Question

why should a special tube used for carrying out boiling point determination be thoroughly washed and dried before another determination is carried out before another determination

Answer 1

Answer:

There are a variety of methods by which a sample's boiling point can be determined, including distillation, reflux, and by using a Thiele tube. The most straightforward method uses a Thiele tube, and has the advantage of using less than 0.5mL of material.

Distillation Method

There are simpler methods than a distillation to measure a compound's boiling point, and it is recommended to explore other options (e.g. Thiele tube) if this is the only goal. However, if materials are limited, or if a purification is planned anyhow, a distillation can be used to determine a compound's boiling point. The distillation technique is discussed in great detail in Chapter 5.

A simple distillation should suffice for most situations (Figure 6.19), and at least 5mL of sample should be used in the distilling flask along with a few boiling stones or stir bar. As the bulk of the material distills, the highest temperature noted on the thermometer corresponds to the boiling point. A major source of error with this method is recording too low a temperature, before hot vapors fully immerse the thermometer bulb. 5 Be sure to monitor the thermometer periodically, especially when the distillation is active. Record the barometric pressure along with the boiling point.