Solutions

Gas in solid  Solution of hydrogen in palladium

Solid Solutions
Liquid in solid  Amalgam of mercury with sodium
Mass %, ppm, mole fraction and molality are independent of temperature, whereas
Temp. Vs Conc.
molarity depends on temperature. This is because volume depends on temperature.
At a constant temperature, the solubility of a gas in a liquid is directly proportional to the
Henry’s law. pressure of the gas. p = KH . x
KH = Henry’s law constant ( greater the KH value means lower the solubility.)
1.To increase the solubility of CO2 in soft drinks, the bottle is sealed under high pressure.
Application of Henry’s law.
2. To avoid bends, the tanks used by scuba divers are filled with air diluted with helium
Solubility of gas increases with decrease of temperature. It is due to this reason that
Temp and Solubilty of gas
aquatic species are more comfortable in cold waters rather than in warm waters.
Raoult’s law for volatile The partial vapour pressure of each component in the solution
liquids is directly proportional to its mole fraction p1 α x1 p1 = p10 x1
The solutions which obey Raoult’s law over the entire range of concentration are known
Ideal Solutions as ideal solutions. ( For ideal solution ΔmixH = 0, ΔmixV = 0)
Example : Solution of n-hexane and n-heptane,
Positive deviation : A-B interactions are weaker than those between A-A or B-B,
Example - Mixtures of ethanol and acetone
Non-ideal Solutions
Negative deviations : Forces between A-A and B-B are weaker than those between A-B
Example- mixture of phenol + aniline. a mixture of chloroform +acetone
Mixtures have same composition in liquid and vapour phase and boil at a constant temp.
Azeotropes minimum boiling azeotrope(positive deviation) eg- 95% aq ethanol
maximum boiling azeotrope(negative deviation) eg- 68% aq nitric acid
Colligative properties Depend on the number of solute particles not upon their nature.

Relative Lowering of
Vapour Pressure

Elevation of Boiling Point

Depression of Freezing Point

Osmosis Solvent flows through the semi permeable membrane from pure solvent to the solution.
The extra pressure applied on the solution that just stops the flow of solvent is called
Osmotic pressure
osmotic pressure of the solution

Osmotic pressure(π)

Isotonic solutions Two solutions having same osmotic pressure

Hypertonic Higher osmotic pressure than a particular soln
Hypotonic Lower osmotic pressure than a particular soln
The direction of osmosis can be reversed if a pressure larger than the osmotic pressure is
Reverse Osmosis applied to the solution side. That is, now the pure solvent flows out of the solution
Application : Desalination of sea water
ratio of normal molar mass to experimentally determined molar mass or as the ratio of
van’t Hoff factor ( i )
observed colligative property to the calculated colligative property.
NaCl, KCl = 2 ; BaCl2 CaCl2 = 3 ; Na3PO4 = 4 ; Al2(SO4)3 , K4[Fe(CN)6] = 5
Value of van’t Hoff factor(i)
CH3COOH ( in benzene) = 1/2
Some basic formulae: -
 Mass percentage. w/w Mole fraction Molarity (M) =
% For solvent XA=nA/nA+nB no. of moles of
For solute XB=nB/nA+nB solute/volume of solution (L)
XA+ XB = 1 Unit=mole/litre [mol/L]
ppm (parts per million)=
Molality (m) =
For liquid solutions
no. of moles of solute/mass
v/v % = mass of solute of solvent(kg)
Unit=mole/Kilogram
𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓
(WB)x106/total mass of
[mol/kg]
𝑠𝑜𝑙𝑢𝑡𝑒(𝑉𝐵)
solution (WA+WB)

𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛(𝑉𝐴
+ 𝑉𝐴)
NOTE:, mole fraction, mass percentage, ppm and molality are independent of
temperature, whereas molarity depends on temperature. This is because volume
depends on temperature.
SOLUBILITY (maximum amount of solute present in a specific amount of solvent at a
specified temperature) of gas depends on:

Nature of Pressure Temperature and Solubility of gas

gas
Easily Increases with increases with decrease in temperature,
liquefiable, increase in aquatic species are more comfortable in cold water
Easy to pressure rather than in warm water and prefer to stay at
dissolve (HENRY’S LAW) lower level away from the upper layer of water in
summers.
Henry’s law: -
Statement: - Mole fraction of gas in the solution is directly proportional to partial
pressure of gas in the vapour phase.
p  XB p= KHXB ( KH= Henry’s constant )(greater the KH value lower the
solubility)
APPLICATIONS: Soft drinks are sealed under high pressure to increase solubility of
CO2.
To avoid BENDS, the tanks used by scuba divers are filled with air diluted with helium
(less soluble than N2)

ANOXIA problem at higher altitudes due to low pressure low concentration of O2 in

Blood cells.

Raoult’s law: - The partial vapour pressure of each component in the solution is directly
proportional to its mole fraction. [ PA  X A and PB  X B ]
Ideal solutions Non-Ideal solutions
Obeys Raoult’s law over the entire range of Don’t Obey Raoult’s law
concentration
e.g. Solution of n-hexane and n-heptane
A-A , B-B = A-B interactions A-A , B-B ≠ A-B interactions
PTotal= PA+ PB PTotal= P AΧA+ PB ΧB
0 0 PTotal≠ PA+ PB PTotal≠ P0AΧA+ PB0ΧB
Δmix H= 0 Δmix V = 0 Δmix H≠ 0, Δmix V ≠ 0
Can be separated by fractional distillation Cannot be separated by fractional
distillation
Non-Ideal solutions
Positive deviation Negative deviation
PTotal > PA+ PB ΔVmix=+ve ΔHmix=+ve PTotal< PA+ PB ΔVmix=-ve
ΔHmix=- ve
A – B interaction is weaker than A – A and B – B A – B interaction is stronger than
interactions. A – A and B – B interaction
Minimum boiling Azeotrope* Maximum boiling Azeotrope
e.g. water + alcohol e.g. water+ HNO3

Azeotrope* Mixtures having same composition in liquid and vapour phase, boil at a
constant temperature and cannot be separated by fractional distillation.
Colligative properties: -
The properties of solutions
which depend only on the
number of particles of the
solute (molecules or ions) d
and do not depend on the
nature of solute.

Relative lowering Elevation in boiling Depression in Osmosis

in point freezing point
vapour pressure
ΔTb =Tb-𝑻𝒐 ΔTf =Tf-𝑻𝑶
𝒃 𝒇
poA-ps/poA=XB π=CRT

ΔTb=Kb m ΔTf = Kf m π=n/V×RT

.
The excess pressure on
solution side which just

Kb = molal elevation Kf = molal prevents the flow of

or EBULLIOSCOPIC depression or solvent molecules is

constant. It is the CRYOSCOPIC called OSMOTIC

elevation in boiling constant. It is the PRESSURE.

[for a very dilute point of 1 molal depression in
solution solution. freezing point of 1
nB << nA ] molal solution.

𝑝𝑜 − 𝑝 𝑛 𝑤2/𝑀
1 1 2 2
𝑝𝑜 𝑛1
= =
𝑤1/𝑀1 1

Condition for Reverse osmosis: pressure

higher than the osmotic pressure is applied on
the solution
The solvent will flow from the solution into the
pure solvent through the semi-permeable
membrane cellulose acetate)
Used in desalination of sea water,
Osmosis in plants and animal cells:
Antifreeze agent: ethylene glycol used in car radiators at hill stations (Depression in freezing
point)
De-icing agents: common salt (NaCl) or calcium chloride (CaCl2) is scattered on the roads to
melt ice in cold countries (Depression in freezing point)
 Edema: Due to excess intake of salt by a person, the tissues become puffy, it is called
edema. It is due to retention of water in the tissue owing to osmosis.
 Van’t Hoff factor: i = normal molar mass/abnormal(observed)molar mass

PROPERTY ASSOCIATION DISSOCIATION

1. Elevation in boiling point
ΔTb= iKb m
No. of Less more
molecules
2. Depression in freezing point Colligative Lowers Increases
ΔTf = i Kf m
property
Molar mass Greater than lesser
3. Osmotic pressure
π= iCRT
theoretical
value

𝑖−1 𝑖−1
i=1 i Less than 1 i More than 1

𝑛 − 1
(extent)

1
=degree of
−1
dissociation /
𝑛
[n = no. of
association dissociated
[n = no. of particles.]
particles
associated]

Q 1 X and Y liquids on mixing produces cold solution. What type of deviation is shown
by them?
Ans Positive deviation
Q 2 Aquatic species are more comfortable in cold waters rather than in warm waters.
Give reason.
Ans Solubility of gases increases with decrease in temperature as it is an exothermic
process.
Q3) What is the significance of Henry’s Law constant K H?
Ans a) Henry’s Law constant (KH) helps in comparing the relative solubilities of
different gases in the same solvent (e.g. water). In general, the lesser the value of
KH, the more the solubility of a gas.

Q.4) How the colligative properties change if the solute undergo dissociation in
solution?
Ans increases due to increase in number of particles on