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Question
A solution containing 8.44 g of sucrose in 100 g of water has a vapour pressure 4.56 mm of Hg at 273 K. If the vapour pressure of pure water is 4.58 mm of Hg at the same temperature, calculate the molecular weight of sucrose.
Solution
`"P"_"A"^° = 4.56 "mm of Hg"`
`"P"_"A" = 4.56` mm of Hg
`("P"_"A"^° - "P"_"A")/"P"_"A"^° = X_"B" = ("n"_"B")/("n"_"B" +"n"_"A")`
`(4.58 - 4.56)/4.58 = (8.44/"M"_"B")/(100/18 + 8.44/"M"_"B")`
`0.02/4.58 = 8.44/"M"_"B" xx (18"M"_"B")/((100 "M"_"B" + 151.92))`
`0.02/4.58 =(8.44 xx 18)/(100 "M"_"B" + 151.92)`
`100 "M"_"B" + 151.92 = (8.44 xx 18 xx 4.58)/0.02`
MB = 346.38 amu
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