Answer to Question #59932 in Inorganic Chemistry for Anushree Paul

Question

how we can understand that which one of the following aqueous solution has highest freezing point?
a. 0.1M Nacl
b. 0.1M BaCl2
c. 0.1M Al2(SO4)3
d. 0.1M urea

Answer 1

A solution will solidify (freeze) at a lower temperature than the pure solvent. This is the colligative property called freezing point depression.
The more solute dissolved, the greater the effect. An equation has been developed for this behavior. It is: ΔT = i *Kf *m
The Van 't Hoff factor is symbolized by the lower-case letter i. It is a unitless constant directly associated with the degree of dissociation of the solute in the solvent.
Substances which do not ionize in solution, like urea, have i = 1.
Substances which ionize into two ions, like NaCl, have i = 2.
Substances which ionize into three ions, like BaCl2, have i = 3.
The substance like Al2(SO4)3 has i= 5.
Answer : Al2(SO4)3 has the highest freezing point (has the lowest temperature), then BaCl2 comes, NaCl and the urea is last.