Question

My question is why when I am distillating a mixture to obtain pure liquids, the boiling point ranges are lower than literature values for the boiling point of each of them. For example, I am distillating a mixture of diethyl ether isopentanol and isopentyl propionate. My distillates were separated at 32-33, 125-127 and 145-146. All these numbers are lower for each of them than their literature values that are 34.4 for diethyl ether, 130.8 for isopentanol and 173 for isopentyl propionate.

Why are the distillation ranges lower than the literature values?

Answer 1

Distallation mixture may contain some impurities then their boiling point ranges are lower than literature values for the boiling point of each of the them. Becaue impurity can increase the vapor pressure of the liquid as the impurity is volatile, then its vapor pressure reach the atmospheric pressure before its boiling point temperature.

Some times molecular atrraction forces between two liquids may be weaker then the attraction forces between same molecules of one liquid. Then also vapor pressure of mixture is greater than the summation of vapor pressures of pure liquids, this also lower the boiling point of liquids during distillation. But for last liquid boiling point range lowered by almost 30 degrees C, this indicates mixture may contain highly volatile impurity.