acid. It's crucial for understanding how our local soils support crops like cocoa and cassava, and how medicines work in our bodies.
Part 1: Strong vs. Weak Acids and Bases - The Concept of Ionization
In chemistry, the "strength" of an acid or base does not refer to its concentration, but to its ability to ionize or dissociate in water. Ionization/Dissociation: The process where a molecule splits into charged particles (ions) when dissolved in a solvent like water.
Strong Acids & Bases: These substances ionize completely (or nearly 100%) in water. We use a single forward arrow `(→)` to show this one-way reaction. Strong Acid Example (HCl): When Hydrochloric acid is added to water, every single HCl molecule splits into H⁺ and Cl⁻ ions. `HCl(aq) → H⁺(aq) + Cl⁻(aq)` Strong Base Example (NaOH): Similarly, every formula unit of Sodium Hydroxide splits into Na⁺ and OH⁻ ions. `NaOH(aq) → Na⁺(aq) + OH⁻(aq)`
Weak Acids & Bases: These substances ionize only partially or incompletely in water. This means at any given moment, most of the molecules remain un-ionized. This creates a reversible reaction, which leads to a state of dynamic equilibrium. We use equilibrium arrows `(⇌)` to represent this. Weak Acid Example (Ethanoic Acid, CH₃COOH): This is the acid in vinegar. When dissolved in water, only a small fraction of the molecules release their proton. `CH₃COOH(aq) ⇌ H⁺(aq) + CH₃COO⁻(aq)` In a solution of vinegar, most of the ethanoic acid exists as intact `CH₃COOH` molecules. Weak Base Example (Ammonia, NH₃): Ammonia accepts a proton from water, but only does so to a small extent. `NH₃(aq) + H₂O(l) ⇌ NH₄⁺(aq) + OH⁻(aq)` Most of the ammonia remains as `NH₃` molecules.