CHEM 1&2 Lab Manual & worksheets pg 227

CHEM 1&2 Lab Manual & worksheets pg 227 - Basic...

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Basic Laboratory Statistics General Chemistry I and II Lab Manual Dakota State University page 227 of 232 just the mass of the liquid, this systematic error will automatically cancel itself. However, it is important to note that this error cancellation will only occur if we are consistent with the instruments that we use since it is highly unlikely that a second instrument, in this case a balance, will be off by the same amount as the other. Thus, if we switch balances in the middle of the experiment, these systematic errors will not cancel out. “Accuracy” is how close the mean is to the true value (which may or may not be known). For example, because of the density of water, 100.00 mL of water should have a mass of 100.00 g. You can have high accuracy with low precision. For example, suppose our balance is outside on a gusty day; we might get five readings of 95.02, 107.80, 96.42, 101.33 and 99.46. The mean of this data (see below) is 100.01 g, which is very close to what it ought to be, but the values themselves are all over the place. Naturally, we want results that are both accurate and precise.
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This note was uploaded on 01/27/2012 for the course CHM 2045 taught by Professor Josephwalter during the Fall '11 term at Dakota State.

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