How to Calculate Distillation Range

Many chemists use distillation to identify unknown organic compounds by determining their boiling point and then comparing it to published data. Distillation is also commonly used in the purification of organic compounds. For example, you might use distillation to separate your product from unwanted side products. During distillation, an unknown or impure compound is heated until it boils. Then the vapors are collected and condensed. Distillation is usually much faster and easier to perform -- especially for compounds with very high boiling points -- under reduced pressure or vacuum. However, you must then calculate the distillation range at atmospheric pressure from the value under vacuum with a nomograph.

Things You'll Need

• Vacuum distillation apparatus
• Pressure gauge
• Nomograph or printer
• Pen or pencil
• Ruler

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Instructions

1. • 1

     Distill your compound under reduced pressure.

   • 2

     Carefully record the boiling point and the pressure inside the distillation apparatus with a pressure gauge.

   • 3

     Print a nomograph, if you do not have one already.

   • 4

     Mark the pressure you recorded on the far right line of the nomograph, usually labeled "pressure," with a pen or pencil.

   • 5

     Mark the boiling point you recorded during the distillation on the far left line of the nomograph, usually labeled "observed," with a pen or pencil.

   • 6

     Draw a line between the two points with a ruler.

   • 7

     Read off the point where the straight line intersects the middle line of nomograph, usually labelled "atmospheric." This is the boiling point of your compound at atmospheric pressure.