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).
23. What was the most likely purpose of the sand bath shown in Figure 1?
Your Answer is
Correct Answer is B
Explanation
General knowledge questions.
Sand bath is generally used for high-temperature heating. The purpose of use is to heat the sand first, and then indirectly heat the flask. The effect is to make the heating more uniform (this is also the principle of frying chestnuts with small stones)