Organic Chemistry Laboratory I - Chem 341

Quiz 5d

1. Why should you never heat a closed distillation system? (1 pt)

When molecules of a liquid are heated, they will enter the gas phase, resulting in a greater pressure on the walls of the vessel. This increased vapor pressure could lead to an explosion.

2. Does water have a higher or lower boiling point on the top of Mount Hood in Oregon, compared to Seattle Washington? (1 pt)

The boiling point of any liquid depends on the pressure of the system. The air pressure at high altitude is lower because there is less oxygen. Thus, water will boil at a slightly lower temperature on Mount Hood (elevation ~ 11,000 ft) compared to Seattle, which is at sea level.

3. Define the term reflux ratio as it pertains to a distillation. (1 pt)

Amount of condensate returning to still pot relative to the amount distilled.

Reflux ratio = Return/Distillate

Higher reflux ratio indicates a more efficient distillation.

4. Label the following reaction as an oxidation, reduction, or neither. (2 pts)

5. Consider the oxidation of cyclododecanol and answer the following questions:

(a) What is the oxidizing agent? (1 pt)

Bleach or sodium hypochlorite (NaOCl). However, the bleach needs to be protonated in order to react with cyclododecanol. So (HOCl) is the active agent. We will accept any of these answers.

(b) What qualitative test is performed to determine whether or not enough of the oxidizing agent has been added to the reaction? (2 pts)

Starch/Iodide test

A positive test turns the paper black and indicates excess bleach.

4. Consider the GC chromatogram below from a mixture of toluene and hexane and answer the following questions.

(a) Which peak is due to toluene? (1 pt)

Peak B which has retention time 0.557 is due to toluene. Toluene has a higher boiling point than hexane, which makes it elute more slowly.

(b) What is the percentage of hexane in this mixture? (1 pt)

Nearly 40%, the % hexane is proportional to the area of the peaks.