Question

Which of the following liquids will have the lowest freezing point/ A) pure h20 B)aqueous KF(0.50 m) C)aqueous sucrose (0.60 m) D)aqueous glucose (0.60 m) E) aqueous Fel3 (0.24 m)

Answer 1

Answer: The liquid having lowest freezing point is $FeI_3$

Explanation:

The expression for the depression in freezing point is given as:

$\Delta T_f=iK_f\times m$

Or,

$\text{Freezing point of pure solution}-\text{Freezing point of solution}=iK_fm$

where,

$\Delta T_f$ = depression in freezing point

i =  van't Hoff factor

$K_f$ = Cryoscopic constant

m = molality of the solution

For the given options:

Option A:  pure water

Pure water has a freezing point of 0°C

Option B:  aqueous KF (0.50 m)

Value of i = 2

So, molal concentration will be = $(0.50)\times 2=1m$

Option C:  aqueous sucrose (0.60 m)

Value of i = 1 (for non-electrolytes)

So, molal concentration will be = $(0.60)\times 1=0.6m$

Option D:  aqueous glucose (0.60 m)

Value of i = 1  (for non-electrolytes)

So, molal concentration will be = $(0.60)\times 1=0.6m$

Option E:  aqueous $FeI_3$ (0.24 m)

Value of i = 4

So, molal concentration will be = $(0.24)\times 4=0.96m$

As, the molal concentration of $FeI_3$ is the highest, so its freezing point will be the lowest.

Hence, the liquid having lowest freezing point is $FeI_3$