1.

Thevapourpressureof 2.1% solutionof a non- electrolyte in waterat 100^(@) C is755mm Hg. Calculatethe molarmass of thesolute .

Answer»

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Solution :At `100^(@)C`vapourpressure of WATER`=P_(o)`= 760mm Hg
VAPOURPRESSUREOF the solutions= P= 755 mm Hg
Sincethe solutionis 2.1by mass
Mass of solute (non- electrolyte) =`W_(2) =2.1 g`
Mass ofwater`=W_(1) =100 -2.1 =97.9 g`
Molarmass ofwater= `M_(1) =18 g mol^(-1)`
Molarmass ofnon- electrolyte `=M_(2)= ?`
`(P_(o) -P)/(P_(o)) = (W_(2) xx M_(1))/(W_(1) xx M_(2))`
`:.M_(2)= ((P_(o))/(P_(o) - P)) xx (W_(2) xx M_(1))/(W_(1)) = (700xx 2.1 xx 18)/((760 -755) xx 97.9) = 58.69 g mol^(-1)`


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