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What mass of NaCl (molar mass "58.5 g mol"^(-1)) must be dissolved in 65 g of water to lower the freezing point by 7.5^(@)C ? The freezing point depression constant, K_(f) for water is "1.86 K kg mol"^(-1). Assume that van't Hoff factor for NaCl is 1.87.

Answer»


Solution :`DeltaT_(F)=iK_(f)m=iK_(f)(w_(2))/(M_(2))xx(1)/(w_(1))xx1000,""7.5=1.87xx1.86xx(w_(2))/(58.5)xx(1)/(65)xx1000 or w_(2)=8.199g.`


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