A solution is prepared by dissolving 12.5g of CH4N2O in 50.0mL of water. The res

Question

A solution is prepared by dissolving 12.5g of CH4N2O in 50.0mL of water. The resulting solution was found to have a density of 1.14g/mL. Assume the density of pure water is 1.00g/mL Use this to calculate:

a.) The mole fraction of CH4N2O in this solution

b.) The molality of CH4N2O in this solution

c.) The molarity of CH4N2O in this solution.

d.) The vapor pressure of this solution assuming it is ideas and that the vapor pressure of pure water is 26.3 torr.

e.) The freezing point of this solution.

f.) The Osmotic pressure of this solution at 25 degrees Celsius.

Explanation / Answer

a)

mass = 12.5 g

MW = 60.06

mol = mass/MW = 12.5/60.06 = 0.208

mol of water = mass/MW = 50/18 = 2.777

then

mol frac of CH4N2O = 0.208/(0.208+2.777) = 0.0696

b)

molality = mol solute / kg solvent

molality = 0.208/(50/1000) = 4.16

c)

molarity = mol/L

M = 0.208/(50/1000) = 4.16 M

d)

Pºurea = 71.9 torr

Pºwater = 26.3 torr then

Pº = xa*Pºa + xa*Pºb = 0.208*71.9 + (1-0.208)*26.3 = 35.7 torr

e)

Kf for water = -1.86

dT = -K*m = -1.86*4.16 = -7.73

T = 0 - 7.73 = -7.73 ºC

f)

PI = M*RT = 4.16*0.082*298 = 101.65 atm

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