Question

The vapour pressure of pure benzene at a certain temperature is 262 bar .At the same temperature the vapour pressure of a solution containing 2g of non-volatile ,nin-electrolytic solid is 100 g of benzene is 256 bar .What us the molar mass of solid?​

Answer 1

Answer:

the answer is 68.12g

Explanation:

• see the picture below for explanation

Answer 2

Answer:

$\bigstar{\bold{Molar\:mass=68.12\:g/mol}}$

Explanation:

$\Large{\underline{\underline{\bf{Given:}}}}$

• Vapour pressure of pure benzene (p₁)⁰ = 262 bar
• Vapour pressure of solution (p) = 256 bar
• Molar mass of benzene (M₁)= 72 + 6 = 78 g/mol
• Weight of benzene (w₁) = 100 g
• Weight of solid (w₂) = 2 g

$\Large{\underline{\underline{\bf{To\:Find:}}}}$

• Molar mass of the solid (M₂)

$\Large{\underline{\underline{\bf{Solution:}}}}$

→ We have to find the molar mass of the solid.

→ By the relation between relative lowering of vapour pressure and mole fraction of the solvent we know that,

 $\dfrac{(p_1)^{o}-p_1 }{(p_1)^{o} } =\dfrac{w_2\times M_1}{w_1\times M_2}$

→ Substituting the given datas we get,

  $\dfrac{262\:bar-256\:bar}{262\:bar} =\dfrac{2\:g\times 78\:g\:mol^{-1} }{100\:g\times M_2 }$

→ Solving it we get,

  $\dfrac{6\:bar}{262\:bar} =\dfrac{156\:g\:mol^{-1} }{100\times M_2}$

→ Cancelling 6 and 156 on both sides

  $\dfrac{1}{262}=\dfrac{26\:g\:mol^{-1} }{100\times M_2}$

→ Cross multiplying,

  100 × M₂ = 262 × 26 g/mol

            M₂ = 6812/100 g/mol

            M₂ = 68.12 g/mol

→ Hence the molar mass of the solid is 68.12 g/mol

  $\boxed{\bold{Molar\:mass=68.12\:g/mol}}$

$\Large{\underline{\underline{\bf{Notes:}}}}$

→ Raoult's law state that for a solution of volatile liquids, the partial pressure of each component of the solution is directly proportional to mole fraction present in solution.

p₁ $\propto$ x₁