Raoult’s law woorksheet

Raoult’s law was discovered by Fransois-Marie Raoult in 1882.

This law states that, ” The vapour pressure of an ideal solution is dependent on the vapour pressure of each chemical component and the mole fraction of the component present in the solution.”

In this article you can find some questions related of Raoult’s law & Vapour pressure , with their answers:


1. The lowering of vapour pressure of the solvent takes place:

(a)    only when the solute is a non-electrolyte

(b)   only when the solute is volatile

(c)    only when the solute is non-volatile

(d)   in all the above three cases


2. When attraction between A – B is more than that between A – A and B – B the solution will show…………… deviation from Raoult’s law:

(a)    Positive

(b)   Negative

(c)    No

(d)    cannot be predicted


3. Which of the following is correct for a solution showing positive deviation from Raoult’s law?

(a)    \Delta V = + ve, \Delta H = + ve

(b)   \Delta V = - ve, \Delta H = + ve

(c)    \Delta V = + ve, \Delta H = - ve

(d)   \Delta V = - ve, \Delta H = - ve


4. Which pair out of the following will not form an ideal solution?

(a)    C_2H_5Br + C_2H_5I

(b)   H_2O + C_4H_9OH

(c)    CCl_4 + SiCl_4

(d)   C_6H_{14} + C_7H_{16}


5. The vapour pressure of pure benzene and toluene are 160 and 60 torr respectively. The mole fraction of toluene in vapour phase in contact with equimolar solution of benzene and toluene is:

(a)    0.6

(b)   0.50

(c)    0.27

(d)   0.74


6. The vapour pressure of a solvent A is 0.80 atm. When a non-volatile substance B is added to this solvent its vapour pressure drops to 0.6 atm. The mole fraction of B in the solution is:

(a)    0.25

(b)   0.90

(c)    0.50

(d)   5.0


7. At room temperature, the mole fraction of a solute is 0.25 and the vapour pressure of a solvent is 0.80 atm. Then the lowering of vapour pressure is:

(a)    0.60

(b)   0.75

(c)    0.20

(d)   0.80


8. A binary liquid (AB) shows positive deviation form Raoult’s law when:

(a)    P_A > P^0_A X^{liq}_A \text{and} P_B > P^0_B X_B^{liq}

(b)   Intermolecular forces A – A, B – B > A – B

(c)    \Delta_{mix} > = 0

(d)   \Delta_{mix} > 0

(e)   (a), (b), (c)


9. The azeotropic solutions of two miscible liquids:

(a)    can be separated by simple distillation

(b)   may show positive or negative deviation from Raoult’s law

(c)    are supersaturated

(d)   none of these


10. Identify the mixture that shows positive deviation form Ra0ult’s law:

(a)    CHCl_3 + (CH_3)_2CO

(b)   (CH_3)_2 CO + C_6H_5NH_2

(c)    CHCl_3 +C_6H_6

(d)   (CH_3)_2 CO +CS_2



1.(d)     2. (b)    3. (a)       4. (b)     5. (c)

6. (a)     7. (c)     8. (e)     9. (b)     10. (d)

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