Question

Rank these aqueous solutions from highest boiling point to lowest boiling point.

1 = highest boiling point; 4 = lowest boiling point

0.40 m C2H6O2

0.20 m Na3PO4

0.30 m KNO3

0.20 m C6H12O6  

Answer 1

you have to use the equation for boiling point elevation

, i is the vant hoff factor, kb is the ebulloscopic constant , lets suppose that we have the same solvent so we dont need the value of kb , the vant hoff factor is a parameter that tells how many species are in the solute , for organic compounds this value is 1, for ionic compounds it depends on the number of ions dissociated so.

C₂H₆O₂ is etylenglycol which is an organic compound so it has a vant hoff factor equals to 1

0.4 C2H6O2, = 1 * Kb * 0.4 = 0.4 Kb

0.2 Na3PO4, this will dissociate into 3 ions of Na and 1 PO₄^-3 , vant hoff factor is 4

= 4 * kb * 0.2 = 0.8 Kb

0.3 KNO₃, this will dissociate into K⁺ and NO₃ , vant hoff factor is 2

= 0.3*kb*2 = 0.6 Kb

0.2 m of C₆H₁₂O₆, which might be glucose is an organic compound, so vant hoff factor is equal to 1

= 1 * Kb * 0.2 = 0.2 Kb

so if we rank these value on decreasing order

Highest: 0.2 Na3PO4 with = 0.8 Kb

0.3 KNO_{3 with} = 0.6 Kb

0.4 C2H6O2, = 0.4 Kb

Lowest 0.2 m C₆H₁₂O_6, = 0.2 Kb

remember that is Boiling Temp (solution) - Boiling Temp (pure solvent), if is higher then the boiling temperature of the solution will be higher

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