Error Of 25cm3 Pipette
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error'). Experimental uncertainty arises because of: Limits in the how exact the measuring apparatus is. This is the precision of the apparatus. Imperfections in experimental procedures. Judgements uncertainty of measuring cylinder made by the operator. When can my results be said to be precise? percentage error of equipment If you repeat a measurement several times and obtain values that are close together, your results are said to be precise.
10cm3 Pipette Error
If the same person obtains these close values, then the experimental procedure is repeatable. If a number of different people carry out the same measuring procedure and the values are close the procedure is
100 Cm3 Measuring Cylinder Uncertainty
reproducible. What is a systematic error? A systematic error is one that is repeated in each measurement taken. If this is realised after the experimental work is done, it can be taken into account in any calculations. What are random errors? Even the most careful and experienced operator cannot avoid random errors. However, their effect can be reduced by carrying out a measurement many times (if the opportunity uncertainty of measuring cylinder 100ml exists) and working out an average value. Let's look in more detail at 'built-in' uncertainty of some laboratory equipment... Some measurement uncertainties are given below: EquipmentMeasurement to the nearest: Balance (1 decimal place)0.08 g Balance (2 decimal place)0.008 g Balance (3 decimal place)0.0008 g Measuring Cylinder (25 cm3)0.5 cm3 Graduated Pipette (25 cm3, Grade B)0.04 cm3 Burette (50 cm3, Grade B)0.08 cm3 Volumetric Flask (250 cm3, Grade B)0.2 cm3 Stopwatch (digital)0.01 s Calculating the percentage uncertainty (often called percentage error) ... Now try calculating the following percentage uncertainties... 1.00 g on a 2 decimal place balance 10.00 g on a 2 decimal place balance 1.00 g on a 3 decimal place balance 10 cm3 in a 25 cm3 measuring cylinder 25 cm3 in a 25 cm3 measuring cylinder 25 cm3 in a 25 cm3 graduated pipette (Grade B) 25 cm3 in a 50 cm3 burette (Grade B) 250 cm3 in a 250 cm3 volumetric flask (Grade B) 50 s on a digital stopwatch 8% 0.8% 0.08% 5% 2% 0.16% 0.32% 0.08% 0.02% Comparing uncertainties like those calculated above 'might' help you to decide which stage in an experimental procedure is likely to contribute most to the overall experimental uncertainty. How about thermometers..
ERROR - Pawan Posted by Pawan on Dec 14, 2011 in Physical Chemistry | 1 comment Apparatus Errors Every
10cm3 Measuring Cylinder
time you make a measurement with a piece of apparatus, 250cm3 measuring cylinder uncertainty there is a small margin of error in that measurement due to the apparatus itself. For percentage error of thermometer 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 http://www.avogadro.co.uk/miscellany/errors.htm g, while a cheaper, less precise balance may only measure 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, http://www.alevelhelp.com/2011/12/apparatus-error-experimental-error/ a pipette is much more precise than a measuring cylinder. When you do quantitative experiments (those 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 cm
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