1.

Calcualate the molarity and molality of 20% aqueous ehtanol `(C_(5) H_(5) OH)` solution by volume. (density of solution `= 0.96 g mL^(-1)`)

Answer» Correct Answer - C::D
`C_(2) H_(5) OH` is 20% by volume, i.e., `20 mL of C_(2) H_(5) OH` is dissolved in `100 mL` of solution
Volume of `H_(2) O = 100 - 20 = 80 mL`
Weight of `H_(2) O = 80 xx 1 = 80 g (d_(H_(2)O) = 1)`
Weight of solution `= 100 xx 0.96 = 96 g`
weight of `C_(2) H_(5) OH = 96 - 80 = 16 g`
`(Mw of C_(2) H_(5) OH = 12 xx 2 + 5 + 16 + 1 = 46)`
`:. M = (W_(2) xx 1000)/(Mw_(2) xx V_(sol)) = (16 xx 1000)/(46 xx 100) = 3.48`
`m = (W_(2) xx 1000)/(Mw_(2) xx W_(1)) = (16 xx 1000)/(46 xx 80) = 4.35`


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