Questions and Answers
How do you calculate the percent error of an obtained melting point range?
Take the average of the observed melting point range and the average from literature, then use %error = (observed - expected) / expected x 100.
How do you analyze percent error of melting points?
An acceptable range is usually 5% or less; greater than 5% suggests impurities exist in the sample.
What was the objective of the melting point lab?
Identify an unknown based on its melting point and confirm identity with a mixed melting point experiment.
What did we do in the melting point lab?
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Excess unknown solid goes in ___________________.
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Capillary tubes with solid inside and rinsed tubes go in ______________.
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Melting points are usually reported as _______.
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If you observe a melting point 15 °C lower than the reported literature value, the cause of this may be ______.
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True or False: All molecules have a melting point.
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True or False: To measure a melting point accurately, a large quantity of material (>100 mg) is required.
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When measuring a melting point, you should _______ as you approach the expected melting point.
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Study Notes
Melting Point Experiment Key Concepts
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Percent Error Calculation
- Average the observed melting point range by summing the values and dividing by the count.
- Average the literature melting point range.
- Use the formula: %error = (observed - expected) / expected x 100.
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Analyzing Percent Error
- Acceptable percent error is typically 5% or less.
- Percent error greater than 5% indicates potential impurities in the sample.
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Objective of the Lab
- Determine the identity of an unknown compound based on its melting point.
- Confirm the identified compound using a mixed melting point experiment.
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Lab Procedure Overview
- Conducted a fast and slow run to evaluate the unknown compound.
- Selected compounds from the shelf for mixtures to observe melting point behavior.
- Identified unknown by examining which melting point range was depressed and widened.
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Waste Disposal Protocols
- Excess unknown solid should be disposed of in the Solid Organic Waste Container.
- Capillary tubes containing solid and rinsed tubes must go into the Broken Glass container.
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Melting Point Reporting
- Melting points are reported as ranges rather than single values.
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Interpreting Large Melting Point Deviations
- A melting point observed to be 15 °C lower than literature values suggests:
- Possible impurities or residual solvent.
- Alternatively, isolation of a different compound.
- Both possibilities are valid.
- A melting point observed to be 15 °C lower than literature values suggests:
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Melting Point Characteristics
- Not all molecules possess a melting point.
- Accurate melting point measurement does not require large quantities (>100 mg) of the sample.
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Measuring Melting Points
- As the expected melting point is approached, it’s important to:
- Pay close attention and note the temperature at the onset of melting.
- Decrease the rate of heating for more precise melting point measurements.
- As the expected melting point is approached, it’s important to:
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Description
Test your knowledge on calculating and analyzing percent error in melting point experiments. This quiz will cover key concepts related to melting point ranges and the mathematical formulations needed to determine accuracy in laboratory settings.
