Q. 28

(a) Differentiate

Answer :

(a) Molarity: It is the number of moles of solute dissolved in 1 litre of the solution. It is temperature dependent.
M=

Molality: It is the number of moles of solute dissolved in 1 kg of the solvent. It is temperature independent.
m=


Molality is independent of temperature, whereas molarity is a function of temperature because volume depends on temperature and mass does not.


(b) Given: w= 10.50 g


W= 200 g


= 184 g


Kƒ = 1.86 K kgmol-1


MgBr2 dissociates as per the given equation:


MgBr2 Mg2+ + 2Br-


So, total no. of moles after dissociation = 1+2 = 3


Thus, i = = 3


Using the formula


Tƒ = i×Kƒ×m


T0f–Tf =


0-Tf =


-Tf = = 1.592


Tf = -1.592


Or Tf = -271.56 K


OR


(a) Osmosis: Osmosis is the phenomenon of flow of solvent through a semi-permeable membrane from the region of higher concentration to the region of lower concentration.



Osmotic Pressure: The osmotic pressure of a solution is the excess pressure that must be applied to the solution to prevent the passage of solvent molecule through a semi-permeable membrane into the solution.



Yes, osmotic pressure is a colligative property as it depends only on the amount of solute present in the solution.


(b) Given: w= 15 g


W= 250g


= 58.44 g


Kb = 0.512 K kgmol-1


NaCldissociates as per the given equation:


NaCl Na+ + Cl-


So, total no. of moles after dissociation = 1+1 = 2


Thus, i = = 2


Using the formula


Tb = i×Kb×m


Tb – T0b=


Tb –373=


Tb= = 1.05 + 373


Tb = 374.05 K


or Tb = 101.05


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