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: 3
Grade code: 1.1.2.LI.2
Strand code: 1
Sub-strand code: 2
Content standard code: 1.1.2.CS.1
Indicator code: 1.1.2.LI.2
Theme: PHYSICAL CHEMISTRY
Subtheme: EQUILIBRIA
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This lesson explores the concept of solubility, which is a specific type of equilibrium. We encounter solubility every day – from dissolving sugar in our morning *koko* or tea, to large-scale industrial processes like salt production at Ada Foah and Keta. Understanding how much of a substance can dissolve in a solvent, and how factors like temperature affect this, is fundamental to chemistry. A saturated solution is a perfect example of a dynamic equilibrium, where the rate of dissolving is equal to the rate of crystallization.
2.1. Fundamental Definitions Solute: The substance that dissolves in a solvent (e.g., salt, sugar). Solvent: The substance in which the solute dissolves (e.g., water, ethanol). Water is often called the "universal solvent". Solution: A homogeneous mixture formed when a solute dissolves in a solvent. 2.2. Types of Solutions Unsaturated Solution: A solution that contains less solute than the maximum amount it can dissolve at a given temperature. If you add more solute, it will dissolve. Saturated Solution: A solution that contains the maximum amount of solute it can dissolve at a given temperature in the presence of undissolved solute. In a saturated solution, a dynamic equilibrium exists between the dissolved solute and the undissolved solid solute. The Equilibrium Connection: `Solute(solid) ⇌ Solute(dissolved)` This means the rate at which the solid solute dissolves is exactly equal to the rate at which the dissolved solute crystallises back into a solid. The overall concentration of the solution remains constant. Supersaturated Solution: An unstable solution that contains more dissolved solute than a saturated solution at the same temperature. This is usually prepared by dissolving a solute in a hot solvent and then cooling it carefully without disturbance. If a single seed crystal is added, the excess solute will rapidly crystallise out. 2.3. What is Solubility? Solubility is defined as the maximum mass (in grams) of a solute that will dissolve in 100g of a solvent at a specific temperature to form a saturated solution. Units: The standard unit for solubility in this context is g/100g of solvent. For example, if the solubility of Potassium Nitrate (KNO₃) in water at 20°C is 31.6 g/100g H₂O, it means a maximum of 31.6g of KNO₃ can dissolve in 100g of water at that temperature. Solubility can also be expressed in mol/dm³, which is also known as molar solubility. 2.4. Calculating Solubility
Solubility can be calculated using a simple ratio and proportion method based on experimental data.
Formula: `Solubility = (Mass of solute / Mass of solvent) x 100`