In melting point determination, why shouldn't a substance be re-melted? (i.e. why should we not re-melt a substance that has previously been melted in a melting point tube?)
Dat is bcos ur thermometer has cooled nd so has ur parafin oil(if it was used)so remeltin wud only give u wrong values...its advisable 2 go ova d process again n wit a diff capilary tube
In melting point determination, it is generally recommended not to re-melt a substance that has already been melted in a melting point tube. Here are a few reasons for this:
1. Degradation of the substance: Each time a substance is melted, there is a potential risk of chemical decomposition or degradation. The repeated exposure to heat during successive melting can lead to undesirable changes in the chemical structure of the substance, affecting its purity and ultimately the accuracy of the melting point determination.
2. Contamination: Re-melting a substance can introduce impurities or contaminants into the sample. Any impurities present in the melting point tube or the surrounding environment may contaminate the sample during subsequent melting. This can result in inaccurate melting point measurements.
3. Glass memory effect: Melting point tubes used in melting point determination are typically made of glass. Glass has a property known as the "glass memory effect," which means that it retains the shape or characteristics of substances heated in it. If you re-melt a previously melted substance in the same melting point tube, there is a possibility that residual material from the previous determination could remain in the tube and influence the current measurement.
To obtain accurate and reliable results in melting point determination, it is generally recommended to use a fresh portion of the sample and a clean melting point tube for each measurement. This ensures that only the pure sample is being analyzed, allowing for a more accurate determination of the melting point.