Equal amounts in grams of following sub-stances were dissolved in equal amount of water. Which of these will have the highest boiling point ?

Options

A. Urea `(NH_(2) CONH_(2))`
B. Glucose `(C_(6)H_(12)O_(6))`
C. Sodium chloride ( NaCl )
D. Calcium chloride `(CaCl_(2))`

Answer

C

Explanation

The simple inspection of the question shows that (C) should be the correct choice because `CaCl_(2)` will give 3 mol of ions for 1 mol of `CaCl_(2)` dissolved (assuming it to be completely dissociated). However, in the given question, the amounts are given in grams. If we assume, `w` gram of all the substances are dissolved in 1000 g of solvent, then
Molal conc. of NaCl `=(w)/(58.5)m`
Molar conc. of `CaCl_(2)=(w)/(111)` m
Since NaCl gives two mole of ions for one mole of it so that
Molar concentration of ions in solution
`=(w)/(58.5)xx2=0.034w`
`CaCl_(2)` gives three moles of ions for 1 mol of it so that
Molar conc. of ions in solution
`=(w)/(111)xx3=0.027 w`
Therefore, molal conc. of solute in NaCl solution is more than in `CaCl_(2)` solution.