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The density of toluene (C7H8) is 0.867 g/ml, and the density of thiopene (C7H4S) is...

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spock6 | Student, Undergraduate | (Level 1) Honors

Posted May 16, 2013 at 11:05 AM via web

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The density of toluene (C7H8) is 0.867 g/ml, and the density of thiopene (C7H4S) is 1.065 g/mL. A solution is made by dissolving 15.0 g thiopene in 250.0 mL of toluene.

a) calculate the mole fraction of thiopene in the solution

b) calculate the molality of thiopene in the solution

c) assuming that the volumes of the solute and solvent are additive, what is the molarity of thiopene in the solution?

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llltkl | College Teacher | (Level 3) Valedictorian

Posted May 16, 2013 at 2:44 PM (Answer #1)

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The solution is made up by dissolving 15.0 g thiopene in 250.0 mL of toluene.

Density of toluene (C7H8) is 0.867 g/ml, and the density of thiopene (C7H4S) is 1.065 g/mL.

So, 250.0 mL toluene = 250*0.867 g toluene = 216.75 g toluene.

Molar mass of toluene is (7*12+8*1) = 92

Molar mass of thiophene is (7*12+4*1+32) = 120

Therefore,

a) mole fraction of thiopene in the solution = `(15/120)/(15/120+216.75/92)`

= `0.125/(0.125+2.356)`

= 0.05

b) To calculate the molality of thiophene in solution,

216.75 g solvent is associated with 15/120 = 0.125 mole of the solute (thiophene).

So, 1000 g solvent should be associated with 0.125*1000/216.75 = 0.5767 moles of the solute.

Hence, the molality of thiophene is 0.5767 m.

c) The volumes of the solute and solvent are additive. So, total volume of the solution is (15/1.065 + 250) = 264.0845 mL.

264.0845 mL solution contains 0.125 mole solute (thiophene).

So, 1000 mL solution should contain 0.125*1000/264.0845 = 0.473 moles.

thus, the molarity of thiophene is 0.4733 m.

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