Question

For 1 molal aqueous solution of the following compounds ,which one will show the highest
freezing point?
A) \[\left[ {Co{{\left( {{H_2}O} \right)}_4}C{l_2}} \right]Cl.2{H_2}O\]
B) \[\left[ {Co{{\left( {{H_2}O} \right)}_3}C{l_3}} \right].3{H_2}O\]
C) \[\left[ {Co{{\left( {{H_2}O} \right)}_6}} \right]C{l_3}\]
D) \[\left[ {Co{{\left( {{H_2}O} \right)}_5}Cl} \right]C{l_2}.{H_2}O\]

Answer 1

Hint:We should keep in mind that more the depression in freezing point more is the freezing point of the substance.then we need to find the number of ions in order to determine the highest freezing point.

Complete step-by-step answer:
We know that the freezing point is given with the following equation;
\[
 \Delta Tf = ixm \times KF \\
 m = 1 \\
 \Delta Tf = i \times KF \\
\]
Here the depression is at the freezing point. This depression can be in that of a solution and a solute.
Further it is a constant which depends on the properties of a solvent but remember not the solute.
The freezing point depression is equal to the freezing point of the solvent minus the freezing point of the solution.Further it is also directly proportional to the molal concentration of the solute.
Further we can say that the freezing point depression depends on the only and only solvent nor the solute.Now we will talk about the van't hoff factor .In ionic compounds we should know that the van't hoff factor depends on the number of discrete ions in the formula unit of the substance.
Then,we will talk about the number of ions in each option.
Talking about option first \[\left[ {Co{{\left( {{H_2}O} \right)}_4}C{l_2}} \right]Cl.2{H_2}O\]
, the number of ions is equal to two.
Then talking about option second \[\left[ {Co{{\left( {{H_2}O} \right)}_3}C{l_3}} \right].3{H_2}O\]
,the number of ions is equal to one.
Then for third option \[\left[ {Co{{\left( {{H_2}O} \right)}_6}} \right]C{l_3}\]
,the number of ions is equal to four.
Further talking about the last option ,\[\left[ {Co{{\left( {{H_2}O} \right)}_5}Cl} \right]C{l_2}.{H_2}O\]
,the number of ions is equal to two.
So,option B has the highest freezing point.

Note:The compound which has lower number of ions dissolved, lesser the freezing point depression and higher be the freezing point.