Lesson Notes By Weeks and Term v4 - SHS 2
EQUILIBRIA
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EQUILIBRIA
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Subject: Chemistry
Class: SHS 2
Term: 1st Term
Week: 20
Grade code: 2.1.2.LI.3
Strand code: 1
Sub-strand code: 2
Content standard code: 2.1.2.CS.2
Indicator code: 2.1.2.LI.3
Theme: PHYSICAL CHEMISTRY
Subtheme: EQUILIBRIA
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Welcome, future scientists and engineers! Today, we delve deeper into the world of acids and bases. We all know some acids and bases from our daily lives in Ghana. The sour taste of an unripe mango or lime is due to acids, while the slippery feel of soap or the relief from "Alka Seltzer" after a heavy meal comes from bases. But are all acids and bases the same? Why is the acid in your stomach (hydrochloric acid) very dangerous outside the body, while the acid in vinegar (ethanoic acid) is safe to put on your food? The answer lies in their strength. This lesson will help you understand the fundamental difference between 'strong' and 'weak' acids and bases.
2.1 The Core Concept: Extent of Dissociation The "strength" of an acid or base is NOT about how corrosive it is or how concentrated it is. In chemistry, strength refers to how well an acid or base dissociates (breaks apart into ions) when dissolved in water.
Dissociation is the process where a compound separates into its constituent ions in a solution.
a) Strong Acids and Strong Bases: Complete Dissociation A strong acid is an acid that dissociates *completely* or *almost completely* in an aqueous solution. This means that nearly every single molecule of the acid breaks apart to release its hydrogen ion (H⁺). We represent this with a one-way arrow (→). Example (Strong Acid): Hydrochloric acid (HCl) `HCl(aq) → H⁺(aq) + Cl⁻(aq)` *In a beaker of HCl solution, you will find almost exclusively H⁺ ions and Cl⁻ ions, with very few undissociated HCl molecules.*
A strong base is a base that dissociates *completely* in an aqueous solution to release hydroxide ions (OH⁻). Example (Strong Base): Sodium hydroxide (NaOH), also known as caustic soda. `NaOH(aq) → Na⁺(aq) + OH⁻(aq)` *In a solution of NaOH, you find almost exclusively Na⁺ ions and OH⁻ ions.*