1.

15 g of an unknown molecular substance was dissolved in 450 g of water. The resulting solution freezes at - 0.34^(@)C. what is molar mass of the substance ? (K_(f)" for water" = 1.86k kg " mol"^(-1))

Answer»

SOLUTION :`W_(B) = 15 g, W_(A) = 450` g
`Delta T_(F) = 0.34^(@) C , K_(f) = 1.86 , M_(B)` = ?
`Delta T_(f) = K_(f) xx (W_(B) xx 1000)/(M_(B) xx W_(A))`
`0.34 = 1.86(15 xx 1000)/(M_(B) xx 450)`
0.34 = `(61.99)/(M_(B))`
`M_(B) = (61.99)/(0.34)`
` = 182.35 g MOL^(-1)`


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