1) Ethanol has a Kb of 1.22 Degrees C/m and usually boils at 78.4 Degrees Celciu

Question

1) Ethanol has a Kb of 1.22 Degrees C/m and usually boils at 78.4 Degrees Celcius. How many mol of an nonionizing solute would need to be added to 47.84 g ethanol in order to raise the boiling point to 86.30?

2) You dissolve 9.870 grams of substance Y (whose molar mass is 122.560 g/mol) in .650 L of water (whose molar mass is 18.02 g/mol). The density of water at this temperature is .9750 g/mL. Calculate the mole fraction of substance Y.

3) Calculate the osmotic pressure of a solution containing 1.502 g of (Nh4)2SO4 in 1 L at 36.54 Degrees Celcius. (The gas constant is .08206 Latm/molK. The molar mass of (Nh4)2SO4 is 132.16)

Explanation / Answer

Ans 1 :

Boiling point elevation = kb . m

elevation = 86.30 - 78.4 = 7.9oC

putting values :

7.9 = 1.22 x m

m = 6.475 m

Molality = no. of moles of solute / mass of solution in kg

6.475 = n / 0.04784

n = 0.31 moles

So number of moles to be added = 0.31 mol

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