Illustrated Guide to Home Chemistry Experiments

Chapter 6 Laboratory: Separating Mixtures 99

oALIpToN ACTIvITIES

If you have enough time and the required materials,

consider performing these optional activities:

• Repeat the distillation, transferring the original
  distillate to the distillation vessel for redistillation. The
  volume of the second distillate will be smaller than
  the volume produced during the first distillation, so
  you’ll either need to distill considerably more than
  100 mL originally or else use a smaller volumetric
  flask to determine the density of the second distillate.
  Alternatively, you can use a graduated cylinder to
  determine the density of the second distillate, with
  some loss of accuracy.


• Run the distillation a third time, and determine the
  density (and ethanol concentration) of the third
  distillate.

Item Data

A. Volumetric flask _________.___ g

B. Volumetric flask with 100 mL 70% ethanol _________.___ g

C. Mass of 100 mL 70% ethanol (B – A) _________.___ g

D. Density of 70% ethanol (C/100) _________.___ g/mL

E. Volumetric flask with 100 mL distilled ethanol _________.___ g

F. Mass of 100 mL distilled ethanol (E – A) _________.___ g

G. Density of distilled ethanol (F/100) _________.___ g/mL

TABLE 6-2: Distillation of ethanol—observed and calculated data

LINGHBoGHI I poINT AzEoTRopES

Hydrochloric acid is one familiar example of a negative

(high-boiling) azeotrope. Pure hydrogen chloride has

a boiling point of -84°C and pure water a boiling point

of 100°C. A solution of 20.2% hydrogen chloride (by

weight) in water has a boiling point of 110°C, higher than

the boiling point of either component. This means that

boiling a solution of hydrochloric acid of any concentration

eventually produces a solution of exactly 20.2%

hydrogen chloride by weight. If the starting solution is

more dilute, water is driven off until the solution reaches

20.2% concentration. If the starting solution is more

concentrated, hydrogen chloride gas is driven off until the

solution reaches 20.2% concentration.