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IMPORTANT QUESTIONS WITH ANSWERS
PHYSICAL PHARMACEUTICS- I (BP302T)
UNIT-I
Q.1 State Raoult’s law. What do you understand by ideal and real solution?
Answer:
RAOULT’S LAW
• “The partial pressure of each component in a solution is directly proportional to the vapour pressure of
the corresponding pure substance and that the proportionality constant is the mole fraction of the
component in the liquid.”
• For a binary solution having volatile components A and B:
PA0 α PA and PB0 α PB
Then, PA0 = PAXA and PB0 = PBXB
where, PA0= partial pressure of A, PB0 = partial pressure of B
PA= vapour pressure of A, PB=vapour pressure of B
XA= mole fraction of A, XB= mole fraction of B
IDEAL AND NON-IDEAL SOLUTIONS
Ideal solutions
Definition: solution which obeys
Raoult’s law over the entire range of
concentration and temperature and during
the formation of which no change in
enthalpy and no change in volume takes
place.
Non-ideal solutions
Definition: The solutions which do not obey Raoult’s law and are
accompanied by change in enthalpy and change in volume during their
formation are called non-ideal solutions.
Solutions with positive
deviations
Solutions with negative
deviations
A……B interactions are similar to
A……A and B……B interactions
A……B interactions are smaller
than A……A and B……B
interactions
A……B interactions are greater
than A……A and B……B
interactions
PA0 = PAXA and PB0 = PBXB .
PA0 > PAXA and PB0 >PBXB .
PA0 < PAXA and PB0 < PBXB .
Hsolution = 0
Hsolution> 0
Hsolution< 0
Vmixing = 0
Vmixing> 0
Vmixing< 0
Do not form azeotrope
form minimum boiling point
azeotrope
form maximum boiling azeotrope
Examples: Chlorobenzene and
bromobenzene, Benzene and toluene
Examples: ethanol and water,
methanol and water
Examples: acetic acid and
pyridine, HCl and water
Q.2 Explain ideal solubility parameters. What are its applications, advantages and limitations?
Answer:
IDEAL SOLUBILITY PARAMETERS:
• To estimate solubility as a result of solute- solvent interactions, some ideal solubility parameters are
required, which are very well explained by “Regular Solution Theory”. This theory suggests a
numerical estimation about solubility-
δ1 = ( ΔU/V )1/2 = [(ΔH-RT) / V]1/2
where, δ1 = solubility parameter
ΔU = molar energy, V = molar volume of solvent, ΔU/V = cohesive energy density of solvent
ΔH = molar heat of vaporisation of solvent, R = gas constant, T = temperature
• The difference between δ1 and δ2 (δ1 - δ2) gives the numerical value for solubility.
• Unit of solubility parameters:
1). Conventional- (Cal/ cm3)1/2 or Cal1/2cm-3/2
