Concentration of solution problem please help?

The density of toluene (C7H8) is 0.867 g/mL, and the density of thiophene (C4H4S) is 1.065 g/mL. A solution is made by dissolving 8.10 g of thiophene in 250.0 mL of toluene.

a)Calculate the mole fraction of thiophene in the solution

b)Calculate the molality of thiophene in the solution

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

1 Answer

  • a)

    (8.10 g C4H4S) / (84.1396 g C4H4S/mol) = 0.096269 mol C4H4S

    (250.0 mL C7H8) x (0.867 g/mL) / (92.1384 g C7H8/mol) = 2.35244 mol C7H8

    (0.096269 mol C4H4S) / (0.096269 mol + 2.35244 mol) = 0.0393

    b)

    (0.096269 mol C4H4S) / ((250.0 mL C7H8) x (0.867 g/mL) / (1000 g/kg)) = 0.444 mol/kg = 0.444 m

    c)

    (0.096269 mol C4H4S) / (0.2500 L + (8.10 g / 1.065 g/mL / (1000 mL/L))) = 0.374 mol/L = 0.374 M

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