(a) A 5% solution (by mass) of cane sugar in water has a freezing point of 271 K. Calculate the freezing point of 5% solution (by mass) of glucose in water. The freezing point of pure water is 273.15 K.

(b) Why is osmotic pressure of 1 M KCl higher than 1 M urea solution?

(c) What type of liquids form ideal solutions?

OR

(a) 1.0 g of a non-electrolyte solute dissolved in 50 g of benzene lowered the freezing point of benzene by 0.40 K. The freezing point depression constant of benzene is 5.12 K kg/mol. Find the molar mass of the solute.

(b) What is the significance of Henry’s law constant, K_H?

(c) What leads to anoxia?

(a) Molar mass of cane sugar C₁₂H₂₂O₁₁ = 342 g/mol

5% solution (by mass) of cane sugar in water means 5g of cane sugan is in 95g of water i.e 0.095kg of water.

No. of moles of cane sugar = = 0.0146 mol

Molality of sugar =

m = = 0.153 m

ΔT_f of cane sugar = 273.15 – 271 = 2.15 K

ΔT_f = K_f

K_f = = = 14.05 K kg/mol

Molar mass of glucose = 180 g/mol

5% solution (by mass) of glucose in water means 5g of cane sugan is in 95g of water i.e 0.095kg of water

No. of moles of glucose = = 0.027 mol

Molality of glucose = = 0.284 m

Now, ΔT_f = K_f

= 14.05 0.284

= 3.99 K

Hence, the freezing point of glucose in water is (273.15 – 4)K = 269.15 K.

(b) Osmotic pressure of 1 M KCl is higher than 1 M urea solution. Osmotic pressure is a colligatve property, it depends on no. of solute particles. So, KCl will ionize into K⁺ and Cl^- whereas urea does not ionize at all. Thus, osmotic pressure of 1 M KCl is higher than 1 M urea solution.

(c) The liquids which form ideal solutions have solute- solute and solvent- solvent interactions nearly equal to those between solute- solvent. Example is solution of n-hexane.

OR

(a) Given, Mass of solvent (w₁) = 50 g

Mass of solute (w₂) = 1 g

Molar mass of solute (M₂) = ?

K_f = 5.12 K kg mol^-1

T_f = 0.40 K

ΔT_f =

M₂ = = 256 g/mol

(b) Significance of Henry’s law constant is that higher the value of K_H at a given pressure, lower is the solubility of gas in the liquid. This property is utilized in many applications.

(c) At high altitudes, the partial pressure of oxygen is less than that at ground level. This leads to low concentration of oxygen in blood and this is called anoxia.