Why is thermometer placement important in distillation?
Also, why should the bulb of the thermometer be placed?
The bulb part of the thermometer is positioned near the side arm of the Y-adaptor so that it monitors the temperature of the vapors. If it is too low, it will be too close to the boiling liquid and will read higher than the true vapor temperature.
In this regard, why should the bulb of the thermometer be located just below the sidearm of the distilling flask?
The thermometer is positioned so the bulb is situated just below the sidearm of the 3-way. If the bulb is too the low, the heater would cause the temperature seen to be too high causing premature switching of the collecting flasks.
If the bulb of the thermometer or tip of the thermocouple is placed too high in the condenser, then the hot vapors are likely to condense before they reach the thermometer. This will result in the recorded temperature being lower than the actual boiling temperature of the vapor.