Question

Assuming equal concentrations and complete dissociation, arrange these aqueous solutions by their freezing points. Highest to lowesta. CoBr3b. K2CO3c. LiNO3

Answer 1

Answer: LiNO3> K2CO3c > Co Br3

meaning that LiNO3 has the highest freezing point, and Co Br3 has the lowest freezing point

Explanation:

Freezing point depression is a colligative property and it depends on the number of solute particles dissolved.

According to the freezing point formula

ΔTf = i * Kf * m

Where kf is a constant, m is the molality and i is the van't Hoff factor.

Molality is defined as the number of moles per kg of solvent, which represents the number of moles dissolved and the van't Hoff factor (multiplling the number of molecules that dissociate)

The number of dissociating molecules is directly proportional to the van't Hoff value, the greater the freezing point depression lowering the freezing point.

The question assumes that equal concentrations (molality) and complete dissociation are the conditions.

Let's find out the number of ions generated by each solute:

LiNO3 → Li(+) + NO3(-) => 2 ions

Co Br3 → Co(+) + 3 Br(-) => 4 ions

K2CO3 → 2K(+) + CO3(2-) => 3 ions.

So, corresponding the highest generated particles with the lowest dressing point.

The freezing point from higher to lower in rank is LiNO3> K2CO3c > Co Br3 is the order.

Answer 2

The number of dissociating molecules is directly proportional to the Van't Hoff value.The freezing point of the given solvents in decreasing order is $\bold {LiNO_3> K_2CO_3 > Co Br_3}$.

Van't Hoff Equation for the depression in freezing point;

$\bold {\Delta T = i\ Kf\ m}$

Where,

Kf =      freezing point depression constant of the solvent .

i  =       Van't Hoff factor for the dissolved solute

m =      Molality

The number of dissociating molecules is directly proportional to the van't Hoff value. So, greater the freezing point depression means lower the freezing point.

At  equal concentrations (molality) and complete dissociation are the conditions.

The number of ions generated by each solute after ionization,

$\bold {LiNO_3 \rightarrow Li^+ + NO_3^- (2\ ions)}\\\\\bold {Co Br_3 \rightarrow Co^++ 3 Br^- ( 4\ ion)}\\\\\bold {K_2CO_3 \rightarrow 2K^+ + CO3^2^- (3\ ions)}}$

The highest generated particles cause the lowest depression point.

Therefore, the freezing point of the given solvents in decreasing order is $\bold {LiNO_3> K_2CO_3 > Co Br_3}$.

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