2.7 kg of each of water and acetic acid are mixed. The freezing point of the solution will be -x C. Consider the acetic acid does not dimerise in water, nor dissociates in water. x = (nearest integer) [Given: Molar mass of water = 18 g mol-1, acetic acid = 60 g mol-1 Kf H2O : 1.86 K kg mol-1 Kf acetic acid: 3.90 K kg mol-1 freezing point: H2O = 273 K, acetic acid = 290 K]
Answer
31
Solution
Moles of water = 270018 = 150
Moles of acetic acid = 270060 = 45
∵ water is in larger amount ⇒ water is the solvent, acetic acid the solute
m = 452.7 = 16.67 mol kg-1
Tf = Kf m = 1.86 16.67 = 31 K
⇒ f.p. = 0 − 31 = −31 °C ∴ x = 31
Answer: 31