I did a lab about melting point. It is asking me for the purity of the compounds?
How do I find it?
Do I use melting points or percent yield?
How sharp the melting point is and how close to the accepeted melting point the value you find are indicators of how pure the sample might be. Thus a sharp melting point that agrees with the accepted value would indicate a high purity sample.
Even better would be to have a pure sample and the test sample together in the same apparatus, and if these melt at the same time then this is a good indicator that the test sample is pure.
Percentage yield is not a good indcator of purity. I have carried out many a reaction where the yield was low, say 30%, but the product was pure.
To determine the purity of a compound, you can use either melting points or percent yield, depending on the specifics of your lab experiment. Here's how you can use both methods:
1. Melting Point Method:
a. Measure the melting point of your compound using a melting point apparatus.
b. Compare the measured melting point to the known melting point range of the pure compound.
c. If the measured melting point falls within the known range, it indicates a high purity of the compound.
d. If the measured melting point significantly deviates from the known range, it suggests impurities in the compound.
2. Percent Yield Method:
a. Determine the theoretical yield of your compound, which is the maximum amount of pure compound that should have been synthesized based on stoichiometric calculations.
b. After synthesizing the compound, measure the actual yield obtained in your lab experiment.
c. Calculate the percent yield by dividing the actual yield by the theoretical yield and multiplying by 100.
d. A high percent yield (close to 100%) indicates a high purity of the compound, assuming the reaction is efficient and complete. Low percent yield suggests the presence of impurities or incomplete reaction.
Both methods can provide indications of compound purity, but they assess different aspects. Melting point method assesses the physical property of the compound, while percent yield method reflects the efficiency of the synthetic process. It's generally beneficial to use both methods for a comprehensive assessment of compound purity.
To determine the purity of a compound, both melting point and percent yield can be useful. Here's how you can use each of these factors to assess the purity of a compound:
1. Melting Point: The melting point of a pure compound is a characteristic property, meaning it should have a specific and well-defined melting point range. If your compound's melting point closely matches the literature value for the pure compound, it suggests a high level of purity. However, if your observed melting point range is broader or lower than expected, it indicates the presence of impurities.
2. Percent Yield: Percent yield is a measure of how much of the desired product is obtained compared to the theoretical yield. It gives you an idea of the efficiency of the reaction and the presence of impurities. If your percent yield is close to 100%, it suggests that the reaction was highly efficient and the compound is likely to be pure. On the other hand, a low percent yield indicates the presence of impurities or loss during the purification process.
So, both methods can provide information about the purity of a compound. It is recommended to use both melting point and percent yield to get a more comprehensive understanding of its purity. If the melting point is close to the literature value and the percent yield is high, it is a good indication of a pure compound. However, if the melting point deviates significantly from the expected value or the percent yield is low, further purification might be required to obtain a pure compound.