Solubility of liquids in liquids, The term miscibility refers to the mutual solubility of the component of liquid - liquid system, Raoult’s Law, Raoult’s law may be mathematically expressed as: Ideal solution, Real solution

1. IIIrd Semesester B. pharmacy
Physical Pharmaceutics-I
Unit-I
Solubility of drugs(Part-7)
(Solubility of liquids in liquids)
Presented By :
Miss. Pooja D. Bhandare
(Assistant Professor)
Kandhar College of Pharmacy, Nanded

2.  SOLUBILITY OF LIQUIDS IN LIQUIDS
• PREPARATION OF PHARMACEUTICAL SOLUTIONS INVOLVES MIXING OF TWO OR MORE
LIQUIDS.
1. ALCOHOL & WATER TO FORM HYDRO-ALCOHOLIC SOLUTIONS.
2. VOLATILE OIL & WATER TO FORM AROMATIC WATERS
3. VOLATILE OIL & ALCOHOLS TO FORM SPRITS, ELIXIRS
• LIQUID – LIQUID SYSTEM MAY BE DIVIDED INTO 2 CATEGORIES
SYSTEM SHOWING COMPLETE MISCIBILITY SUCH AS ALCOHOL & WATER, GLYCERINE &
ALCOHOL, BENZENE AND CARBON TETRACHLORIDE.
SYSTEM SHOWING PARTIAL MISCIBILITYAS PHENOLAND WATER; TWO LIQUID LAYER
ARE FORMED EACH CONTAINING SOME OF THE OTHER LIQUID IN DISSOLVE STATE.

3. THE TERM MISCIBILITY REFERS TO THE MUTUAL SOLUBILITY OF THE
COMPONENT OF LIQUID - LIQUID SYSTEM
• IF THE SOLVENT IS A & OTHER SOLVENT B AND THE FORCES OF ATTRACTION ARE
REPRESENT BY A-A, B-B AND A-B.
• COMPLETE MISCIBILITY OCCURS WHEN : THE ADHESIVE FORCES BETWEEN DIFFERENT
MOLECULE (A-B) > > COHESIVE FORCES BETWEEN LIKE MOLECULE (A-A OR B-B).
• POLAR AND SEMI-POLAR SOLVENT, SUCH AS WATER AND ALCOHOL, GLYCERIN AND
ALCOHOL, ALCOHOL AND ACETONE ARE SAID TO BE COMPLETELY MISCIBLE BECAUSE
THEY MIX ALL PROPORTION.
• NON- POLAR SOLVENTS SUCH AS BENZENE AND CARBON TETRACHLORIDE ARE
COMPLETELY MISCIBLE.

4. • BINARY SOLUTION IS A MIXTURE OF TWO LIQUIDS THAT ARE COMPLETELY MISCIBLE
ONE WITH ANOTHER. THE BOILING POINT OF BINARY SOLUTION DEPENDS UPON THE
SOLUTION COMPOSITION.
RAOULT’S LAW
• RAOULT’S LAW STATES THAT THE PARTIAL VAPOUR PRESSURE OF EACH VOLATILE
CONSTITUENT IS EQUAL TO THE VAPOUR PRESSURE OF THE PURE CONSTITUENT
MULTIPLIED BY ITS MOLE FRACTION THE SOLUTION, AT GIVEN TEMPERATURE.
• A MIXTURE OF MISCIBLE LIQUIDS AAND B ARE CONSIDERED.

5. • IN THIS MIXTURE
LET PARTIAL VAPOUR PRESSURE EXERTED BY LIQUID A = PA KILOPASCALS (KPA)
let partial vapour pressure exerted by liquid B = pB (kPa)
let partial vapour pressure exerted by pure liquid A = p°A (kPa)
let partial vapour pressure exerted by pure liquid B = p°B (kPa)
LET MOLE FRACTION CONCENTRATION OF A IN LIQUID = XA
let mole fraction concentration of A in liquid = XB

6. • RAOULT’S LAW MAY BE MATHEMATICALLY EXPRESSED AS:
Partial vapour pressure Vapour pressure of mole fraction
of a liquid pure liquid of liquid
PA p°A XA
pB p°B XB
• Total vapour pressure : PA pB (p°A XA) (p°B XB)
• SOME CONCEPT
 Total of mole fraction is always 1.
IF MOLE FRACTION OF LIQUID ‘A’ IS 0.7 THEN THE MOLE FRACTION OF LIQUID ‘B’ IS 0.3

9. • PA = P°A XA AND PA = P°A XB
• THE SOLUTE-SOLVENT FORCES OF ATTRACTION IS A – B = A-A OR B – B
• THE ENTHALPY OF MIXING OF TWO COMPONENTS SHOULD BE ZERO, THAT IS, . ΔMIX
H=0. THIS SIGNIFIES THAT NO HEAT IS RELEASED OR ABSORBED DURING MIXING OF TWO
PURE COMPONENTS TO FORM AN IDEAL SOLUTION.
• THE VOLUME OF MIXING IS EQUAL TO ZERO THAT IS, Δ MIXV=0. THIS MEANS THAT TOTAL
VOLUME OF SOLUTION IS EXACTLY SAME AS THE SUM OF THE VOLUME OF SOLUTE AND
SOLUTION.

10. • PA> P°A XA AND PB> P°B XB , AS THE TOTAL VAPOUR PRESSURE (P°A XA + P°B XB ) IS
GREATER THAN WHAT IT SHOULD BE ACCORDING TO RAOULT’S LAW.
• THE SOLUTE-SOLVENT FORCES OF ATTRACTION IS WEAKER THAN SOLUTE-SOLUTE AND
SOLVENT-SOLVENT INTERACTION THAT IS, A-B < A-A OR B-B.
• THE ENTHALPY OF MIXING IS POSITIVE THAT IS ΔMIX H >0 BECAUSE THE HEAT ABSORBED
TO FORM NEW MOLECULAR INTERACTION IS LESS THAN THE HEAT RELEASED ON
BREAKING OF ORIGINAL MOLECULAR INTERACTION.
• THE VOLUME OF MIXING IS POSITIVE THAT IS, ΔMIX V >0 AS THE VOLUME EXPAND

11. IDEAL SOLUTION
• AN IDEAL SOLUTION IS DEFINED AS THE SOLUTION IN WHICH NO VOLUME OR
TEMPERATURE CHANGE OCCURS ON MIXING OF THE TWO LIQUIDS AND WHICH
COMPLETELY OBEY RAOULT’S LAW.
REAL SOLUTION
• AN REAL SOLUTION IS DEFINES AS THE SOLUTION IN WHICH CHANGE IN VOLUME OR
CHANGE IN TEMPERATURE OR BOTH WHILE MIXING OF TWO LIQUIDS AND DO NOT
OBEY RAOULT’S LAW

12. THANK YOU!