Question

Which of the following aqueous solutions should have the lowest boiling point?

0.50 m KCl

2.0 m C₆H₁₂O₆

0., 50 m CaBr₂

1.5 m KI

0.50 m Na₂SO₄

Answer 1

answer :   0.50 m KCl

Explanation :

we know the relation between elevation in boiling point , vanthoff factor (i) , molality (m)

Tb = Kb x ( i x m)

Tb-To = Kb x ( i x m)

Tb = Kb x ( i x m) +To

boiling point of solution increase with increase in van'thoff factor(i) and molality (m)

0.50 m KCl    , i value = 2 ,     concentration x van't hoff factot = 2 x 0.5 = 1

2.0 m C6H12O6   ,   i value = 1    ,   concentration x van't hoff factot= 2

0., 50 m CaBr2    , i value = 3   ,     concentration x van't hoff factot= 3 x 0.5 = 1.5

1.5 m KI               , i value = 2 ,    concentration x van't hoff factot = 2 x 1.5 = 3.0

0.50 m Na2SO4,   i value = 3   ,      concentration x van't hoff factot= 3 x 0.5 = 1.5

so lowest (i x m) value for 0.5 m KCl it has lowest boiling point.

highest for 1.5m KI

order : 1.5m KI > 2.0 m C6H12O6   > 0.50 m Na2SO4 =0.50 m CaBr2 > 0.50 m KCl