Question

You are performing a simple distillation of roughly 50:50 liquid solution containing two components, hexane and nonane You place 15 ml of the mixture in a round bottom flask, and then collect the distillate sequentially as four three ml samples labeled S1, S2, S3, and S4. Pure hexane has a refractive index of 1.375 and pure nonane has a refractive index of 1.407. You measure a refractive index of 1.3948 for one of the four samples. Assuming the refractive index varies linearly with mole fraction, estimate the mole fraction of hexane in this sample.

Answer 1

Answer:

0.38  

Explanation:

As you go from 0 % hexane (χ = 0) to 100 % hexane (χ = 1), the refractive index decreases from 1.407 to 1.375, a decrease of 0.032.

From 1.407 to 1.3948, the decrease is 0.0122 .

That is 0.0122/0.032 = 0.38 of the distance from χ = 0 to χ = 1.

The mole fraction of hexane is 0.38.

The diagram below is a plot of refractive index vs. the mole fraction of hexane. It shows that the refractive index drops to 1.3948 when χ = 0.38.