Question

Calculate the mole fraction of benzene in solution containing 30% by
mass in carbon tetrachloride.
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Answer 1

Solution :-

30 % m /m means 30 g of carbon tetrachloride (solute) in 100 g solution

• Mass of benzene(solvent ) = 100 - 30

• Mass of benzene(solvent) = 70 g

Step I : Moles of Benzene

• Mass of benzene(W) = 70 g

• Molar mass of benzene(M) = 6C + 6H = 72 +6 = 78 g

we know that ,

➺ n = W /M

➺ n = 70 / 78

➺ n = 0.89

Step 2 : Moles of carbon tetrachloride( CCl4)

• Mass of CCl4 (W') = 30 g

• Molar mass of CCl4 (M') = C + 4Cl  = 12 + 142 = 154 g

we know that ,

➺ n '= W '/M '

➺ n = 30 / 154

➺ n = 0.19

Step 3 : Mole fraction of benzene

As per the formula ,

➺ X = n / n + n'

➺ X = 0.89 / 0.89 + 0.19

➺ X = 0.89 / 4.68

➺ X = 0.2

Mole fraction of benzene is 0.2