Final answer:
The thermometer in a distillation apparatus should be positioned at the level of the distillation head's sidearm to accurately measure the temperature of the vapor, allowing for effective separation of the components. A brief dip in temperature reading may occur due to the contraction of the thermometer fluid before it heats up. Correct thermometer placement is essential for the monitoring and success of the distillation process.
Step-by-step explanation:
The proper positioning of a thermometer in a distillation head during a distillation process is critical for accurately measuring the temperature of the vapors being produced. The thermometer should be positioned so its bulb is in line with or slightly below the sidearm of the distillation head to ensure it is in the path of the rising vapors but not in a direct contact with the liquid mixture. The significance of this placement is that it allows for the thermometer to record the temperature that represents the boiling point of the most volatile component, ensuring effective monitoring and control of the distillation process. This accurate temperature reading is essential for separating the components based on their boiling points.
It is important to note that an alcohol thermometer may show a temporary drop in the column of alcohol when placed in a hot liquid due to the contraction of the alcohol before it heats and expands. This phenomenon is temporary, and soon the temperature reading will stabilize and rise as the alcohol expands with heat. Following this, successful distillation can be achieved when the mixture is appropriately heated to vaporize the most volatile component (A), then condensing and collecting it separately from the less volatile component (B), as per Raoult's law.