Suppose you have been given the task of distilling a mixture of hexane + toluene. Pure hexane has a refractive index of 1.375 an
d pure toluene has a refractive index of 1.497. You collect a distillate sample which has a refractive index of 1.441. Assuming that the refractive index of the hexane + toluene mixture varies linearly with mole fraction, what is the mole fraction of hexane in your sample?
How the refractive index of the hexane + toluene mixture varies linearly with mole fraction, it means that the mole fraction is the fraction that each pure index contribute for the mixture index, so, calling <em>xh</em> the mole fraction of hexane and <em>xt</em> the mole fraction of toluene:
1.375xh + 1.497xt = 1.441
And, xh + xt = 1 (because there are only hexane and toluene in the mixture), so xt = 1- xh
