Answer :
In melting point analysis, it's crucial to pack a capillary tube carefully by tapping it on a bench or using a longer tube, ensuring the sample is no higher than 3 mm to maintain accuracy. It is important to avoid packing the tube too loosely, which can be a common mistake when preparing the sample. So, the correct option is a. tap it on the bench.
When packing a capillary tube for melting point analysis, it is important to take care not to pack the tube too loosely. A common error to avoid is failing to tap the tube sufficiently on the bench to pack the solid at the bottom (option a).
The correct process involves jabbing the open end of a capillary tube into the solid compound to fill it, then inverting the tube and gently tapping it on the benchtop to settle the compound. Alternatively, dropping the tube through a longer narrow tube can also help in packing the sample tightly.
The compound must be dry for accurate results, as moisture can introduce impurities that alter the melting range. The sample packed in the capillary tube should be no higher than 3 mm to avoid broadening the melting range.
Moreover, inserting the capillary tube in a melting point apparatus requires careful handling to ensure that samples do not come loose and to obtain a precise melting point. Intense care is needed during this process to prevent breaking the capillary tube (option b) or any other mishandling that might affect the experiment's results. So, the correct option is a. tap it on the bench.
