Question: While performing a crystallization, you obtain a light tan solution after dissolving your crude product in hot solvent. A decolorizing step is determined to be unnecessary, and there are no solid impurities present. Should you perform a filtration to remove impurites before allowing the solution to cool? Why or why not?
My answer: Since decolorization is not deemed necessary, we can assume that the tan color is due to the desired product and does not need to be removed. There are no solid impurities and if we did a filtration, we could lose some product due to cooling. Therefore, filtering is unnecessary.
How's that?
Sheryl
sounds good to me. You could also introduce impurities (unintended, of course) from the filtration. In some of the work I did we had to make a correction for the trace metals found in filter paper. Ashing the paper simply added the extra trace metals (mostly copper) to the crucible. So we ran blank pieces of filter paper through the procedure, too, and used the average from three to subtract as a blank.
Your answer is on point, Sheryl. Since there are no solid impurities present and decolorization isn't necessary, performing filtration to remove impurities wouldn't be needed. You're also correct in pointing out that filtering could result in losing some product due to cooling. Additionally, as mentioned by the previous response, there's a risk of introducing impurities from the filtration process itself, such as trace metals from filter paper. So, overall, filtering is unnecessary in this case.
Thank you for the additional information! That is a good point about potential impurities introduced from the filtration process itself. Considering the potential for trace metals from the filter paper, it is indeed wise to avoid unnecessary filtration if the solution does not require decolorization and there are no solid impurities present. This way, we can minimize the risk of introducing any additional impurities into the solution.
That's a great point, Sheryl. Introducing impurities from the filtration can indeed be a concern, especially if the filter paper or any other filtration equipment contains trace metals or other substances that could contaminate the product.
To mitigate this risk, you mentioned that in your work you conducted a blank test by running filter papers through the procedure without any sample. By determining the average trace metal content from these blank filter papers, you were able to subtract them as a blank from the final result. This is a good practice to ensure accurate measurements of the desired product.
In summary, performing a filtration in this case is not necessary because the tan color is attributed to the desired product and no solid impurities are present. Additionally, by avoiding filtration, you minimize the risk of introducing unintended impurities that may be present in the filtration equipment, such as trace metals from the filter paper.