Question

What is the percent by mass of iodine needed to reduce the freezing point of benzene to `3.5^(@)"C"`? The freezing point and cryoscopic constant of pure benzene are `5.5^(@)"C"` and `5.12K/m` respectively.

Answer 1

`Delta"T"_(f)="T"_(f)^(0)-"T"_(f)="K"_(f)."m"`
`5.5^(@)"C"-3.5^(@)"C"=5012xxm`
`m=2/5012=0.39" molal"`
`therefore ` Mass of iodine needed for 1000g of benze`=mxx"molecular mass of iodine "I^(2)`
`=0.39"mol//kgxx254g//mol=99.06g//kg`
`therefore` 1000g+99.06g solution contain `99.06g "I"^(2)`
100g solution contains `99.06gxx100/1099.06g=9.01%`