CHM 147 Oakland University Accuracy & Precision Department ofChemistry have low

Question

CHM 147 Oakland University Accuracy & Precision Department ofChemistry have low accuracy. An example of a systematic error that always generates masses is a balance that are 5 g lower than the true values Random errors do not produce a consistent deviation, instead the results will fluctuate above and below the true value. The size of the fluctuations produced by random error determines the precision of the measurement. The fluctuations produced by random error can also decrease the accuracy of a measurement; however, we expect that repeating a measurement many times dominated by random error and then calculating the mean result will increase the accuracy. This is because the positive and negative deviations caused by random error will end to cancel each other out when the mean is calculated. The standard error of the mean, Sm, is a statistic that is used to calculate the uncertainty (i.e., the size of the fluctuations) in a result that is the mean of N individual measurement. The Equation 2 is used to calculate Sm, where S is the standard deviation of the individual measurements calculated using Equation 1 (2) The uncertainty of the mean is dependent on the number of measurements, and Equation 2 tell us that the uncertainty of the mean decreases as we increase the number of measurements. In Part 1 of the experiment will use a bulls-eye approach to visualize precision and accuracy. The average distance from the target will represent the accuracy of the measurement, and the radius of the circle generated by the data points will represent how close or reproducible the measurements are. These are approximations for accuracy and precision. In Part 2, percent errors and standard deviations will be determined and used to investigate the precision and accuracy of the various glassware used in the lab. Part 3 will investigate the various propertie of the individual pieces of glassware Materials & Equipment 25 mL volumetric pipet 4 bean bags Pipet bulb Measuring tape or meter stick Buret reader 100 mL or 50 mL beaker Buret clamp 50 mL graduated cylinde Ring stand 25 mL volumetric flask Funnel 50 mL buret 20

Explanation / Answer

a)

Avoid:

beakers, since those are not calibrated for precise volume measurment

voluimetric flask, since it is TOO small, so 25 mL will not do

the buret is NOT used for liquid measurment

the pipet is small, so avoid it as well

So...

Use the 50 mL graduated cyklinder

b)

Use the graduated cylinder two time, add all volume to the 100 mL beaker

c)

Use the volumetric pipet, 25 mL TWICE, first measure either 20 mL and then 7.5 mL or 25 mL then 2.5 mL

d1)

The buret may be used to get hundreth accuracy, but typically used only in analytical chemistry experiment procedudures

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