Question

Put these in order of lowest freezing point to highest freezing point at standard pressure.

N2

1m HCOOH(aq)

1m KCl(aq)

CH2Cl2

1m SrI2(aq)

CH3OH

H2O

1m Fe2(SO4)3(aq)

Br2

Answer 1

Among thepure components , molecular weight plays important role in deciding the freezing point.

Thus N2 with lowest molar mass and only vanderwaals' attractions has the lowest freezing point.

Ch3OH with next lower molar mass has the next lower freezing point .

and Br2 with highest molar mass has the highest of these.

Thus the order of pure components is

N2 < CH3OH < CH2CL2 < Br2 (increasing molar mass increasing freeezing point)

Next are solutions and water.

From the colligative property of DEPRESSION IN FREEZING POINT, more the number of solute particles in the solution, lower is the freezing point.

Thus water is the highest boiling of all these (pure solvent).

among the solutions the F.P. order is

1mFe2(SO4)3 < 1m SrI2 < 1m KCl < 1m HCOOH < H2O

number of particles 5 in Fe2(SO4)3 , 3 in SrI2 , 2 in KCL and HCOOH.

However HCOOH is a weak electrolyte and KCl is trong. Thus HCOOH produces less number of ions due to lower degree of dissociation.

Thus the overall order of F.P. is

N2 < CH3OH < CH2CL2 < Br2 < 1mFe2(SO4)3 < 1m SrI2 < 1m KCl < 1m HCOOH < H2O