Burette Error Calculation
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Percentage Error Of 25cm3 Pipette
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Treatments MSDS Resources Applets General FAQ Uncertainty ChemLab Home Computing Uncertainties in Laboratory Data and Result This section considers the error and uncertainty in experimental measurements and calculated results. First, here are some fundamental things you should realize about uncertainty: • Every measurement has
Pipette Error
an uncertainty associated with it, unless it is an exact, counted integer, such as the uncertainty of measuring cylinder 100ml number of trials performed. • Every calculated result also has an uncertainty, related to the uncertainty in the measured data used to volumetric flask error calculate it. This uncertainty should be reported either as an explicit ± value or as an implicit uncertainty, by using the appropriate number of significant figures. • The numerical value of a "plus or minus" (±) uncertainty http://www.thestudentroom.co.uk/showthread.php?t=632126 value tells you the range of the result. For example a result reported as 1.23 ± 0.05 means that the experimenter has some degree of confidence that the true value falls in between 1.18 and 1.28. • When significant figures are used as an implicit way of indicating uncertainty, the last digit is considered uncertain. For example, a result reported as 1.23 implies a minimum uncertainty of ±0.01 and a range of 1.22 to https://www.dartmouth.edu/~chemlab/info/resources/uncertain.html 1.24. • For the purposes of General Chemistry lab, uncertainty values should only have one significant figure. It generally doesn't make sense to state an uncertainty any more precisely. To consider error and uncertainty in more detail, we begin with definitions of accuracy and precision. Then we will consider the types of errors possible in raw data, estimating the precision of raw data, and three different methods to determine the uncertainty in calculated results. Accuracy and Precision The accuracy of a set of observations is the difference between the average of the measured values and the true value of the observed quantity. The precision of a set of measurements is a measure of the range of values found, that is, of the reproducibility of the measurements. The relationship of accuracy and precision may be illustrated by the familiar example of firing a rifle at a target where the black dots below represent hits on the target: You can see that good precision does not necessarily imply good accuracy. However, if an instrument is well calibrated, the precision or reproducibility of the result is a good measure of its accuracy. Types of Error The error of an observation is the difference between the observation and the actual or true value of the quantity observed. Returning to our target analogy, error is
ERROR - Pawan Posted by Pawan on Dec 14, 2011 in Physical Chemistry | 1 comment Apparatus Errors Every time you make a measurement http://www.alevelhelp.com/2011/12/apparatus-error-experimental-error/ with a piece of apparatus, there is a small margin of error in that measurement due to the apparatus itself. For example, no balance can measure an exact mass but a very expensive and precise balance may be able to measure a mass to the nearest 0.0001 g, while a cheaper, less precise balance may only measure percentage error it to the nearest 0.1 g. Errors such as this are known as apparatus error and cannot be avoided, although they can be reduced by using the most precise equipment available. For example, when measuring out 25 cm3 of a solution, a pipette is much more precise than a measuring cylinder. When you do quantitative experiments (those percentage error of that require you to measure a quantity), you will have to calculate the total apparatus error from the sum of the apparatus error for each piece of equipment you use to make a measurement. Apparatus error for each piece of equipment = 100 x (margin of error)/(quantity measured) For example, imagine a pupil doing an experiment where she measured out 1.245 g of a base, make it up to 250 cm3 of solution in a volumetric flask, pipetted 25 cm3 of that solution into a conical flask, and then found that it reacted with 23.30 cm3 of acid in a titration using a burette. Balance (± 0.001 g) 100 x (0.001/1.245) = 0.08% Pipette (± 0.1 cm3) 100 x (0.1/25) = 0.40% Volumetric flask (± 0.1 cm3) 100 x (0.1/250) = 0.04% Burette (± 0.15 cm3) 100 x (0.15/23.30) = 0.64% Total apparatus error = 1.16% This means that the result of the experiment should be within 1.16% of the correct value. When you design experiments,