Passage IV

Alcohols are carbon compounds containing a hydroxyl (OH) group. Alkenes are carbon compounds containing at least 1 carbon-carbon double bond (C=C).

Dehydration (removal of H₂O) of Alcohol W in the presence of phosphoric acid (H₃PO₄) produces H₂O and a mixture of 4 alkenes (Alkenes 1-4) that each contain only 1 C=C bond:

Dehydration of each of 3 other alcohols (Alcohols X, Y, and Z) produces H₂O and 2 or more of Alkenes 1—4. Stu­dents studied the dehydration of each of these 4 alcohols, which are all liquids at 25°C.

Experiment

In each of 4 trials, the students performed Steps 1-5:

1. A 2.30 g sample of Alcohol W, X, Y, or Z was placed in a flask.

2. A 0.5 mL portion of (H₃PO₄) was added to the flask, and an apparatus for distillation (evaporation of one or more components of a liquid mixture in one vessel and con­densation of the vapors in another vessel) was assem­bled (see Figure 1).

3. The contents of the flask were boiled at 1 atmosphere (atm) of pressure in a heated sand bath. All the compo­nents of the product mixture that distilled before the vapor temperature reached 115 ° C were collected in a test tube that was cooled in ice water.

4. Two mL of saturated salt solution was added to the test tube. The test tube was covered and shaken, and its con­tents were allowed to settle into 2 layers.

5. The percent composition of the top layer (the mixture of alkene products only) was determined (see Table 1).