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Standard XII

Chemistry

Relative Lowering of Vapour Pressure

The vapour pr...

Question

The vapour pressure of benzene at a certain temperature is 640 mm. of Hg. A non-volatile and non-electrolyte solid, weighing 2.175 g is added to 39.08 g of benzene. If the vapour pressure of the solution is 600 mm of Hg. What is the molecular weight of solid substance?

49.50

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59.60

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69.40

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79.82

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Solution

The correct option is C 69.40
According to Raoults law:
$\Rightarrow \frac{n_{s o l u t e}}{n_{s o l v e n t}} = \frac{P_{s o l v e n t}^{\circ} - P_{s o l u t i o n}}{P_{s o l u t i o n}}$
$\frac{P_{0} - P_{s}}{P_{0}} = \frac{w \times M}{m \times W}$
w=mass of solute
W=mass of solvent
m= molar mass of solute
M= molar mass of solvent

$\frac{640 - 600}{640} = \frac{2.175 \times 78}{m \times 39.08}$

(M for $C_{6} H_{6} = 78)$

$m = \frac{2.175 \times 78 \times 640}{40 \times 39.08}$
$= 69.45 \approx = 69.4$

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Similar questions

Q. The vapour pressure of pure benzene at a certain temperature is 640 mm Hg. A non-volatile non-electrolyte solid weighing 2.175 g is added to 39 g of benzene. The vapour pressure of the solution is 600 mm Hg. What is the molecular weight of the solid substance?

Q. The vapour pressure of benzene at a certain temperature is

640

mm of Hg. A non-volatile and non-electrolytic solid, weighing

2.175

g, is added to

39.08

g of benzene. The vapour pressure of the solution is

600

mm of Hg. What is the molecular mass (in AMU) of the solid substance?

Q. The vapour pressure of pure benzene and at a certain temperature is

640 m m

H g

. A non-volatile, non-electrolyte solid weighing

2.175 g

is added to

39.0 g

of benzene. The vapour pressure of the solution is

600 m m

H g

What is the molecular weight of the solid substance?

The vapour pressure of benzene at a certain temperature is 640mm of Hg. A non volatile and non electrolyte solid weighing 2.175 g is added to 39.08 g of benzene. The vapour pressure of the solution is 600mm of Hg. What is the molecular mass of the solid substance?

Q. The vapour pressure of pure benzene at certain temperature is

640 m m

H g

. A non-volatile non-electrolyte solid weighing

2.175 g

is added to

39.0 g

of benzene. The vapour pressure of the solution is

600 m m

H g

. What is the molar mass of the solid substance?

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The vapour pressure of benzene at a certain temperature is 640 mm. of Hg. A non-volatile and non-electrolyte solid, weighing 2.175 g is added to 39.08 g of benzene. If the vapour pressure of the solution is 600 mm of Hg. What is the molecular weight of solid substance?

The correct option is C 69.40According to Raoults law: ⇒nsolutensolvent=P∘solvent−PsolutionPsolution P0−PsP0=w×Mm×W w=mass of solute W=mass of solvent m= molar mass of solute M= molar mass of solvent 640−600640=2.175×78m×39.08 (M for C6H6=78) m=2.175×78×64040×39.08 =69.45≈=69.4