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. Stu- dents studied the dehydration of each of these 4 alcohols, which are all liquids at 25°C. Which of the following statements gives the most likely reason that the test tube was cooled in ice water, as shown in Figure 1? The test tube was most likely cooled in ice water to more readily:
Correct answer: A. Condense the vapour produced.
- A. Condense the vapour produced.
- B. Condense the liquid produced.
- C. Evaporate the liquid produced.
- D. Evaporate the vapour produced.
Explanation
Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporisation. A lower temperature is needed to reverse evaporation, this is the correct answer.
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About Scientific Reasoning
Scientific reasoning evaluates hypotheses through observations, variables, controls, measurements and experimental results. Questions involve identifying independent and dependent variables, recognising a fair test, interpreting tables or graphs, distinguishing evidence from opinion, and deciding whether data supports, rejects or leaves a hypothesis unresolved.
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