Question

Explaining why, which, if any, of the following water solutions will have the lowest freezing temperature ? Explain the reason for your answer. A. 0.20m NaCl B. 0.10m AlCl3 C. 0.40m KBr D. 0.20m CaCl2

Answer 1

More the number ions produced on dissociation will have higher the depression in freezing point

Depression in freezing point() directly proporional to number of ions (i) along with molality of the solution

Let us find which has high molality of ions

A) NaCl(aq) ---> Na⁺(aq) + Cl^-(aq)

Complete dissociation of 0.2m NaCl gives 0.2 m Na⁺ and 0.2 m Cl^- ions

Total molality of ions = 0.2m Na⁺ + 0.2m Cl^- ions = 0.4 m ions

B) 0.10m AlCl₃

AlCl₃(aq) ---> Al³⁺(aq) + 3Cl^-(aq)

Total molality of ions = 0.1m Al³⁺+ 3( 0.1 ) m Cl^-ions = 0.4 m ions

C) 0.40m KBr

KBr(aq) ---> K⁺(aq) + Br^-(aq)

Total molality of ions = 0.4 m Na⁺ + 0.4 m Cl^- ions = 0.8 m ions

D) 0.20m CaCl₂

CaCl₂(aq) ---> Ca²⁺(aq) + 2Cl^-(aq)

Total molality of ions = 0.2 m Ca²⁺ + 2(0.2 m) Cl^- = 0.6 m ions

​Answer is C) KBr is giving high molality of ions so it will have highest depression in freeziing point.