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Benzene and toluene form iedal solution over the entire range of composition. The vapour pressure of pure benzene and naphthalene at 300 K are 50.71 mm Hg and 32.06 mm Hg respectively. Calculate the mole-fraction of benzene in vapour phase if 80 g of benzene is mixed with 100 g of toluene.

Solution

Given that

P^o_Benzene= 50.51 mm Hg

P^o_Naphthalene= 50.51 mm Hg

Mass of Benzene = 80 g

Mass of Toluene = 100 g

Molar mass of benzene(C₆H₆) = 6 × 12 + 6 × 1 = 78 g mol ^{- 1}

Molar mass of toluene(C₆H₅CH₃) = 6 × 12 + 5 × 1 + 12 + 3 × 1 = 92 g mol^{– 1}

Use the formula

Mole of benzene $(n_{A})$
$= \frac{Mass of bezene}{Molar mass of bezene (C_{6} H_{6})} = \frac{80}{78 g {mol}^{- 1}} = 1.025 mol .$

Mass of Toluene $(n_{B})$
$= \frac{Mass of toluene}{Molar mass of toulene (C_{7} H_{8})} = 1 = \frac{100}{92 g {mol}^{- 1}} = 1.087 m o l$

Mole fraction of benzene $(x_{A})$
$= \frac{1.025 mol}{(1.025 mol + 1.087 mol)} = \frac{1.025}{2.113} = 0.486$

Similarly

Mole fraction of toluene, X _Toluene =

1-X_Benzene= 1 - 0.486 = 0.514

Use the formula if Henry law

P_A = p^o_A × X_A

Partial vapour pressure of benzene, P_Benzene= p^o_Benzene × XB_enzene

P_Benzene=0.487 × 50.71 = 24.645 mm Hg

Similarly

Partial pressure of Toluene, P toluene = 0.514 × 32.06 = 16.48 mmHg

Use the formula of mole fraction using partial pressure

Mole fraction of benzene = \frac{P_{benzene}}{P_{benzene} + P_{Toluene}}

Plug the values we get

Mole fraction of benzene = 24.645 /(24.645 + 16.48 )

= 24.645/41.123 = 0.60

Some More Questions From Solutions Chapter

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Suppose a solid solution is formed between two substances, one whose particles are very large and the other whose particles are very small. What kind of solid solution is this likely to be?

Amongst the following compunds identify which are insoluble, partially soluble and highly soluble in water?
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Solutions

Benzene and toluene form iedal solution over the entire range of composition. The vapour pressure of pure benzene and naphthalene at 300 K are 50.71 mm Hg and 32.06 mm Hg respectively. Calculate the mole-fraction of benzene in vapour phase if 80 g of benzene is mixed with 100 g of toluene.

Some More Questions From Solutions Chapter

Calculate the osmotic pressure in pascals exerted by a solution prepared by dissolving 1.0 g of polymer of molar mass 185,000 in 450 mL at 37⁰C.

Suppose a solid solution is formed between two substances, one whose particles are very large and the other whose particles are very small. What kind of solid solution is this likely to be?

Amongst the following compunds identify which are insoluble, partially soluble and highly soluble in water?
(i) phenol (ii) toluene (iii) formic acid (iv) ethylene glycol (v) chloroform, (vi) pentanol.

Two liquids A and B boils at 145⁰C and 190⁰C respectively. Which of them has a higher vapour pressure at 80⁰C ?

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For Daily Free Study Material Join wiredfaculty

Solutions

Benzene and toluene form iedal solution over the entire range of composition. The vapour pressure of pure benzene and naphthalene at 300 K are 50.71 mm Hg and 32.06 mm Hg respectively. Calculate the mole-fraction of benzene in vapour phase if 80 g of benzene is mixed with 100 g of toluene.

Some More Questions From Solutions Chapter

Calculate the osmotic pressure in pascals exerted by a solution prepared by dissolving 1.0 g of polymer of molar mass 185,000 in 450 mL at 370C.

Suppose a solid solution is formed between two substances, one whose particles are very large and the other whose particles are very small. What kind of solid solution is this likely to be?

Amongst the following compunds identify which are insoluble, partially soluble and highly soluble in water?(i) phenol (ii) toluene (iii) formic acid (iv) ethylene glycol (v) chloroform, (vi) pentanol.

Two liquids A and B boils at 1450C and 1900C respectively. Which of them has a higher vapour pressure at 800C ?

Mock Test Series

NCERT Sample Papers

Entrance Exams Preparation

Calculate the osmotic pressure in pascals exerted by a solution prepared by dissolving 1.0 g of polymer of molar mass 185,000 in 450 mL at 37⁰C.

Amongst the following compunds identify which are insoluble, partially soluble and highly soluble in water?
(i) phenol (ii) toluene (iii) formic acid (iv) ethylene glycol (v) chloroform, (vi) pentanol.

Two liquids A and B boils at 145⁰C and 190⁰C respectively. Which of them has a higher vapour pressure at 80⁰C ?