Solubility
Solubility of a substance is its maximum amount that can be dissolved in a specified amount of solvent at a specified temperature. It depends upon the nature of solute and solvent as well as temperature and pressure.
Factors Affecting Solubility
A) Solubility of a solid in a Liquid : Every solid does not dissolve in a given liquid.
Polar solutes [ sodium chloride ( Nacl ), sugar ] dissolve in polar solvents ( water ) but non - polar solutes( naphthalene and anthracene ) dissolve in non - polar solvents (benzene), because intermolecular interactions are similar in the polar solutes to polar solvents and non - polar solutes to non - polar solvents.
Or,Like dissolves like.
Dissolution : When a solid solute is added to the solvent,some solute dissolves and it's concentration increases in solution.This process is known as dissolution.
Example : Sugar dissolving in tea.
Crystallisation: Some solute particles in solution collide with the solid solute particles and get separated out of solution.This process is known as crystallisation.
Example : Salt from seawater
A stage is reached when the two processes ( dissolution and crystallisation) occur at the same rate. or rate of dissolution = rate of crystallisation. Under such conditions, number of solute particles going into solution = number of solute particles separating out and a state of dynamic equilibrium is reached. At this stage the concentration of solute in solution will remain constant the given conditions,i.e temperature and pressure.
Saturated solution : A solution in which no more solute can be dissolved at the same temperature and pressure.
Unsaturated solution : A solution in which more solute can be dissolved at the same temperature.
Supersaturated solution : Solution containing more solute than saturation level (unstable).
Le Chateliers Principle : “System hamesha aise direction me shift hota hai jisse diya gaya change kam ho jaye.”
Effect of Temperature [ In a nearly saturated solution ]
Case 1: Endothermic dissolution (ΔH > 0) [ Heat absorb]
Reaction: Solute + Solvent + Heat ⇌ Solution
Now, Heat badhane par temperature badhega or temperature reactant side me badhega, iska matlab reaction backward side ki or sift ho raha hai. Ab Le Chateliers principle ke anusaar reaction forward direction me shift hoga ( temperature ko balance karne ke liye) to product badhega or dissolution badhega or solubility badhegi.
Temperature ↑ → Solubility ↑
- Heat dene se dissolution (forward) badhta hai.
- Forward rate > backward rate
- Equilibrium right shift hoga
- Solubility should increase with rise in temperature.
Case 2: Exothermic dissolution (ΔH < 0) [ Heat release ]
Reaction: Solute + Solvent ⇌ Solution + Heat
(Yahan heat product side me hai)
Ab heat badhane par temperature badhegi product side me,iska matlab hua jo reaction shift hua forward side ki taraf. Ab Le Chateliers ke anusaar system ko balance karne ke liye reaction shift hoga reverse ( backward) direction ki tarah , iska matlab reactants badhega, jab reactants badhega to product kam banega,or rate of dissolution kam hoga or rate of crystallisation jyada to solubility ghategi.
- Temperature ↑ → Solubility ↓
- Heat dene se crystallization (backward) badhta hai.
- Backward rate > forward rate
- Equilibrium left shift hoga.
- solubility decreased.
Effect of Pressure
Pressure does not have any significant effect ( clearly effect) on solubility of solids in a liquids. It is so because solids and liquids are highly incompressible and practically remain unaffected by changes in pressure.[ Solubility of solids in a liquids me pressure ka koi clearly effect nahi hota because, solid or liquid incompressible hota hai matlab isko dabayaa nahi ja sakta hai. ]
B) Solubility of a gas in a Liquid
Many gases dissolve in water.Oxygen dissolves only to a small extent in water. It is this dissolved oxygen which sustains all aquatic life. On the other hand , hydrogen chloride ( HCl) is highly soluble in water. Solubility of gases in liquids is greatly affected by pressure and temperature. The solubility of gases increase with increase of pressure.
Explanation : Bahut saare gas paani me ghulte hai.
Oxygen paani me bahut kam amount me dissolve hoti hai.
Jo thodi si oxygen paani me ghuli hoti hai, wahi machhli aur paani ke jeev (aquatic life) ko jeene me madad karti hai.
Dusri taraf, Hydrogen Chloride (HCl) paani me bahut zyada amount me dissolve hota hai (highly soluble).
Gas ki solubility (ghulne ki capacity) pressure aur temperature par depend karti hai.
Jab pressure badhta hai, to gas ki solubility bhi badh jaati hai (zyada gas paani me ghul jaati hai).
