Question

(d) Why boiling point of 0.1 M CaCl2,(aq) is more than
0.1 M NaCl(aq)?
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Answer 1

Explanation:

Boiling point is a colligative property of solution, therefore change in boiling point is in direct proportion to number of particles ( or number of moles). Now since solvent isn't mentioned therefore we will be assuming that both the solutions were prepared in same solvent. In order to understand the further concept regarding change in boling point of a solution one should be aware of the fact that

∆T (change in boiling point) = i x Kb x m

where Kb = ebulioscopic constant

m = molality of the solution

i = van't Hoff factor

In 1M solution of NaCl i = 2 because after adding NaCl it get dissociated ( i.e. on adding 1 mole of NaCl in the solution we obtain 2 mole of ions )

And In 1M solution of CaCl2 i = 3

Now one should also know that Kb depends on the solvent.

Therefore ∆T (NaCl) = 2 Kbm

And ∆T (CaCl2) = 3kbm

From above two expressions we easily conclude that 1M solution of CaCl2 has higher boiling point than 1M solution of NaCl.

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