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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