Chemistry - Solutions | Lecture 2
By Abhishek Sengar
Lecture Chapters
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Theory & Quick Notes
1 Solubility & Types of Solutions
Solubility is defined as the maximum amount of solute that can be dissolved in a given amount of solvent at a specific temperature and pressure.
Unsaturated
Contains less solute than the maximum possible amount. You can dissolve more solute into it.
Saturated
Contains the maximum possible dissolved solute. Rate of dissolution = Rate of crystallization.
Supersaturated
Contains more dissolved solute than theoretically possible (metastable state). Tends to crystallize out.
2 Solubility Factors (Solid in Liquid)
The golden rule here is "Like dissolves like". Polar solutes dissolve in polar solvents (like NaCl in water), and non-polar solutes dissolve in non-polar solvents.
Effect of Temperature
- Endothermic Dissolution (ΔH > 0): Solubility increases as temperature increases (e.g., dissolving sugar in water).
- Exothermic Dissolution (ΔH < 0): Solubility decreases as temperature increases.
Effect of Pressure
Pressure has virtually no effect on the solubility of a solid in a liquid because both solids and liquids are highly incompressible.
3 Gas in Liquid & Henry's Law
The dissolution of a gas in a liquid is always an exothermic process (ΔH < 0). Therefore, by Le Chatelier's principle, the solubility of gases in liquids always decreases with an increase in temperature.
Henry's Law
The solubility of a gas in a liquid is directly proportional to the partial pressure of the gas present above the surface of the liquid or solution.
Where p = partial pressure, x (χ) = mole fraction, and KH = Henry's Law Constant.
Important: As KH increases, solubility decreases!
Real-world Applications of Henry's Law:
- Soft Drinks: Sealed under high pressure to increase the solubility of CO₂.
- Scuba Diving (Bends): High underwater pressure causes excess N₂ to dissolve in blood. As divers ascend, N₂ bubbles out, causing painful "bends". Tanks are diluted with Helium (less soluble) to prevent this.
- High Altitudes (Anoxia): Low atmospheric pressure means less O₂ dissolves in the blood, leading to weakness and inability to think clearly, a condition known as anoxia.
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Lecture 2 Checkpoint
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