CHAPTER
2 Solutions
Concentration Term Relative Lowering of Vapour Pressure
Number of moles of solute The vapour pressure of the solvent is lowered by the presence of
Molality (m) =
Weight of solvent (kg) a non-volatile solute in the solution and this lowering is governed
Number of moles of solute by Raoult's law, according to which relative lowering of vapour
Molarity (M) =
Volume of solution (L) pressure of solvent is equal to the mole fraction of non-volatile
Number of gram-equivalents of solute solute present in solution.
Normality (N) = Relative lowering of vapour pressure = χB
Volume of solution (L)
PºA – PS
Formality (F) =
Number of gram-formula mass of solute = χB {χB = mole fraction of solute}
Volume of solution (L) PºA
PPM = mass fraction × 106 Elevation of boiling point
Henry’s Law ∆Tb = Kb × m {m = molality}
The dissolution of a gas in a liquid is governed by Henry’s law, RTb2 M A RTb2
=
according to which, at a given temperature, the solubility of a K b =
1000 L vapourisation 1000∆H vapourisation
gas in a liquid is directly proportional to the partial pressure of
the gas. where Lvapourisation is latent heat of vapourisation in cal./g
p = partial pressure of gas in vapour phase ∆Hvapourisation is enthalpy of vapourisation in cal./mol
=
p K= H .X K
H Henry 's law constant Depression in freezing point
X = Mole fraction of gas
∆Tf = Kf × m
Clausius - Clapeyron Equation
RTf2 M A RTf2
P ∆H vapour 1 1 = Kf =
log 2 = – 1000 Lfusion 1000∆H fusion
P1 2.303R T1 T2
where, P1, P2 are vapour pressure of liquid at T1 and T2 where Lfusion is latent heat of fusion in cal./g
respectively. ∆Hfusion is enthalpy of fusion in cal./mol
Roult's Law Osmotic pressure
PT = PºA χ A + PºB χ B (Solution) π = CRT
For isotonic solution, π1 = π2 thus, C1 = C2.
PA PºA χ A
Y==
A
PT PºA χ A + PºB χ B Van’t Hoff Factor
{YA; YB = mole fraction of A and B in vapour phase Van’t Hoff Factor ‘i’ is the extent to which a solute is dissociated
PT = PA + PB or associated. This can be defined as ratio of observed colligative
property to calculated colligative property.
Colligative Properties
Experimental colligative property (observed)
These are the properties of solutions which depends on the number i=
of solute particles and independent of their chemical identity. Calculated colligative property(Normal)
These are relative lowering of vapour pressure, elevation in Theoritical molar mass of solute
i=
boiling point, depression in freezing point and osmotic pressure. Actual / observed molar mass of solute
2 Solutions
Concentration Term Relative Lowering of Vapour Pressure
Number of moles of solute The vapour pressure of the solvent is lowered by the presence of
Molality (m) =
Weight of solvent (kg) a non-volatile solute in the solution and this lowering is governed
Number of moles of solute by Raoult's law, according to which relative lowering of vapour
Molarity (M) =
Volume of solution (L) pressure of solvent is equal to the mole fraction of non-volatile
Number of gram-equivalents of solute solute present in solution.
Normality (N) = Relative lowering of vapour pressure = χB
Volume of solution (L)
PºA – PS
Formality (F) =
Number of gram-formula mass of solute = χB {χB = mole fraction of solute}
Volume of solution (L) PºA
PPM = mass fraction × 106 Elevation of boiling point
Henry’s Law ∆Tb = Kb × m {m = molality}
The dissolution of a gas in a liquid is governed by Henry’s law, RTb2 M A RTb2
=
according to which, at a given temperature, the solubility of a K b =
1000 L vapourisation 1000∆H vapourisation
gas in a liquid is directly proportional to the partial pressure of
the gas. where Lvapourisation is latent heat of vapourisation in cal./g
p = partial pressure of gas in vapour phase ∆Hvapourisation is enthalpy of vapourisation in cal./mol
=
p K= H .X K
H Henry 's law constant Depression in freezing point
X = Mole fraction of gas
∆Tf = Kf × m
Clausius - Clapeyron Equation
RTf2 M A RTf2
P ∆H vapour 1 1 = Kf =
log 2 = – 1000 Lfusion 1000∆H fusion
P1 2.303R T1 T2
where, P1, P2 are vapour pressure of liquid at T1 and T2 where Lfusion is latent heat of fusion in cal./g
respectively. ∆Hfusion is enthalpy of fusion in cal./mol
Roult's Law Osmotic pressure
PT = PºA χ A + PºB χ B (Solution) π = CRT
For isotonic solution, π1 = π2 thus, C1 = C2.
PA PºA χ A
Y==
A
PT PºA χ A + PºB χ B Van’t Hoff Factor
{YA; YB = mole fraction of A and B in vapour phase Van’t Hoff Factor ‘i’ is the extent to which a solute is dissociated
PT = PA + PB or associated. This can be defined as ratio of observed colligative
property to calculated colligative property.
Colligative Properties
Experimental colligative property (observed)
These are the properties of solutions which depends on the number i=
of solute particles and independent of their chemical identity. Calculated colligative property(Normal)
These are relative lowering of vapour pressure, elevation in Theoritical molar mass of solute
i=
boiling point, depression in freezing point and osmotic pressure. Actual / observed molar mass of solute
