calculate the mole fracton of benzene ina solution containing 30% by mass of it in carbon tetrachloride

Let the total mass of the solution be 100 g and the mass of benzene be 30 g.
∴ Mass of carbon tetrachloride = (100 - 30)g = 70 g
Molar mass of benzene (C6H6) = (6 × 12 + 6 × 1) g mol - 1
= 78 g mol - 1
∴ Number of moles of C6H6 =30/78 mol
= 0.3846 mol
Molar mass of carbon tetrachloride (CCl4) = 1 × 12 + 4 × 355
= 154 g mol - 1
∴ Number of moles of CCl4 = 70/154 mol
= 0.4545 mol
Thus, the mole fraction of C6H6 is given as:
= 0.3846 / (0.3846 +0.4545)
= 0.458