Answer :
Final answer:
The capillary tube is positioned next to the thermometer bulb to ensure accurate temperature measurements, as it allows the substance within to be subjected to the same temperature as the thermometer and facilitates direct observation of phase changes in conjunction with the temperature scale.
Explanation:
Positioning the capillary tube next to the thermometer bulb in experiments like the determination of melting points in a Thiele tube is crucial for accurate temperature measurements. When the capillary tube containing the sample is secured to the thermometer with a tiny rubber band and positioned flush with the bottom of the thermometer, it ensures that the substance in the capillary tube is subjected to the same temperature as the thermometer bulb. During the heating process, the substance in the capillary and the liquid inside the thermometer expand with increasing temperature. Hence, their temperatures should be equal for correct readings.
Not only does this guarantee precise temperature monitoring, but it also allows the observation of phase changes, such as when the sample transitions from solid to liquid, directly against the temperature scale. This direct correlation simplifies determining the exact melting point temperature of the substance in the capillary tube.
