Assume, that a 25 lbs. bag of NaCl is applied to every 50kg ice on a road. As th

Question

Assume, that a 25 lbs. bag of NaCl is applied to every 50kg ice on a road. As the temperature dropped, the road surface froze at -12.0 0C. The density of the solution is d = 1.240 g/mL. Consider the solution before freezing for the concentration calculations.

Determine:

Concentration of the solution in M:

c = __________________

Concentration of the solution in w/w%:

c = __________________%

The mole fraction of NaClin the solution (xNaCl)

xNaCl =______________

The van’t Hoff coefficient (i)

i = ____________________

The degree of dissociation (a)

a = ___________________

Explanation / Answer

DTf = i*Kf*m

i = 2 as NaCl is having 2 particles

here water is the solvent so Kf = 1.86

[0-(-12)] = 2*1.86*m

m (molality) = 12 / 2*1.86

m = 3.23 moles /Kg

...................................................................................

Concentration of the solution in Molarity

1/m = (d/M) - (mA/1000)

where

m = molality

d = density of the solution

mA = molar mass of solute

(1/3.23) = (1.240/M) - (58.5/1000)

0.31 = (1.240/M) - 0.06

(1.240/M) = 0.37

M = 1.240/0.37

M = 3.35 moles/lt

..............................................................................................

(w/W)% = M*mol.wt/10*d

              = 3.35*58.5/10*1.240

              = 15.8 %

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