9. Types of liquids
1. Volatile : Liquids which can convert to vapors.
2. Non Volatile : Liquids which can not convert to vapors.
Dilute Solutions/ Liquids
11. ❏ Since the surface particles are not very tightly held, they
will be converted to gaseous form.
❏ If the container is open, all the gaseous particles will
escape and with due time, the complete liquid will be
vaporised.
Vapour pressure of volatile liquids P0
12. ❏ If the container is closed, an equilibrium will be established
where the liquid will be converted to vapors, the vapors will go
toward the lid and thus they will condense back to liquid
❏ Liquid ⇆ Vapors
❏ Both evaporation and condensation processes are in
equilibrium.
❏ At a constant temperature, the pressure exerted by vapors of a
substance when it is in equilibrium with its liquid state is
called its vapor pressure.
❏ Pressure exerted by the vapors of the liquid =
VP of that Liquid at that temperature
Vapour pressure of volatile liquids P0
13. For a pure Volatile liquid,
VP i The VP does not depend on:
➢ the amount of liquid
➢ Shape of vessel
➢ Size of vessel etc.
● If surface area is more, evaporation will be more.
● At the same time, if amount of gaseous particles will be more, their
interaction will be more and thus condensation will be more.
● So, VP is same.
Vapour pressure of volatile liquids P0
14. For a pure Volatile liquid,
❏ Vapor Pressure depends only and only on TEMPERATURE.
❏ Relationship between Keq and VP
Liquid ⇆ Vapor
Keq = Partial pressure of vapor/ concentration of liquid
= PP of vapor
= VP of Liquid
Vapour pressure of volatile liquids P0
16. For a pure Volatile liquid,
Relationship between the VP of liquid and temperature is given as:
Where,
P1 is the VP at temperature T1 K
P2 is the VP at temperature T2 K
Enthalpy of vaporization in J/mol or Cal/mol
Clausius- Clapeyron Equation
18. The temperature at which the vapor pressure of a volatile liquid becomes
equal to the external pressure.
If external pressure is 1 bar, the boiling point is STANDARD BOILING
POINT.
If the external pressure is 1 atm, the boiling point is known as NORMAL
BOILING POINT.
Boiling Point
19. ❏ For different liquids at same temperature,
The vapor pressure depends upon the intermolecular attractive forces.
❏ If intermolecular forces of attraction are strong, VP will be less and thus
Boiling point will be more.
❏ At same temperature, If VP of a liquid is high, it will be a more volatile
liquid, hence will have a less boiling point.
Boiling Point
21. ❏ If on mixing two liquids A and B, the solution formed has the same
magnitude of force of interactions as there were in individual solvents,
the solution will be termed as ideal solution.
❏ If A-A = B-B = A-B, then the solution will be IDEAL SOLUTION.
Ideal Solutions
22. ❏ Since A-A = B-B = A-B, so
Va + Vb = Vsolution, so ΔVmix = 0
❏ Since A-A = B-B = A-B,
so ΔHmix = 0
Ideal Solutions
23. ❏ Since both the pure liquids are changing to mixtures, ΔSmix >0
❏ Since the solution is being formed, so the process is spontaneous so
ΔGmix <0
❏ Ideal solutions are just hypothetical. But some liquids can form
nearly ideal solutions.
❏ Benzene and toluene, n hexane and n heptane, chlorobenzene and
bromobenzene.
Ideal Solutions
25. ❏ Applicable for only IDEAL LIQUID SOLUTIONS.
❏ In an Ideal solution at a constant temperature, the vapor pressure
of a particular liquid is directly proportional to the mole fraction of
that liquid in that solution.
Raoult’s law
26. ❏ Both liquids A and B will be
vaporised and will be converted
to their vapor state.
❏ After some time vapors of A will
establish equilibrium with Liq A
and vapors of B will establish
Equilibrium with Liq B
Raoult’s law for Binary Ideal solution
27. ❏ Let PA and PB be the vapor pressure of A and B resp. In solution
phase.
❏ According to Raoult’s law
PA∝ XA so, PA= P0
AXA
PB∝ XB so, PB= P0
BXB
Where XA and XB are the mole fractions of liquids in the solution.
And
P0
A and P0
B are the vapor pressure of pure A and B resp. at a particular
temperature.
Raoult’s law for Binary Ideal solution
28. ❏ Since XA and XB are both less than 1, thus
so, PA < P0
A and PB < P0
B
This is because now the surface of the solution is occupied by the molecules
of both A and B , thus both the molecules will compete with each other to go
to the vapor phase.
❏ The total vapor pressure of the solution will be equal to the sum of VP
of both the volatile liquids present in the solution.
Psol = PA + PB
Psol = P0
AXA + P0
BXB
Raoult’s law for Ideal Binary solutions
29. The vapor phase contains the vapors of both A and B, so DALTON’S LAW can
be applied.
Psol = PT= PA + PB
Since, PP = TP*mole fraction of the gas
So,
PA = PT* YA
PB = PT* YB
Where
YA and YB are the mole fraction of gases in the vapor phase.
Also
YA + YB =1
Vapor phase composition
34. Considering A as more volatile than B
Psol = P0
AXA + P0
BXB
Psol = P0
AXA + P0
B(1-XA)
Psol = (P0
A-P0
B)XA + P0
B
Equating it with y= mx+c
m = P0
A-P0
B
c = P0
B
Both slope and intercept will be positive
Graphical representation of Raoult’s Law
39. Since 1/PT v/s YA graph is an
increasing graph,
So the graph of PT v/s YA has to
be a decreasing graph and the
graph will be a parabolic graph.
Graphical Representation: Other form of Raoult’s Law
41. This type of graph is very useful for
studying
DISTILLATION
1. The area enclosed by the curve
has both liquid and vapor in
equilibrium.
1. Since l ⇆ v, also in the upper
region pressure is high, so
according to Le Chatelier's
Principle, if P is increased,
equilibrium goes to the side with
less volume, so in the upper
region, we have liquid (less
volume) and in the lower region
we have vapor (more volume).
Graphical Representation: Combined Graph for YA and X
A
45. 1. The component that has
high VP will have a low
boiling point.
2. Also both the curves will
not be straight lines now.
3. The region bounded by the
curve is liquid in
equilibrium with vapor
4. Wrt equilibrium, upper part
is at higher temperature, so
it will be of vapors
5. Lower part is at lower
temperature so that
represents liquid.
Graph at constant Pressure: Boiling point
graph
48. Distillation can be carried out in 2 ways
1. Constant temperature by varying the pressure.
2. Constant pressure by varying the temperature.
Distillation
49. If the mixture given is IDEAL
BINARY LIQUID MIXTURE,
Then we need to decrease the
pressure to convert it to vapor
state.
If the mixture given is IDEAL
BINARY GASEOUS MIXTURE,
then we need to increase the
pressure to convert it to liquid
state.
Distillation : At constant temperature, by
varying pressure
50. 1. Point A: System is in
liquid state.
2. AB: System is still in
liquid state.
3. Point B: First bubble of
vapor will be formed.
4. BC: Both liquid and vapor
will be in equilibrium.
5. Point C: Last drop of
liquid is left.
6. CD: System is in the
gaseous state.
Distillation : At constant temperature, by
varying pressure
51. Since A is more volatile so its mole fraction in the vapour state will
keep on increasing
After a number of distillation steps such vapours are obtained which
contain almost all A gaseous molecules while the liquid phase will
contain almost B liquid
Distillation Process
58. Solutions which do not follow Raoult’s LAW
There are two types of NON IDEAL solutions
Showing positive deviation from Raoult’s Law
Showing negative deviation from Raoult’s Law
Types of non Ideal Solutions
65. A binary solution containing two volatile liquids in which both liquid
and vapor composition have same values.
Azeotropes
66. Since the composition of mixture remains unchanged so the
azeotropic mixture will boil at constant temperature.
Components of an azeotropic mixture can not be separated by simple
or fractional distillation.
An Ideal solution can never form an azeotrope.
Azeotropes
67. ● The boiling point of azeotrope is lesser than that of both liquids.
● Formed by solutions showing LARGE POSITIVE DEVIATION
from ideal solution that too, only at a certain COMPOSITION.
● For azeotropic mixtures, the VP curve becomes irregular.
● The vapor pressure first increases and then decreases.
● At maximum VP, azeotrope will be formed.
● Since VP is maximum, the boiling point will be minimum.
● A solution of 96% ethanol and 4% water is an example of
minimum boiling azeotrope.
● If fractional distillation is carried out for such solutions, they will
always reach to azeotropic composition.
Minimum Boiling Azeotropes
71. ● The boiling point of azeotrope is more than that of both liquids.
● Formed by solutions showing LARGE NEGATIVE DEVIATION
from ideal solution that too, only at a certain COMPOSITION.
● For azeotropic mixtures, the VP curve becomes irregular.
● The vapor pressure first decreases and then increases.
● At minimum VP, azeotrope will be formed.
● Since VP is minimum, the boiling point will be maximum..
● A solution of 62% nitric acid and 32% water is an example of
maximum boiling azeotrope.
● If fractional distillation is carried out for such solutions, they will
always reach to azeotropic composition.
Maximum Boiling Azeotropes
73. Properties of dilute solution containing non volatile solute which
depends upon number of solute particles in the solution.
1. Solute has to be non volatile
2. Solvent has to be volatile
3. Solution should be dilute
4. Since solute is very less, so dilute solution of non volatile solute
can be considered to be nearly Ideal solution.
5. Raoult’s law can be used.
6. These properties do not depend upon nature of solute but may
depend upon the nature of solvent.
Colligative Properties
74. 1. Relative lowering of vapor pressure
2. Elevation in boiling point
3. Depression in freezing point.
4. Osmotic Pressure
Property 2 and 3 depend on the nature of solvent.
Property 1 and 4 do not depend on the nature of solvent.
Colligative Properties
83. On adding non volatile solute to a volatile solvent, the vapor pressure
of the solvent decreases, so to make it reach to external pressure,
more temperature is required.
Thus boiling point increases
Elevation in Boiling Point
87. Freezing point:
The temperature at which the vapor pressure of liquid becomes equal
to the vapor pressure of the solid.
On adding non volatile solute, since the vapor pressure of solvent
decreases thus the freezing point will also decrease.
Depression in freezing point
96. When a liquid solution containing non volatile solute and pure solvent
are separated by a semipermeable membrane, then there is a natural
tendency of solvent particles to pass through the semipermeable
membrane, from PURE SOLVENT to SOLUTION.
Only solvent particles can pass through SPM
Osmosis
98. ● When a liquid solution containing non volatile solute and pure
solvent are separated by a semipermeable membrane, then
there is a natural tendency of solvent particles to pass through
the semipermeable membrane, from PURE SOLVENT to
SOLUTION.
● The movement of solvent particles continues equilibrium is
achieved.
● Only solvent particles can pass through SPM
● Solvent moves from a region of high solvent concentration
(dilute) to a region of low solvent concentration (conc)
Osmosis
99. ● The equilibrium hydrostatic pressure developed at the liquid
solution side due to osmosis
Osmotic Pressure
101. ● The external pressure that should be applied on the solution side
to prevent osmosis
Osmotic Pressure
102. ● If the applied external pressure is greater than the osmotic
pressure, then the solvent particles will move from the solution
side to solvent side through SPM.
● Used in water purification to remove dissolved impurities from
water.
Reverse Osmosis
108. ● ISOTONIC SOLUTIONS: If two solutions have same Osmotic
pressure
● HYPERTONIC: The solution with higher OP
● HYPOTONIC: The solution with lower OP
Isotonic, hypertonic, hypotonic solutions
109. [Main April 12, 2019 (II)]
A.
B.
C.
D.
8.2 atm
2.46 atm
4.92
1.64 atm
112. ● Some solutes undergo dissociation or association when dissolved
in a solvent.
● In such cases, the actual number of solute particles present in
the solution become different compared to the theoretical
number of solute particles.
Vant’s Hoff Factor (i)
121. Since gas and liquid are in contact with each other, there will be
diffusion of gas in the liquid
A liquid solution will be formed, where gas acts as solute and liquid
acts as solvent.
Solubility of gas in liquid
122. SOLUBILITY OF GAS : At a constant temperature, the maximum
amount of the gas that can be dissolved in a fixed amount of liquid
Solubility of gas in liquid
123. Temperature: Lower temperature favors solubility of gas
Pressure: Higher pressure favors solubility.
Solubility of gas in liquid
To increase the solubility of CO2 in soft drinks and soda water, the
bottle is sealed under high pressure.
124. Relation between dissolved amount of gas in liquid and pressure
At constant TEMPERATURE, the mole fraction of gas in the liquid is
directly proportional to the pressure of that gas present above the
liquid.
Henry’s law
133. Applications of Henry’s law
To increase the solubility of CO2 in soft drinks and soda water, the
bottle is sealed under high pressure.
134. Applications of Henry’s law
Scuba divers must cope with high concentrations of dissolved gases
while breathing air at high pressure underwater. Increased pressure
increases the solubility of atmospheric gases in blood. When the
divers come towards surface, the pressure gradually decreases. This
releases the dissolved gases and leads to the formation of bubbles
of nitrogen in the blood. This blocks capillaries and creates a medical
condition known as bends, which are painful and dangerous to life.
To avoid bends, as well as, the toxic effects of high concentrations
of nitrogen in the blood, the tanks used by scuba divers are filled
with air diluted with helium (11.7% helium, 56.2% nitrogen and
32.1% oxygen).
135. Applications of Henry’s law
At high altitudes the partial pressure of oxygen is less than that at
the ground level. This leads to low concentrations of oxygen in the
blood and tissues of people living at high altitudes or climbers. Low
blood oxygen causes climbers to become weak and unable to think
clearly, symptoms of a condition known as anoxia.
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