The vapour pressure of pure benzene at a certain temperature is 0.850 bar. A non-volatile, nonelectrolyte solid weighing 0.5 g is added to 39.0 g of benzene (molar mass 78 g / mol ). The vapour pressu

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The vapour pressure of pure benzene at a certain temperature is 0.850 bar. A non-volatile, nonelectrolyte solid weighing 0.5 g is added to 39.0 g of benzene (molar mass 78 g / mol ). The vapour pressure of the solution then is 0.845 bar. What is the molecular mass of the solid substance?

TestHub · Accepted Answer

P A ∘ ​ = 0.850 bar, P S ​ = 0.845 bar w = 0.5 g , m = ? weight of solvent (benzene) = 39.0 g and molecular weight of benzene = 78 g As we know, P A ∘ ​ P A ∘ ​ − P S ​ ​ = x B ​ = n A ​ n B ​ ​ 0.850 0.850 − 0.845 ​ = M A ​ w A ​ ​ M B ​ w B ​ ​ ​ = 78 39 ​ m 0.5 ​ ​ On solving, we get molecular mass of solid structure ( m ) = 170 g .

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