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Boiling point of water at 750 mm Hg is 99.63^@C . How much sucrose is to be added to 500 gof water such that it boils at 100^@C ? [Molal elevation constant of water is 0.52 K kg "mol"^(-1) ] |
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Answer» Solution : Elevation in BOILING point required `(Delta T_b) = 100 - 96.63^@ = 3.37^@ ` Mass of solvent (water), `w_1`= 500 g MOLAR mass of solvent, `M_1 = 18 g "mol"^(-1)` Molar mass of solute, `C_12H_22O_11 = 342 g "mol"^(-1)` APPLYING the formula, `M_2= (1000 K_b w_2)/(w_1 Delta T_b) " or " w_2 = (M_2 xx w_1 xx Delta T_b)/(1000 xx K_b)` Substituting the values, we get `w_2 = (342 g"mol"^(-1) xx 500 g xx 0.37 K)/(1000 g kg^(-1) xx 0.52 K kg "mol"^(-1)) = 121.67 g ` |
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