CHEM 3401 Pre-Laboratory Assignment: Melting Points (Day Melting Point Experiment) Questions at the beginning of the lab period: 1. Reading Assignment from Nichols, 2nd Edition (Folio): Pages 307-323 – Recrystallization and Melting Point Experiments Laboratory Manual 2. What information is recorded from the melting point of a solid sample? 3. How much solid should be loaded into the melting point capillary tube? 2-3mm, loosely packed. 4. What part of the instrument is used to adjust the rate of heating on the Mel-TempR apparatus? 5. What data is noted and recorded to report the melting point for the unknown? 6. What is the appropriate procedure to use if you are not sure what the melting point is for your sample? Begin your answer with melting point sample preparation.
The Correct Answer and Explanation is:
2. What information is recorded from the melting point of a solid sample?
The melting point range is recorded. This includes the temperature at which the sample first begins to melt and the temperature at which the sample is completely liquefied.
3. How much solid should be loaded into the melting point capillary tube?
About 2 to 3 millimeters of the solid should be loaded into the capillary tube. The sample should be loosely packed to ensure even heat distribution and accurate results.
4. What part of the instrument is used to adjust the rate of heating on the Mel-TempR apparatus?
The rate of heating is adjusted using the power or temperature control knob on the Mel-TempR apparatus. This control allows the user to increase or decrease the heating rate depending on the sample and desired precision.
5. What data is noted and recorded to report the melting point for the unknown?
The beginning and end temperatures of the melting range are noted. These two values define the melting point range of the unknown sample. A narrow range typically indicates high purity, while a broader range suggests impurities.
6. What is the appropriate procedure to use if you are not sure what the melting point is for your sample?
Melting point sample preparation involves first finely pulverizing the dry sample, then filling a capillary tube to a height of about 2 to 3 millimeters. If the melting point is unknown, begin by performing a rapid heating trial. Heat the sample quickly while observing closely to estimate the general melting range. Once a rough idea of the melting point is obtained, allow the apparatus to cool. Reload a fresh sample into a new capillary tube and reheat slowly, about 1 to 2 degrees Celsius per minute, starting approximately 10 to 15 degrees below the estimated melting point. This slow heating provides a more accurate and reliable measurement of the melting range. Always record both the starting and ending temperatures for complete data.
