Question

calculate the mole fraction if benzene in solution containing 30% by mass in tetrachloride ?

Answer 1

Mass % is given so take total mass of the solution = 100 g
Then the mass of benzene = 30 % of 100 = 30 g.
Mass of carbon tetrachloride = total mass - mass of benzene
=(100 − 30)g
= 70 g
Molar mass of benzene (C6H6) = 6 × 12 + 6 × 1 = 78 g mol−1
Use the formula

Number of moles of C6H6 = 30 /78 = 0.3846 mol
Molar mass of carbon tetrachloride (CCl4) = 1 × 12 + 4 × 355 = 154 g mol−1

Use same formula again we get

Number of moles of CCl4 = 70/154 = 0.4545 mol
Use the formula of mole fraction

Mole fraction of benzene =0.3846 /(0.3846+ 0.4545) = 0.458

Answer 2

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 × 35.5
= 154 g mol - 1
∴ Number of moles of CCl4 = 70/154 mol
= 0.4545 mol
Thus, the mole fraction of C6H6 is given as:

number of moles of C6H6 / number of moles of C6H6 + number of moles of CCL4

= 0.3846 / (0.3846 +0.4545)
= 0.458

this is your answer.....