Question

Calculate the mass of ascorbic acid (Vitamin C, `C_(6)H_(8)O_(6)`) to be dissolved in 75g of acetic acid to lower its melting point by `1.5^(@)C. K_("f")=3.9" K kg mol"^(-1)`.
Since, lowering of melting point is given apply the formula for lowering of melting point, i.e.,
`DeltaT_("f")=K_("f").m`
`DeltaT_("f")=(K_("f").W_(B))/(M_(B)xxW_(A))" or "W_(B)=(DeltaT_("f").M_(B).W_(A))/(K_("f"))`

Answer 1

Mass of ascorbic acid `(W_(A))=75" g"=0.075" kg"`
Depression in melting point `(DeltaT_("f"))=1.5^(@)C=1.5" K"`
Molar mass of ascorbic acid `(M_(B))=(12xx6)+(8xx1)+(16xx6)=176" g mol"^(-1)`
Molal depression constant `(K_("f"))=3.9" K kg mol"^(-1)`
`W_(B)=((176" g mol"^(-1))xx(1.5" K")xx(0.075" kg"))/((3.9" K kg mol"^(-1)))=5.08" g"`