(a) Differentiate between molality and molarity of a solution. How does a change in temperature influence their values?
(b) Calculate the freezing point of an aqueous solution containing 10.50 g of MgBr₂ in 200 g of water. (Molar mass of MgBr₂ = 184 g) (K_ƒ for water = 1.86 K kgmol^-1

OR

(a) Define the terms osmosis and osmotic pressure. Is the osmotic pressure of a solution a colligative property? Explain
(b) Calculate the boiling point of a solution prepared by adding 15.00 g of NaCl to 250.0 g of water. (K_b for water = 0.512 K kg mol^-1, Molar mass of NaCl = 58.44 g)

(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

K_ƒ = 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

∆ T_ƒ = i×K_ƒ×m

T⁰_f–T_f =

0-T_f =

-T_f = = 1.592℃

∴T_f = -1.592℃

Or T_f = -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

K_b = 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

∆ T_b = i×K_b×m

T_b – T⁰_b=

T_b –373=

T_b= = 1.05 + 373

∴ T_b = 374.05 K

or T_b = 101.05℃