Chemical Forums
Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: spirochete on June 10, 2013, 01:22:41 PM
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A Class A 50 mL buret is said to have a tolerance of ±0.05 mL. Yet it is typically said that a Class A 50 mL buret can be read to ±0.01 mL.
How can both of these things be true at the same time?
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I would assume because "tolerance" and "what it can be read to" each have a definition that is likely similar to, but not the same as, each other. And very possibly neither is a synonym for "accuracy." What can you pull together from textbook definitions for each term?
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It is not different from having a voltmeter that shows 3 digits, but is known to have accuracy ±5%. Just because it displays something, doesn't mean it is right, right?
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I'm still confused how he can read it to 0.01 ml.
That'd mean every ml range was sub-divided 100 times. That'd need 5000 marks on the 50 ml burette.
Something doesn't make sense.
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Unfortunately I can't look up "can be read to" in a glossary. As for tolerance, it's defined as "manufacturer's stated uncertainty in the accuracy of a device. . ."
So tolerance is clearly an uncertainty in accuracy. I believe that reading a buret to ±whatever is an indication of the precision to which it can be read. So probably this is just a classic case of accuracy vs. precision that they teach you about in the first ten minutes of gen chem. I feel silly now. Thank you for your helpful comments.
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Don't feel bad. I'm always pointing the precision/accuracy dichotomy out, and then I went and screwed it up myself this morning. http://www.chemicalforums.com/index.php?topic=68895.msg248209#msg248209