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Nikitich [7]
3 years ago
11

What is the molality of a solution of water and KCl if the freezing point of the solution is –3°C? (Kf = 1.86°C/m; molar mass of

water = 18
g.
Chemistry
2 answers:
Elina [12.6K]3 years ago
4 0
Some of the solutions exhibit colligative properties. These properties depend on the amount of solute dissolved in a solvent. These properties include freezing point depression, boiling point elevation, osmotic pressure and vapor pressure lowering. Calculations are as follows:

<span> ΔT(freezing point)  = (Kf)mi
3  = 1.86 °C kg / mol (m)(2)
3 =3.72m
m = 0.81 mol/kg</span>

a_sh-v [17]3 years ago
3 0

Answer : The molality of a solution is, 0.806 mole/Kg

Explanation :

First we have to calculate the Van't Hoff factor (i) for KCl.

The dissociation of KCl will be,

KCl\rightarrow K^++Cl^-

So, Van't Hoff factor = Number of solute particles = K^++Cl^- = 1 + 1 = 2

Now we have to calculate the molality of solution.

Formula used for lowering in freezing point :

\Delta T_f=i\times k_f\times m

or,

T_f^o-T_f=i\times k_f\times m

where,

\Delta T_f = change in freezing point

T_f = temperature of solution = -3^oC

T^o_f = temperature of pure water = 0^oC

k_f = freezing point constant  = 1.86^oC/m

m = molality  = ?

i = Van't Hoff factor = 2

Now put all the given values in this formula, we get the molality of the solution.

0^oC-(-3^oC)=2\times (1.86^oC/m)\times m

m=0.806mole/Kg

Therefore, the molality of a solution is, 0.806 mole/Kg

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