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The vapour as solution of a 5% non vola...

The vapour as solution of a 5% non volatile organic substance at 373 Ks745 mm. Calculate the molar mass of the solute ?

Text Solution

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Mass of the solute `(w_2)`=5g
Mass of the solution =100 g
Mass of the solvent `(w_1)` = `100 - 5`=95 g
Vapour pressure ofpure water at 373K `(p^@)`} = 760 mm
Vapour pressure of the solution at 373K `(p)`} = 745 mm(given)
Molar mass of solvent `(M_1)` =18 g `"mol"^(-1)`
Molar mass of solute = ?
`(p^o-p)/p^0`= `(w_2/M_2) xx(M_1/w_2)`
Substituting the values given
`(760 - 745)/760`= `(5g xx18g "mol"^-1)/(95g xxM_2) `
`M_2`=`(5xx18xx 760)/(15x95)` g `mol^(-1)`
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