www.mindbites.com In this lesson, Prof. Yee discusses precision and accuracy in measurements. He explains that all measurements will have a degree of uncertainty due to instrumentation, and the range of uncertainty will appear in the last digit of the measurement. You want to have measurements that are both precise and accurate. Precision is the reproducibility of the measurement of a quantity and is tied to the concept of random error. Prof. Yee uses a ruler as an example of precision. Accuracy refers to how close a measurement is to a hypothetical true value. It is possible for a measurement to be precise but not accurate if there is a systematic error. Systematic error is an error inherent to the measurement of a value, such as a clock that is consistently 5 minutes fast. Finally, Prof. Yee explains the relationship between precision and accuracy using a game of darts. Taught by Professor Yee, this lesson was selected from a broader, comprehensive course, Chemistry. This course and others are available from Thinkwell, Inc. The full course can be found at www.thinkwell.com The full course covers atoms, molecules and ions, stoichiometry, reactions in aqueous solutions, gases, thermochemistry, Modern Atomic Theory, electron configurations, periodicity, chemical bonding, molecular geometry, bonding theory, oxidation-reduction reactions, condensed phases, solution properties, kinetics, acids and bases, organic reactions, thermodynamics, nuclear chemistry, metals, nonmetals …
Chemistry: Precision and Accuracy
A comparison of methods to determine the biodegradable dissolved
Product Description
This digital document is a journal article from Soil Biology and Biochemistry, published by Elsevier in 2006. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.
Description:
The importance of dissolved organic matter (DOM) in many soil processes is determined in large part by its availability to microbial uptake and decomposition, as this biodegradation can yield both energy and limiting nutrients. Despite its importance in soil ecology, there are no standard approaches to measuring the biodegradable fraction of DOC (BDOC) in soils. Here, we evaluate the comparability and reproducibility of methods employed in six laboratories including batch, kinetic, and bioreactor methods. Solutions from a variety of sources (throughfall, soil solution and soil extracts) were analysed using methods typically employed in each of the six participating laboratories. Our results show that the precision of various BDOC methods was similar (5-15%) across a broad range of BDOC (from 12% to 56% of total DOC). Differences in mean BDOC for the various test solutions were statistically significant when results were pooled across all the methods, and only a 90-day incubation resulted in consistently higher values for BDOC than the other methods. For 4 of 6 test solutions, measured BDOC increased by 6-13% with added nutrients. Current methods produce largely comparable results, providing the justification for comparisons among existing data sets collected with different methodologies. We recommend two standard methods for future studies: (1) a rapid determination of relatively labile DOC (measurement of DOC removal after 7 days of incubation with added nutrients) and (2) a 42-day incubation with repeated analysis of CO”2 production when determination of decomposition rate constants and a labile and relatively refractory component of DOC is desired.
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