Can someone help me with mole fraction, molality and molarity?

Question

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 17.0 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?

Answer 1

a) moles C4H4S = 17.0 / 84.14 = 0.202
Mass toluene = 250 x 0.867 = 216.8 g
moles toluene = 216.8 / 92.14 = 23.5
Total moles = 0.202 + 23.5 =25.5
mole fraction = 0.202 / 25.5 = 0.0791
b) m = 0.202 / 0.2168 Kg = 0.932
c) volume thiophene = 17 / 1.065 = 16.0 mL = 0.016 L
total volume = 0.016 + 0.250 = 0.266 L
M = 0.202 / 0.266 = 0.759

Answer 2

Toluene Density

Answer 3

C4H4S ==> 4*12.011 + 4*1.00794 + 32.066 = 84.14176 g/mol
17/84.14176 ≈ 0.2020400 mol.
C7H8 ==> 7*12.011 + 8*1.00794 = 92.14052 g/mol
(250.0)(1.065) / 92.14052 ≈ 2.889608 mol

(a) 0.2020400 / (0.2020400 + 2.889608) ≈ 0.06535025 ≈ 6.535%

(b) 0.2020400 mol. / 0.2500 L ≈ 0.80816 ≈ 0.8082 mol/L molality

(c) (0.2020400 mol.) / (0.2500 + 17/867) ≈ 0.7493847 ≈ 0.7494 mol./L molarity