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Short Answer Type

51. Define Raoult’s law?

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52. Why is the osmotic pressure measurement preferred for determining molecular mass of proteins?

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53. Why does the boiling point of a solvent increase by the presence of a solute in it?

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54. A deci-molar solution of K₄ [Fe(CN)₆] is 50% dissociated at 300 K. Calculate the osmotic pressure of solution (R = 0.082)/L atm K^–1)?

Answer:
The given complex is ionsiable and it dissociates as follow

K_{4} [Fe (CN)_{6}] \to 4 K^{+} + [Fe (CN)_{6}]^{4 -}

(1-a) 4a a

Where a is the degree of dissociation of a complex.
intial moles of complex =1
moles after dissociation of the complex = 1-a + 4a+a = 1+4a

since osmotic pressure is directly proportional to the number of moles, hence

P_observe/ P_normal= (1+4a)/1

Dissociation takes place only 50% a= 0.50
P/2.462 = 1+(4 x 0.50)
p/2.462 = 1+2
p/2.462=3
p= 2.462x 3
p=7.386 atm

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