How many moles of sucrose should be dissolved in 500 g of water so as to get a solution which has a difference of 104∘C between boiling point and freezing point. (Kf=1.86Kkgmol−1,Kb=0.52Kkgmol−1).
0.840
Tb−Tf=104∘C
ΔTb=Tb−T∘b
ΔTf=T∘f−Tf
(ΔTb+T∘b)−(Tf−ΔTf)=104∘C\
ΔTb+100−0+ΔTf=104
ΔTb+ΔTf=4
Kbm+Kfm=4
(0.52+1.86)m=4
2.38×m=4
m=1.68
moles500×1000=1.68
moles =1.682=0.84 moles