Experiment 2: a Memo from Corporate Accuracy and Precision of “Volumetric” Glassware

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A MEMO FROM CORPORATE
Accuracy and Precision of “Volumetric” glassware
Jazet Nell Guimsop

Objectives:

In this laboratory experiment, the accuracy and precision of glassware made by a company manufacturing them will be assessed. This will be done by taking different volumes of water using a 10 mL graduated pipet, a 50 mL graduated buret, a 10 mL graduated cylinder, and a 50 mL graduated cylinder. After weighing each volume, we used the density of water at our room temperature to calculate the volume of each water samples. Then we compared that calculated volume (actual volume) to the one initially took; we used that result to assess the accuracy of our glassware by doing a t-Test. Also precision of the glassware was determined by calculating the standard deviation. At the end of this experiment, we expected our glassware to be accurate –corrected volume equal to zero; and precise – same volume obtained when the measurement is replicated.

Data:

We used a thermometer provided by our laboratory TA to get the water temperature which had a value of 22.3 ºC.

Table 1: Mass and Volume of Water delivered by a 10 mL graduated pipet

5mL| Mass of water (g)| Actual Vol (mL)| Corrected Vol| Trial #1| 4.9424| 4.9539| -0.046097|
Trial #2| 5.0299| 5.0416| 0.041607|
Trial #3| 5.0092| 5.0209| 0.020858|
10mL| | | |
Trial #1| 9.9410| 9.9641| -0.035863|
Trial #2| 9.9548| 9.9780| -0.022031|
Trial #3| 9.9310| 9.9541| -0.045887|

Table 2: Mass and Volume of Water delivered by a 50 mL graduated buret

5mL| Mass of water (g)| Actual Vol (mL)| Corrected Vol| Trial #1| 4.9896| 5.0012| 0.0012128|
Trial #2| 4.9802| 4.9918| -0.0082091|
Trial #3| 5.0298| 5.0415| 0.041506|
10mL| | | |
Trial #1| 9.8096| 9.8324| -0.16757|
Trial #2| 10.0204| 10.044| 0.0437215|
Trial #3| 9.9800| 10.003| 0.0032275|

Table 3: Mass and Volume Water of delivered by a 10 mL graduated cylinder

5mL| Mass of water (g)| Actual Vol (mL)| Corrected Vol| Trial #1| 4.8331| 4.8443| -0.15565|
Trial #2| 4.8634| 4.8747| -0.12528|
Trial #3| 4.7805| 4.7916| -0.20837|
10mL| | | |
Trial #1| 9.7118| 9.7344| -0.26560|
Trial #2| 9.6714| 9.6939| -0.30609|
Trial #3| 9.5302| 9.5524| -0.44762|

Table 4: Mass and Volume of Water delivered by a 50 mL graduated cylinder

5mL| Mass of water (g)| Actual Vol (mL)| Corrected Vol| Trial #1| 4.5994| 4.6101| -0.38990|
Trial #2| 4.6957| 4.7066| -0.29337|
Trial #3| 4.4917| 4.5022| -0.49785|
10mL| | | |
Trial #1| 9.5737| 9.5960| -0.40402|
Trial #2| 9.5005| 9.5226| -0.47739|
Trial #3| 9.6085| 9.6309| -0.36914|

Calculations:

The first volume metered out in each case was done as accurate as possible; we did consider errors but in our case, no determinate errors were observed while performing measurement. We then used a scale to record the mass of each volume measured. That mass and the density of will be used to calculate our actual volumes. At 22.3 ºC, the density of water is 0.99768 g/mL. The calculation of the volume for the first measurement of 5mL on a 10 mL graduated pipet is shown below:

v=mρ=4.59940.99768=4.6101

Equation 1: Sample calculation of water sample volume

We took an average from the volume dispensed on each of the three trials to calculate the standard deviation of the experiment. Excel sheet will be used to make the calculation rapidly; the formula used is shown below:

= 1ni=1nxi s=1ni=1n(xi-)2

Equation 2: Calculation for mean and standard deviation

Table 5: Average and error in Actual Volume (Calculated volume)

We now used a t.Test to compare each piece of glassware to one another; we wanted to see if the volumes collected, by each single glassware, were equal to one another. First we performed the F test on the two set of Data being compared, to see if they have similar Variance or not....
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