Abnormal Coll...

Abnormal Colligative Properties

Trending Questions

When benzoic acid dissolve in benzene, the observed molecular mass is:

Q. The boiling point of a solution containing 0.61 g of benzoic acid in 50 g of carbon disulphide assuming

84 %

dimerization of the acid, where boiling point and Kb of

C S_{2}

being

{46.2}^{\circ} C

and

2.3 K k g m o l^{- 1}

is :

${46.3444}^{\circ} C$
${46.3434}^{\circ} C$
${46.3334}^{\circ} C$
${46.3344}^{\circ} C$

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The observed osmotic pressure of a solution of benzoic acid in benzene is less than its expected value because

Benzene is a non-polar solvent
Benzoic acid molecules are associated in benzene
Benzoic acid molecules are dissociated in benzene
Benzoic acid is an organic compound

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Q. At same temperature which pair of the following solutions are isotonic? (if all are 100% ionised)

$0.2 M B a C l_{2}$ and $0.2 M U r e a$
$0.1 M U r e a$ and $0.1 M N a C l$
$0.1 M N a C l$ and $0.1 M K_{2} S O_{4}$
$0.1 M B a (N O_{3})_{2}$ and $0.1 M N a_{2} S O_{4}$

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Q. The freezing point

(i n^{\circ} C)

of solution containing 0.1 g of

K_{3} [F e (C N)]_{6}

(mol.wt.392) in 100 g of water(

K_{f}

=1.86K kg

m o l^{- 1}

) is

$- 2.3 \times 10^{- 2}$
$- 5.7 \times 10^{- 2}$
$- 5.7 \times 10^{- 3}$
$- 1.2 \times 10^{- 2}$

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Q. The elevation of boiling point of

0.10 m

aqueous

C r C 1_{3} . x N H_{3}

solution is two times that of

0.05 m

aqueous

C a C l_{2},

solution. The value of

x

is [Assume

100 %

ionisation of the complex and

C a C l_{2}

, coordination number of

C r i s 6

, and that all

N H_{3}

molecules are present inside the coordination sphere]
(JEE MAIN 2020)

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Q. Pure water freezes at 273 K and 1 bar. The addition of 34.5g of ethanol to 500g of water changes the freezing point of the solution. Use the freezing point depression constant of water as 2K kg

m o l^{- 1}

. The figures shown below represent plots of vapour pressure (V.P.) versus temperature (T). [Molecular weight of ethanol is 46g

m o l^{- 1}

]
Among the following, the option representing change in the freezing point is

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Q. The freezing point depression of a 0.10 m solution of HF(aq) solution is

- {0.201}^{\circ} C

. Calculate the percent dissociation of HF(aq).

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Q. A decimolar solution of potassium ferrocynide is

50 %

dissociated at 300 K. Given

S = 8.314 J K^{- 1} m o l^{- 1}

. The osmotic pressure of the solution is :

$7.438 \times 105 N m^{- 2}$
$7.834 \times 105 N m^{- 2}$
$7.348 \times 105 N m^{- 2}$
$7.483 \times 105 N m^{- 2}$

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Q. The density of a 0.438 M solution of potassium chromate at 298 K is

1.063 g c m^{- 3}

. Calculate the vapour pressure of water above this solution. Given :

P^{0}

(water) = 23.79 mm Hg.

23.22
43.23
54.2
12.1

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Q. A compound X undergoes tetramerisation in a given organic solvent. The van ’t Hoff factor ‘i’ is calculated as 0.05y. Find y. (Assuming 100% association)

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Q. 2.5 g of a monobasic acid when dissolved in 100 g of water elevates the boiling point of the solution by

{0.256}^{\circ} C

. If 0.5 g of the acid requires 8 milliequivalents of NaOH for complete neutralisation, then the degree of dissociation of the acid is: [

K_{b}

of water

= 0.512 K k g m o l^{- 1}

]

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Q. The experimental values of colligative properties of many solutes in solution resembles calculated values of colligative properties.
However in some cases, the experimental values of colligative properties differ widely than those obtained by calculations. Such experimental values of colligative properties are known as abnormal values of colligative properties. The causes for abnormal values of colligative properties are:
(i) Dissociation of solute: It increases the colligative properties.
e.g.: Dissociation of

KCl, NaCl

etc. in

H_{2} O

.
(ii) Association of solute: It decreases the colligative properties.
e.g.: Dimerisation of acetic acid in benzene.

If the degree of dissociation of an electrolyte

A_{2} B_{3}

is 25% in a solvent, then:

Normal boiling point = Experimental boiling point
Normal freezing point > Experimental freezing point
Normal osmotic pressure $= \frac{1}{2}$ Experimental osmotic pressure
Normal molecular weight $= \frac{1}{4}$ Experimental molecular weight

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