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Solutions IV
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Raoult's Law and Dalton's law

Shaillee Kaushal is teaching live on Unacademy Plus

Shaillee Kaushal
Faculty in Chemistry with a teaching experience of 14 years. Specialised in teaching for boards and competitions.

Unacademy user
  1. XII 02 Solutions IV

  2. SOLUTIONS OF LIQUIDS IN L OU DS When one liquid dissolves in other there are certain changes which are taking place in both the solute and the solvent. The molecule of the solvent moves apart so as to make spaces for incoming solute particles and the solute particles are also separated so as to take their space in the solvent. The overall desolution process results either in evolution of heat or absorption of heat or there may be not changes at all. Example:s 1. Benzene and CCI4 2. Acetone and H20 No evolution or absorption of heat. Evolution of heat Absorption of heat 3. Ethyl alcohol and water

  3. Liquid in Liquid solutions 1Liquids that are Completely miscible.miscible E.g Benzene Toulene Ethyl alcohol+ water Pheno H20 2. Liquids that are partially 3. Immiscible Benzene + H20 Benzene + E.g. E.g. Ether H20 CCI4 + H20 alcohol CCl4 Benzene Nicotine H20

  4. Ideal solution: Those solutions is which the forces between A and B, B and B and A and B are all same are called ideal solutions For such solutions = 0 mix V solvent +V solute = V solution. mix This means that neither heat is absorbed nor evolved during mixing There should be no chemical reaction between solvent and solute. Solute particles should neither associate nor dissociate in ideal solution. Ideal solutions must obey Raoult's law. Examples: (i) Benzene and Toulene (ii) n-Hexane and n-Heptane (iii) Ethylene dibromide and ethylene dichloride

  5. Raoults's law: The partial pressure of any volatile costituent of a solution is equal to the vapour pressure ofpure constituent multiplied bythe mole fraction of that constituent in the solution. In a binary solution A-B PAand Pp pressure of the two constituents. XA and XB-mole fraction of the two constituents

  6. Thus according to Raoult's law: Total pressure

  7. Positive deviation Negative Deviation Do not obey Raoult's law 1. do not obey Raoult's law 2. H> O Endothermic dissolution H< 0 exothermic dissolution mix mix mix mix PA < Pe.NAPg < P8.xB AXA B.XB 5. A-B interactions are weaker than A-A and A-B interactions are stronger than A-A and B-B interatctions B-B attractive forces Examples Acetone +chloroform Acetone +chloroform CH3 OH chloroform H20 HNO3 Examples Acetone +ethanol Acetone CS2 Water+methanol CCl4 toulene

  8. Graphically the ideal and non ideal solutions can be represented as Ideal deviation Positive deviation egative deviation Total vapour Ideal XA1 Mole fraction XA-0 Xy=0 XA-1 Mole fraction Xg-1 Xy=0 Xi=1 XB-0 Mole fraction XB:0 :0

  9. Relation between Dalton's law and Raoult's law: Let the mole fractions of vapour A and B by y, and Yn respectively. Let Pa and P be the partial pressures of vapur A and B and total pressure be 'P PB YBPo - (ii) PAXAP (iii) - (1V Equating equation (i) and (iii 0 Similarly 0