Solution
KEY CONCEPTS
Solution is the homogeneous mixture of two or more substances in which the components are uniformly
distributed into each other. The substances which make the solution are called components. Most of the
solutions are binary i.e., consists of two components out of which one is solute and other is solvent.
Ternary solution consists of three components
Solute ‐ The component of solution which is present in smaller quantity.
Solvent – The component of solution present in larger quantity or whose physical state is same as the
physical state of resulting solution.
Types of solutions: Based on physical state of components solutions can be divided into 9 types.
Solubility ‐ The amount of solute which can be dissolved in 100grm of solvent at particular temp. to
make saturated solution.
Solid solutions are of 2 types ‐
1. Substitutional solid solution e.g. Brass (Components have almost similar size)
2. Interstitial solid solution e.g. steel (smaller component occupies the interstitial voids)
Expression of concentration of solution
1. Mass percentage= amount of solute present in 100grm solution.
Percentage =
For liquid solutions percentage by volume is expressed as =
2. Mole fraction it is the ratio of no. of one component to the total no. of moles of all components. It is
expressed as ‘x’. For two component system made of A and B ,XA= nA +nB , XB= nA+nB , Sum of all the
components is 1 ; XA+XB =1
3. Molarity (M) =
It decreases with increase in temperature as volume of solution increases with temperature.
4. Molality (m) =
No effect of change of temperature on molality as it is mass to mass ratio.
5. Normality (N) =
It changes with changes temperature.
6. Parts per million (ppm) concentration of very dilute solution is expressed in ppm.
Ppm =
Vapor pressure – It is defined as the pressure exerted by the vapour of liquid over the liquid over the
liquid in equilibrium with liquid at particular temperature vapour pressure of liquid depends upon
nature of liquid and temperature.
Roult’s Law –
1. For the solution containing non‐volatile solute the vapor pressure of the solution is directly
proportional to the mole fraction of solvent at particular temperature
PA XA
PA = P0
A.XA
2. For the solution consisting of two miscible and volatile liquids the partial vapor pressure of
each component is directly proportional to its own mole fraction in the solution at particular
temperature.
PA=P0
A. XA, PB=P0
B .XB
And total vapor pressure is equal to sum of partial pressure. Ptotal = PA + PB
Ideal solution – The solution which obeys Roult’s law under all conditions of temperature and
concentration and during the preparation of which there is no change in enthalpy and volume on mixing
the component.
Conditions –
PA = P0
A XA, PB = P0
B.XB
Mix = 0, mix = 0
This is only possible if A‐B interaction is same as A‐A and B‐B interaction nearly ideal solution are –
1. Benzene and Toluene
2. Chlorobenzene and Bromobenzene
Very dilute solutions exhibit ideal behavior to greater extent.
Non‐ideal solution –
(a) PA ≠ P0
A.XA (b) PB ≠P0
B.XB
(b) mix ≠ 0 (d) mix ≠ 0
For non‐ideal solution the A‐B interaction is different from A‐A and B‐B interactions
i. For solution showing positive deviation
PA > P0
A, PB > P0
B. XB
Mix = positive, mix=positive (A‐B interaction is weaker than A‐A and B‐B )
E.g. alcohol and water
ii. For the solution showing negative deviation
PA < P0
A.XA, PB<P0
B.XB
Mix= negative, mix = negative’
A‐B interaction is stronger than A‐A and B‐B interactions
E.g. Chloroform, acetone, HCl and water
What is Azeotrope? – The mixture of liquids at particular composition which has constant boiling point
which behaves like a pure liquid and cannot be separated by simple distillation. Azeotropes are of two
types:
(a) minimum boiling Azeotrope (mixture which shows +ve deviations ) ex. alcohol and water
(b) maximum boiling Azeotrope (which shows –ve deviations) ex. acetone and chloroform
Colligative Properties ‐ Properties of ideal solution which depends upon no. of particles of solute but
independent of the nature of particle are called colligative property
Relative lowering in vapour pressure:
(Po
A – PA )/ Po
A = XB
Determination of molar mass of solute
MB =( WA× MA× Po
A)/WA×(Po
A –PA)
Elevator in Boiling Point
ΔTB = Kb. m
Where ΔT B = T’
B‐ To
B
Kb = molal elevator constant
M = molality
MB =(Kb×1000×WB)/ΔTB×WA
Depression in Freezing Point:
ΔTf = kf. m
Where ΔTf – T’f ; m = molality
Kf = molal depression constant
unit = k.kgmol‐1
Osmotic Pressure
The hydrostatic pressure which is developed on solution side due movement of solvent particles from
lower concentration to higher concentration through semipermeable membrane denoted as π and it is
expressed as
Π = n RT
V
Π = CRT
n = No. of moles; v = volume of solution (L)
R = 0.0821 Latmmol‐1; T = temperature in kelvin.
Isotonic solutions have same osmotic pressure and same concentration.
Hypertonic solutions have higher osmotic pressure and hypotonic solutions have lower osmotic
pressure.
0.91% solutions have sodium chloride solution RBC swells up or burst.
Q1‐ What do you mean by Henry’s Law? The Henry’s Law constant for oxygen dissolved in water is
4.34×104 atm at 25o C. If the partial pressure of oxygen in air is 0.2 atm, under atmospheric pressure
conditions. Calculate the concentration in moles per Litre of dissolved oxygen in water in equilibrium
with water air at 25o C.
Ans: Partial pressure of the gas is directly proportional to its mole fraction in solution at particular
temperature.
PA α XA ; KH = Henry’s Law of constant
PA = KH ×A
KH = 4.34×104 atm
PO2 = 0.2 atm
Xo2 = PO2 / KH =0.2 / 4.34×104= 4.6×10‐6
If we assume 1L solution = 1L water
n water = 1000/18 = 55.5
XO2 = nO2 /(nO2+ n H2O ) ~ = nO2 /nH2O
nO2 = 4.6 X 10‐6 X 55.5 = 2.55 X 10‐4 mol
M = 2.55 X 10‐4 M
Q.2. What is Vant Hoff factor?
Ans. It is the ratio of normal molecular mass to observed molecular mass . H is denoted as ‘i’
i = normal m.m / observed m.m
= no. of particles after association or dissociation / no. of particles before
Q.3. What is the Vant Hoff factor in K4[Fe(CN)6] and BaCl2 ?
Ans 5 and 3
Q.4. Why the molecular mass becomes abnormal?
Ans. Due to association or dissociation of solute in given solvent .
Q.5. Define molarity, how it is related with normality ?
Ans. N = M x Basicity or acidity.
Q.6. How molarity is related with percentage and density of solution ?
Ans. M = P x d x10/M.M
Q.7. What role does the molecular interaction play in the solution of alcohol and water?
Ans. Positive deviation from ideal behavior .
Q.8. What is Vant Hoff factor , how is it related with
a. degree of dissociation b. degree of association
Ans. a. α=i – 1/n‐1 b. α = i ‐1 / 1/n ‐1
Q.9. Why NaCl is used to clear snow from roads ?
Ans. It lowers f.p of water
Q10. why the boiling point of solution is higher than oure liquid
Ans. Due to lowering in v.p
HOTS
Q1. Out of 1M and 1m aqueous solution which is more concentrated
Ans. 1M as density of water is 1gm/Ml
Q2. Henry law constant for two gases are 21.5 and 49.5 atm ,which gas is more soluble .
Ans. KH is inversely proportional to solubility .
Q.3. Define azeotrope , give an example of maximum boiling azeotrope.
Q.4. Calculate the volume of 75% of H2SO4 by weight (d=1.8 gm/ml) required to prepare 1L of 0.2M
solution
Hint: M1 = P x d x 10 /98
M1 V1 = M2V2
14.5ml
Q.5. Why water cannot be completely separated from aqueous solution of ethyl alcohol?
Ans. Due to formation of Azeotrope at (95.4%)
SHORT ANSWERS (2 MARKS)
Q.1. How many grams of KCl should be added to 1kg of water to lower its freezing point to ‐8.00C (kf =
1.86 K kg /mol)
Ans. Since KCl dissociate in water completely L=2
; m =
m= 8 / 2X1.86 = 2.15mol/kg.
Grams of KCl= 2.15 X 74.5 = 160.2 g/kg.
Q.2. With the help of diagram: show the elevator in boiling point colligative properties ?
Q.3. what do you mean by colligative properties, which colligative property is used to determine m.m of
polymer and why?
Q.4. Define reverse osmosis, write its one use.
Ans. Desalination of water.
Q.5. Why does an azeotropic mixture distills without any change in composition.
Hint: It has same composition of components in liquid and vapour phase.
Q.6. Under what condition Vant Hoff’s factor is
a. equal to 1 b. less than 1 c. more than 1
Q.7. If the density of some lake water is 1.25 gm /ml and contains 92gm of Na+ ions per kg of water.
Calculate the molality of Na+ ion in the lake .
Ans. n = 92/23 = 4
m= 4/1 = 4m
Q.8. An aqueous solution of 2% non‐volatile exerts a pressure of 1.004 Bar at the normal boiling point of
the solvent . What is the molar mass of the solute .
Hint: P0
A – PA/P0
A = wB X mA / mB X wA
1.013 – 1.004 / 1.013 = 2X 18 /mB X 98
mB = 41.35gm/mol
Q.9. Why is it advised to add ethylene glycol to water in a car radiator in hill station?
Hint: Anti‐ freeze.
Q.10. what do you mean by hypertonic solution, what happens when RBC is kept in 0.91% solution of
sodium chloride?
Q 11. (a). define the following terms.
1. Mole fraction
2. Ideal solutions
(b)15 g of an unknown molecular material is dissolved in 450 g of water. The resulting solution
frrezez at ‐0.34 0c . what is the molar mass of material? Kf for water= 1.86 K Kg mol‐1 .
Ans. 182.35 glmol
Q 12.(a) explain the following :
1. Henry’s law about dissolution of a gas in a liquid .
2. Boling point elevation constant for a solvent
(b)a solution of glycerol (C3h803) in water was prepared by dissolving some glycerol in in 500 g of water.
The solution has a boiling point of 100.42 0c . what mass of glycerol was dissolved to make this solution?
Kb for water = 0.512 k Kg mol‐1
(hint: atb = b*wb*1000
Mb*Wa
Ans. 37.73 gm
Q 13. 2 g of benzoic acid (c6h5cooh) dissolved in 25 g of benzene shows a depression in freezing point
equal to 1.62 K . KF for benzene is 4.9 K Kg mol‐1. What is the percentage association of acid if it forms
dimer in solution. Ans. 99.2%
Q14. Osmotic pressure of a 0.0103 molar solution of an electrolite is found to be 0.70 atm at 270c .
calculate Vant Hoff factor.( R=0.082 L atom mol‐1 K‐1) Ans. 2.76
