In a simple distillation setup, how far should the thermometer be inserted into the distillation apparatus for accurate measurement of the boiling point?

• A. The bulb of the thermometer should be positioned just below the side arm of the distillation flask, at the level where vapor exits.
• B. The thermometer should be placed at the very top of the distillation column, far above the side arm.
• C. The thermometer should be inserted only halfway into the neck of the distillation flask, not reaching the side arm.
• D. The thermometer should be fully immersed in the liquid being distilled.

Answer: (A)

Verified step by step guidance

1. Understand the purpose of the thermometer in a simple distillation setup: it is used to measure the temperature of the vapor, which corresponds to the boiling point of the liquid being distilled.
2. Recognize that the thermometer bulb must be placed where it can accurately sense the temperature of the vapor, not the liquid or the air above it.
3. Identify the location where vapor exits the distillation flask, which is typically at the side arm connecting the flask to the condenser.
4. Position the bulb of the thermometer just below the side arm, so it is in the path of the vapor leaving the flask, ensuring an accurate reading of the boiling point.
5. Avoid placing the thermometer too high (above the side arm) or fully immersed in the liquid, as these positions will not give an accurate vapor temperature measurement.