Question

A chemist dissolves 1 mol nacl in a 2.0-kg sample of water, then dissolves 1 mol sucrose in another 2.0-kg sample of water. why does the nacl solution have the lower freezing point?

Answer 1

Due to more number of solute particles in NaCl, it will have lower freezing point.

Step-by-step explanation:

Lowering in freezing point is a colligative property. It depends upon the number of solute particles.

Now when we dissolve NaCl and sucrose in equal moles in two same mass of samples of water, the number of particles in NaCl solution is more as compared to sucrose.

NaCl being an electrolyte will dissociate into its ions (Na⁺ and Cl⁻). Thus each mole of NaCl will give more than one mole of solute particles.

Sucrose being a non electrolyte, will not dissociate and thus its one mole will give only one mole of solute particles.

Depression in freezing point of NaCl will be thus more than that of sucrose solution.

Answer 2

NaCl will have a lower freezing point because more particles interferes with the freezing process than sucrose. When 1 mole of NaCl is in solution, it dissociates into ions the Na+ and Cl- ions. So, there will be times 2 particles that will interact. However, for sucrose it does not dissociates into ions, it stays as a molecule so there are less particles that would hinder the process.