solubility 3

 Here’s a student-friendly explanation of Solubility, combining your detailed notes with scientific terms, simplified language, and examples, ideal for presentation or class notes:

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🧪 Solubility – Class 12 Chemistry

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🔬 Scientific Definition:

Solubility is the maximum amount of solute that can be dissolved in a specified amount of solvent at a given temperature and pressure to form a saturated solution.

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📌 Key Points to Remember:

• Solubility is measured in grams per 100g of solvent or in mole fraction/molarity.

• It depends on:

  • Nature of solute and solvent

  • Temperature

  • Pressure (for gases only)

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🧠 Why “Like Dissolves Like”?

• Polar solutes dissolve in polar solvents (e.g., NaCl in water).

• Non-polar solutes dissolve in non-polar solvents (e.g., naphthalene in benzene).

❌ Sugar does not dissolve in benzene
✅ Sugar dissolves well in water

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🔄 Dissolution and Crystallisation – Dynamic Equilibrium

When a solute is added to solvent:

• Dissolution happens → solute dissolves

• Crystallisation also starts → dissolved solute particles come out

At some point, both processes become equal:

Dissolution = Crystallisation → Dynamic Equilibrium

At this stage, the solution becomes saturated, and the concentration becomes constant.
✅ Solubility = Concentration at saturation point

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🔥 Effect of Temperature on Solubility

For solids in liquids:

• If dissolution is endothermic (∆H > 0):
  → Solubility increases with temperature (e.g., KNO₃ in water)

• If exothermic (∆H < 0):
  → Solubility decreases with temperature

For gases in liquids:

• Solubility always decreases with increase in temperature
  (Gas escapes more at higher temperature)

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🧯 Effect of Pressure (Only for Gases)

For gases in liquids:

• Higher pressure = higher solubility
  (More gas particles get pushed into the solution)

This is explained by Henry’s Law:

p = KH × x
Where,
p = partial pressure of gas
x = mole fraction of gas in solution
KH = Henry’s law constant

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🧪 Henry’s Law Applications

1. Soft drinks: CO₂ is filled under high pressure to increase solubility.

2. Scuba diving: Divers use oxygen–helium mixtures to avoid bends caused by nitrogen bubbles.

3. High altitudes: Low oxygen pressure causes low oxygen solubility in blood, leading to anoxia.

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🧊 Important Table: KH Values (Gas Solubility)

Gas	Temp (K)	KH (kbar)	Solubility
O₂	293	34.86	Moderate
CO₂	298	1.67	Very High
He	293	144.97	Very Low

Higher KH = Lower Solubility

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✅ In Summary:

• Solubility is a measure of how much solute dissolves in a solvent.

• Saturated solution = no more solute dissolves.

• For solids: temperature matters, pressure doesn’t.

• For gases: both temperature and pressure matter.

• Henry’s Law shows the direct relationship between gas pressure and solubility.

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