uncertaintities

uncertaintities - Errors and uncertainties in chemistry...

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Errors and uncertainties in chemistry internal assessment The consideration and appreciation of the significance of the concepts of errors and uncertainties helps to develop skills of inquiry and thinking that are not only relevant to the group 4 experimental sciences. The evaluation of the reliability of the data upon which conclusions can be drawn is at the heart of a wider scientific method that IB students consider in other areas such as group 3 individuals and societies, and theory of knowledge. They then may apply this in their subsequent educational, professional and personal lives. Errors and uncertainties are addressed in “Topic 11: Measurement and data processing” of the subject guide and this topic can be very effectively treated through the practical scheme of work. The treatment of errors and uncertainties is directly relevant in the internal assessment criteria of: data collection and processing, aspects 1 and 3 (recording raw data and presenting processed data) conclusion and evaluation, aspects 1, 2 and 3 (concluding, evaluating procedure(s), and improving the investigation). Expectations at standard level and higher level The expectations with respect to errors and uncertainties in internal assessment are the same for both standard and higher level students and are supported by topic 11 of the subject guide. Within internal assessment students should be able to do the following: make a quantitative record of uncertainty range (±) (data collection and processing: aspect 1) state the results of calculations to the appropriate number of significant figures. The number of significant figures in any answer should reflect the number of significant figures in the given data (data collection and processing: aspect 3). propagate uncertainties through a calculation so as to determine the uncertainties in calculated results and to state them as absolute and/or percentage uncertainties (this applies to both higher and standard level students). Only a simple treatment is required. For functions such as addition and subtraction absolute uncertainties can be added. For multiplication, division and powers, percentage uncertainties can be added. If one uncertainty is much larger than others, the approximate uncertainty in the calculated result can be taken as due to that quantity alone (data collection and processing: aspect 3). determine from graphs physical quantities (with units) by measuring and interpreting a slope (gradient) or intercept. When constructing graphs from experimental data, students should make an appropriate choice of axes and scale, and the plotting of points should be clear and accurate. (Millimetre square graph paper or software is appropriate. Quantitative measurements should not be made from sketch graphs.) The uncertainty requirement can be satisfied by drawing best-fit curves or straight lines through data points on the graph (data collection and processing: aspect 3). (Note: Chemistry students at SL and HL are not expected to construct uncertainty
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This note was uploaded on 01/21/2011 for the course CHEM 1 taught by Professor Ram during the Spring '10 term at Oxford University.

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uncertaintities - Errors and uncertainties in chemistry...

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