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1.00g of a non-electrolyte solute dissol...

1.00g of a non-electrolyte solute dissolved in 50g of benzene lowered the freezing point of benzene by 0.40K. The freezing point depression constant of benzene is 5.12K `mol^-1` . Find the molar mass of the solute.

Text Solution

Verified by Experts

The correct Answer is:
`256 g mol^(-1)`
`W_(B) = 1.0g , W_(A) = 50.0g = 0.05 kg`
`K_(f) = 5.12 K kg mol^(-1)`
`Delta T_(f) = 0.40 K`
`M_(B) = ?`
`Delta T_(f) = K_(f) xx (W_(B))/(M_(B)) xx (1)/(W_() (kg))`
`M_(B) (K_(f) xx W_(B))/(Delta T_(f) xx W_(A) (kg))`
`= (6.12 K kg mol^(-1) xx (1.0 g))/((0.40 K) xx (0.05 kg))`
`= (5120)/(4 xx 5) g mol^(-1) = 256 g mol^(-1)`
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