Solutions
Prepared by
D S Samkutty,PGT Chemistry ,
JNV Pathanamthitta
SOLUTIONS
Solution is a homogeneous mixture of two or more
substances.
In binary solution the part which is present in larger
amount is called solvent and the part which is present in
lesser amount is called solute.
TYPES OF SOLUTION
SOLID SOLUTION ( Solid is the solvent) 1.gas in solid
2. liquid in solid
3. gas in solid
LIQUID SOLUTION ( Liquid is the solvent)1. gas in liquid
2 . liquid in liquid
3. solid in liquid
GASEOUS SOLUTION(Gas is the solvent)1. gas in gas
2. liquid in gas
3. Solid in gas
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TYPES OF SOLUTIONS
Gaseous solutions Liquid solutions Solid solutions
Gas in Gas Gas in Liquid Gas in solid
Liquid in Gas liquid in liquid Liquid in solid
Solid in Gas Solid in Liquid Solid in solid
Examples
Gaseous solutions
Gas in Gas- Air ( oxygen in nitrogen)
Liquid in Gas ( Chloroform in nitrogen)
Solid in gas ( Camphor in nitrogen)
Liquid Solutions
Gas in liquid (Oxygen in water )
Liquid in liquid ( ethanol in water )
Solid in liquid (glucose in water )
Solid solutions
Gas in solid ( Hydrogen in Palladium)
liquid in solid ( Mercuy in sodium)
solid in solid ( copper in gold)
WAYS OF EXPRESSING CONCENTRATIONS
( TEMPERATURE DEPENDANT) (TEMPERATURE INDEPENDENT)
VOLUME PERCENTAGE MASS PERCENTAGE
MASS BY VOLUME PERCENTAGE MOLE FRACTION
MOLARITY MOLALITY
NORMALITY ppm ( parts per million)
MASS PERCENTAGE (W/W)
Mass % = Mass of the component in the solution
----------------------------------------------------- X 100
Total mass of the solution
Mass percentage is the weight of the solute present per 100
units of the solution.
Eg: 10% glucose in water means 10 g of glucose in 90 g of water
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VOLUME PERCENTAGE (v/v)
volume of the component
Volume % = -------------------------------------- X 100
Total volume of solution
Eg : 10% ethanol solution in water means
ie 10 mL of ethanol is dissolved in 90 mL of water
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MASS BY VOLUME PERCENTAGE (w/v)
Mass of the solute
Mass /volume % = ----------------------------- X 100
total volume of the solution
Eg : 23% w/v glucose solution means 23 g of glucose dissolved in 100 mL of
water.
This unit is used in medicine and pharmacy
Parts per million(ppm)
Number of parts of the component
ppm = ------------------------------------------------------------------------------ X 106
Total number of parts of all components in the solution
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Mole fraction ( χ)
Number of moles of the component
Molefraction of a component = ---------------------------------------------------
total number of moles of all the components
ȠA
molefraction of A , XA =--------------------------
ȠA +ȠB
ȠB
molefraction of B, XB = -------------------------
ȠA + ȠB
XA + XB = 1
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MOLARITY(M)
It is defined as the number of moles of a solute dissolved in one
litre of the solution
number of moles of solute
M = -------------------------------------------------------
Total volume of the solution in litre
Mass of the solute x 1000
= ------------------------------------
Molar mass the solute x Volume of the solution in mL
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MOLALITY (m) :
It is defined as the number of moles of solute present in 1
Kg of the solvent
Moles of solute
Molality =--------------------------------
Mass of solvent in Kg
Mass of the solute x 1000
= ---------------------------------------------------
Molar mass of solute X Mass of solvent in g
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• SOLUBILITY
• solubility of a substance is its maximum
amount that can be dissolved in a specific amount
of solvent at a specified temperature.
• It depends on * nature of solute and solvent
* temperature
* Pressure
Polar solutes dissolve in polar solvents and nonpolar
solutes dissolve in nonpolar solutes.
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solute + solvent =solution
If the dissolution process is endothermic(ΔsolH>0 ) , the solubility
should increase with rise in temperature.
If the dissolution process is exothermic ( ΔsolH < 0) , the solubility
should decrease
Pressure does not have any significant effect on solubility of solids
in liquids.
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Henry’s law
Henrys law states that at a constant temperature,the
solubility of a gas in a iquid is directly proportional to the
pressure of the gas.
or
The law states that the partial pressure of the gas in vapour
phase(p) is proportional to the molefraction of the gas (x)in
the solution.
p= K H X
where KH is the Henrys law constant.
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Henrys law Graphical Representation
P = KH X
PARTIAL PRESSURE
SLOPE = KH
OF GAS
MOLE FRACTION OF GAS
IN SOLUTION
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APPLICATIONS OF HENRY’S LAW
1. Soft drinks :To increase the solubility of CO2 in soft
drinks and soda water ,the bottle is sealed under high
pressure.
2. Bends in scuba divers:
3. Anoxia : Low oxygen concentration in the bood of
mountainers or people living in high altitude
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RAOULTS LAW FOR VOLATILE COMPONENT
Raoults law states that for a solution of volatile liquids,the partial
pressure of each component in the solution is directly proportional
to its mole fraction.
pA = pA0 xA where pA0 is the vapour pressure of pure component A
pB = pB0 xB where pB0 is the vapour pressure of pure componentB
P total = pA + pB
= p0A +(p0B –p0A) xB
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RAOULTS LAW FOR NON-VOLATILE COMPONENT
If the component B ( solute ) is non volatile, it cannot give any
contribution to the total pressure of the solution
Then Ptotal = pA + pB
Psolution = pA + 0
= p0A(1-xB)
Δp/p0A = xB
ie For non-volatile solute Raoults law states that the relative lowering
of vapour pressure is equal to mole fraction of the solute
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IDEAL SOUTION
solutions which obey Raoults law
ΔV mixing =0
ΔH mixing =0
Here FA-A or FB-B = FA-B
eg: (a) solution of n-hexane and n-heptane
(b) solution of bromoethane and chloroethane
( c ) solution of benzene and toluene
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(NON-IDEAL SOLUTION)
SOLUTIONS SHOWING POSITIVE DEVIATION
• Do not obey Raouts law
• ΔV mixing >0
• ΔHmixing > 0
• Eg : mixture of cyclohexane and ethanol
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(NON-IDEAL SOLUTIONS)
SOLUTIONS SHOWING NEGATIVE DEVIATIONS
Do not obey Raoults law
ΔV mixing <0
ΔH mixing < 0
Eg : mixture of Acetone and chloroform
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Colligative properties
The properties which depends on the number of solute particles
not on the nature.
(1) Relative lowering of vapour pressure of the solvent (ΔP/P0)
(2 ) Elevation of boiling point of the solvent (ΔTb)
(3) Depression of freezing point of the solvent (ΔTf)
(4)Osmotic pressure of the solution (π)
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RELATIVE LOWERING OF VAPOUR PRESSURE:
when a non-volatile solute is added to a solvent its vapour
pressure is decreased.This is called lowering of vapour
pressure.
relative lowering of vp, ΔP
( ------) = XB
P0A
ΔP = P0A x XB
ΔP α XB
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Relation between lowering of vapour pressure and molar mass
According to Raoults law relative lowering of vapour pressure = molefraction of
the solute
ΔP
------ = XB , XB is the molefraction of the solute
P0A
substituting molality in the above equation
ΔP WB x MA
------ = ------------------
P0A MB x WA
(Colligative Proerty)
2.Elevation of Boiling Point (ΔTb):Then the difference between the
boiling points of the pure solvent and that of the solution is
called elevation of boiling point (ΔTb).
ΔTb=Tb - Tb0
ΔTb α molality
ΔTb = Kb x molality,
where Kb molal elevation constant
or Ebullioscopic constant
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Relation between Elevation of Boiling point and Molar mass of solute
ΔTb = Kb x molality
Kb x WBx1000
ΔTb =---------------------- WA- mass of solvent
MB x WA WB- mass of solute
MB- molar mass of solute
1000 Kb x WB ΔTb-elevation of boiling point
MB=----------------------
ΔTb x WA
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(colligative Property)
Depression of Freezing Point ( ΔTf)
.
.
ie ΔTf α molality
ΔTf = Kf x molality,
or cryoscopic constant
Molal depression constant is the
depression in depression in FP when molality is
unity
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Relation between Depression of Freezing Point and molar
mass of the solute
ΔTf = Kf x m ,
WBx 1000
But molality m=-------------
MB X WA
WB x 1000
ΔTf= Kf x --------------
MB x WA
1000 Kf WB
MB = -----------------
ΔTf WA
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4. Osmotic pressure
Osmosis: If a solvent and solution are separated by a semipermeable
membrane ,the solvent molecules will flow through the membrane from
pure solvent to solution. This process of flow of solvent is called osmosis.
The excess pressure required to just prevent osmosis is called osmotic
pressure.
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Molar mass and Osmotic Pressure
π α C α T
nB
π = ---- x RT wB
V But nB = -----
MB
wB x R xT
MB = ---------------
π V
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Isotonic Solutions
Two solutions having same osmotic pressure at a given
temperature are called isotonic solutions.
π1 = π2
w1 w2
------ = --------
M1 M2
Between two solutions one having higher osmotic pressure is called
hypertonic solution and that having lower osmotic pressure is called
hypotonic solution.
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Reverse Osmosis and Water Purification
The direction of osmosis can be reversed if a pressure larger than the
osmotic pressure is applied to the solution side . This phenomenon is
called reverse osmosis.
Reverse osmosis is used in desalination of sea water.
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Abnormal Molar Masses
When we determine the molar mass of certain substances by colligative property methods, it
will be higher or lower than the actual value.This is called abnormal molar mass.
It is due to (i) association or (ii) dissociation
(i) If association take place the molar mass increases.
eg : Acetic acid undergoes dimerization in benzene.So molar mass will be 120 instead of 60.
(ii) If dissociation take place molar mass decreases
eg: KCl in water
KCl ---- K+ + Cl-
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Van’t Hoff factor (i)
Normal molar mass
i= ------------------------------
Abnormal molar mass
Observed colligative property
= -----------------------------------------------
Calculated colligative property
If I = 1 neither association nor dissociation.
If I > 1, dissociation
If I < 1 , association
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Inclusion of van’t Hoff factor modifies the equations
PA0-ps nB
Lowering of VP ---------- = i ----
pA0 nA
Elevation of Boiling point , Δ Tb = i Kb m
Depression of Freezing point Δ Tf = iKf m
i nBRT
Osmotic pressure of solution, π = --------
V
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