Q.1. The mixture which shows positive deviation from Raoult’s law is : (2020)
(a) Acetone + Chloroform
(b) Chloroethane + Bromoethane
(c) Ethanol + Acetone
(d) Benzene + Toluene
Acetone + ethanol shows positive deviation from Raoult’s law. Pure ethanol possesses H-bonding and adding acetone to ethanol causes breaking of some H-bonds.
This causes increase in observed vapour pressure.
Q.2. The freezing point depression constant (Kf) of benzene is 5.12 K kg mol-1. The freezing point depression for the solution of molality 0.078 m containing a non-electrolyte solute in benzene is (rounded off upto two decimal places) : (2020)
(a) 0.40 K
(b) 0.60 K
(c) 0.20 K
(d) 0.80 K
ΔTf = ikfm
⇒ ΔTf = 1 × 5.12 × 0.078
ΔTf = 0.3993
ΔTf = 0.40 K
Q.3. For an ideal solution, the correct option is : (2019)
A: Δmix S = 0 at constant T and P
B: Δmix V ≠ 0 at constant T and P
C: Δmix H = 0 at constant T and P
D: Δmix G = 0 at constant T and P
For ideal solution,
Δmix H = 0
Δmix S > 0
Δmix G < 0
Δmix V = 0
Q.4. The mixture that forms maximum boiling azeotrope is: (2019)
A: Water + Nitric acid
B: Ethanol + Water
C: Acetone + Carbon disulphide
D: Heptane + Octane
Solutions showing negative deviation from Raoult's law form maximum boiling azeotrope. Water and Nitric acid → forms maximum boiling azeotrope.
Q.5. If molality of the dilute solutions is doubled, the value of molal depression constant (Kf) will be :- (2017)
Kf does not depend on concentration of solution. It only depends on nature of solvent so it will be unchanged.
Q.6. Which of the following is dependent on temperature? (2017)
B: Mole fraction
C: Weight percentage
Temperature dependent unit is molarity.
Q.7. At 100°C the vapour pressure of a solution of 6.5 g of a solute in 100 g water is 732 mm. If Kb = 0.52, the boiling point of this solution will be : (2016)
Q.8. Which of the following statements about the composition of the vapour over an ideal 1 : 1 molar mixture of benzene and toluene is correct ?
Assume that the temperature is constant at 25°C. (Given Vapour Pressure Data at 25ºC, Benzene = 12.8kPa, toluene = 3.85kPa) (2016)
A: Not enough information is given to make a prediction.
B: The vapour will contain a higher percentage of benzene.
C: The vapour will contain a higher percentage of toluene.The vapour will contain a higher percentage of toluene.
D: The vapour will contain equal amounts of benzene and toluene.
Due to high partial vapour pressure of Benzene as compare to that of toluene so the mole fraction of Benzene will be higher than that of toluene. As a result the vapour will contain a higher percentage of Benzene.
Q.9. Which one is not equal to zero for an ideal solution ? (2015)
A: ΔP = Pobserved - PRaoult
B: Δ Hmix
D: Δ Vmix
For ideal solution, ΔSmix = 0.
Q.10. The boiling point of 0.2 mol kg-1 solution of X in water is greater than equimolal solution of Y in water. Which one of the following statements is true in this case ? (2015)
A: Y is undergoing dissociation in water while X under goes no change
B: X is undergoing dissociation in water
C: Molecular mass of X is greater than the molecular mass of Y.
D: Molecular mass of X is less than the molecular mass of Y.
Molality of solution of x = molality of solution of y = 0.2 mol/kg
By elevation in boiling point relation
Q.11. Which one of the following electrolytes has the same value of van‘t Hoff‘s factor (i) as that of Al2(SO4)3 (if all are 100% ionised) (2015)
Q.12. Of the following 0.10 m aqueous solutions, which one will exhibit the largest freezing point depression? (2014)
A: Al2 (SO4 )3