Trouble finding where I went wrong calculating concentration

I should have had 10^6 µM. After comparing with another student's calculations, it seems that my final concentration was incorrect and I may have used the incorrect units (µL instead of mL). I have discussed this with my tutor, who pointed out the discrepancy, and have made adjustments to my calculations. However, I am still unsure of where the number 73.6 came from in my original calculations. In summary, the conversation involves a student discussing their incorrect calculations for stock and final concentrations of Glycerol in a laboratory class. They have compared their results with another student and have made adjustments, but are unsure of where the error originated from.
  • #1
Trufflehog
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In our laboratory class we were required to calculate the stock (mM) and final (µM) concentrations for Glycerol. The tutor said my final calculations were incorrect and that I had made an error. He didn't have enough time show me where I went wrong. I have compared my results with another student who was told their calculations were correct.
Results.png


I have expanded my calculations to try and identify the problem but I cannot see where I am going wrong. Is there an error in my calculations?
Caclulations.png
 
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  • #2
Your calculations look OK to me, except the very last step. 1M is not 109µmol. What is it?
I wonder if the "25" and "540" should have been mL, not µL. Certainly, 3.65 µL in 25 µL (or 3.65 mL in 25 mL, or L in L..) is quite a high concentration; of the order of 2M sounds the right ballpark, even without doing any calculations. I can't see where the number 73.6 comes from.
 
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  • #3
Thanks for noticing the error where I should of had 10^6 µM. Yeah we definitely used µL for all those solutions in the lab. I had discussed it with the tutor and all he said was that my answers did not match his. He did however tell me that another student got the correct answers and I was able to copy those down. I thought maybe it's possible that my tutor got the incorrect result but if I were to challenge that I thought I'd check with someone else calculations first.

Thanks mjc123
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1. Why am I having trouble finding where I went wrong in my concentration calculation?

There could be several reasons for this difficulty. It's possible that you made a mistake in your calculations or used incorrect data. It's also possible that your equipment or measuring tools were not calibrated properly. Additionally, there may be external factors that affected your results, such as temperature or human error.

2. How can I check my calculations for errors?

One way to check your calculations is to redo them step by step, making sure to double check each step and using a calculator or other tools to assist. Another method is to have a colleague or lab partner review your work and see if they spot any mistakes or discrepancies.

3. What should I do if I can't find a mistake in my calculations?

If you've gone through your calculations multiple times and still can't find where you went wrong, it's best to consult with a more experienced scientist or your supervisor. They may be able to offer insight or suggest alternative methods for checking your work.

4. How can I prevent this issue from happening in the future?

To avoid having trouble finding mistakes in your concentration calculations, it's important to be diligent and thorough in your work. Take your time and double check your work at each step. It's also helpful to label and organize your data clearly, and to use reliable and calibrated equipment.

5. Is it common to have difficulty finding errors in concentration calculations?

Yes, it's very common for scientists to make mistakes in their calculations, especially when dealing with complex equations or large amounts of data. It's important not to get discouraged and to continue to review and double check your work to ensure accurate results.

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