In: Chemistry
Which aqueous solution will have the lowest freezing point? (Hint: Relate to colligative properties.)
0.140 molal MgCl2 |
||
0.75 molal LiCl |
||
0.150 molal KBr(aq) |
||
0.100 molal NaBr(aq) |
MgCl2 is a strong electrolyte.
Number of particles due to MgCl2 in aqueous solution = 3 (1 Mg2+ and 2 Cl-)
Therefore, the effective molality of the aqueous solution of 0.140 molal MgCl2 =0.140 m x 3 = 0.420 m
LiCl is a strong electrolyte.
Number of particles due to LiCl in aqueous solution = 2 (1 Li+ and 1 Cl-)
Therefore, the effective molality of the aqueous solution of 0.75 molal LiCl =0.75 m x 2 = 1.50 m
KBr is a strong electrolyte.
Number of particles due to KBr in aqueous solution = 2 (1 K+ and 1 Br-)
Therefore, the effective molality of the aqueous solution of 0.150 molal KBr = 0.150 m x 2 = 0.300 m
NaBr is a strong electrolyte.
Number of particles due to NaBr in aqueous solution = 2 (1 Na+ and 1 Br-)
Therefore, the effective molality of the aqueous solution of 0.100 molal NaBr = 0.100 m x 2 = 0.200 m
Now, the freezing point depression of the aqueous solution is proportional to the effective molality of the solution.
Hence, the aqueous solution that will have the lowest freezing point = 0.75 molal LiCl