Experiment 1: Mixed Melting Points
ABSTRACT
Determining the melting point of a solid organic compound is the easiest way to identify the compound and determine its purity at the same time. For actual samples of compounds, the melting will occur over a range of temperatures making the melting points into a melting “range”. The difference between the temperature at which the sample begins to melt and the temperature at which it finishes melting, or the magnitude of the melting range, is a very important criteria of determining the purity. The smaller the melting range and the closer the experimental value is to the reported melting point, the purer the sample is. Since many compounds have similar melting points, a mixed melting point can be taken by mixing samples of the unknown with an authentic sample of the known compound and taken the melting point of the mixture. In this experiment, unknown #26 had a melting range of 154°-155°C. After looking at known melting points, we expected the unknown to be citric acid. While determining the melting point of the authentic citric acid sample, we got a melting range of 153°-160°C. The melting range of the mixed sample, unknown and authentic citric acid, was 151°-154°C, proving our hypothesis correct.
RESULTS
Unknown #26
Melting range of unknown: 154° - 155°
Melting range of citric acid: 153° - 160°
Melting range of mixed citric acid & unknown: 151° - 154°
Unknown #26 is Citric Acid
All structures look similar by observation and there was no color change in any of the samples.
Structural Formula of Citric Acid:
QUESTIONS
1. Colligative property depends on the number of molecules, not the type of molecule. Another colligative property instead of freezing point depression and boiling point elevation is osmotic pressure.
2. A melting range should always be reported because it tells you if your compound is pure or not. If the melting range is over 10°C of your authentic sample, than the compound is not pure.
3. If the compound were A,
Determining the melting point of a solid organic compound is the easiest way to identify the compound and determine its purity at the same time. For actual samples of compounds, the melting will occur over a range of temperatures making the melting points into a melting “range”. The difference between the temperature at which the sample begins to melt and the temperature at which it finishes melting, or the magnitude of the melting range, is a very important criteria of determining the purity. The smaller the melting range and the closer the experimental value is to the reported melting point, the purer the sample is. Since many compounds have similar melting points, a mixed melting point can be taken by mixing samples of the unknown with an authentic sample of the known compound and taken the melting point of the mixture. In this experiment, unknown #26 had a melting range of 154°-155°C. After looking at known melting points, we expected the unknown to be citric acid. While determining the melting point of the authentic citric acid sample, we got a melting range of 153°-160°C. The melting range of the mixed sample, unknown and authentic citric acid, was 151°-154°C, proving our hypothesis correct.
RESULTS
Unknown #26
Melting range of unknown: 154° - 155°
Melting range of citric acid: 153° - 160°
Melting range of mixed citric acid & unknown: 151° - 154°
Unknown #26 is Citric Acid
All structures look similar by observation and there was no color change in any of the samples.
Structural Formula of Citric Acid:
QUESTIONS
1. Colligative property depends on the number of molecules, not the type of molecule. Another colligative property instead of freezing point depression and boiling point elevation is osmotic pressure.
2. A melting range should always be reported because it tells you if your compound is pure or not. If the melting range is over 10°C of your authentic sample, than the compound is not pure.
3. If the compound were A,