Experiment 1 Lab Report PDF

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DUE Saturday April 7, 2018, 11:59 p.m.

CHEM 7L – Expt 1, SP18

Experiment 1 Lab Report: Precision and Accuracy Author: Daniela Fulginiti Date: 04-07-18 TA Name: Visha Jana This report should be 6 pages; you may delete instructions in red font. Do not adjust the margins, font sizes, etc. of this template. Save this document with filename Expt1_Author_TAname, where Author is your name, and TAname is your TA’s name.

ABSTRACT, including Accuracy: (12 pts) The majority of this section has been pre-written to serve as an example for future reports. Replace the blank regions with your content in blue. Watch significant figures (the temperature should be reported to the nearest 0.5 °C; standard deviations should have one or two sig figs). If there is a range or multiple values for temperature and density, indicate the range or values.

Three pieces of glassware (50-mL beaker, 10-mL graduated cylinder, and 10-mL volumetric pipet) were used to dispense 10 mL of water to evaluate the precision and accuracy of each type of glassware. The volume of dispensed water was determined by mass. The temperature of the water was 20°C, and the corresponding density at this temperature as indicated from a reference table was 0.99823 g/cm3. Three replicate measurements for each glassware were performed, and the averages, sample standard deviations, and percent relative standard deviation of an individual student were compared with analogous data from the entire laboratory section; these data are summarized below. Based on the laboratory section data, the most accurate piece of glassware was the volumetric pipet, and the most precise piece of glassware was the volumetric pipet.

Individual Trials (n = 3) Beaker: Avg ± stdev (ml) = 6.3 ± 0.3 ml Grad. Cyl: Avg ± stdev (ml) = 9.92 ± 0.13 ml Pipet: Avg ± stdev (ml) = 10.06 ± 0.12 ml

%RSD = 5.1 % %RSD = 1.3 % %RSD = 1.2 %

Collective Laboratory Section (n = 23) Beaker: Avg ± stdev (ml) = 8.1 ± 1.3 ml Grad. Cyl: Avg ± stdev (ml) = 9.9 ± 0.6 ml Pipet: Avg ± stdev (ml) = 9.98 ± 0.14 ml

%RSD = 16 % %RSD = 6.0 % %RSD = 1.4 %

Lab Report 1, Page 1

CHEM 7L – Expt 1, SP18

DUE Saturday April 7, 2018, 11:59 p.m.

EXPERIMENTAL: This section has been pre-written to serve as an example for future lab reports. If there were anomalies during the experiment (e.g. the balance was fluctuating, sample was spilled, etc.), describe them in the space below paragraph. If there were no anomalies, you may leave this space blank.

Glassware was cleaned with water and prepared for the experiments. Three glass vials with caps were rinsed with water and dried with a Kimwipe to remove residual water. Each vial and cap was labeled, and each pair of vial+cap was weighed using an analytical balance. Three pieces of glassware were also rinsed with water: a 50-mL beaker, a 10-mL graduated cylinder, and a 10-mL volumetric pipet. Approximately 100 mL of deionized water was placed in a beaker, and the temperature of the water was allowed to equilibrate until it was within 1 °C of the temperature of the room. The temperature was recorded using a thermometer. Once equilibrated, water was placed in the 50mL beaker up to the 10-mL mark, and this 10 mL of water was then poured into one of the preweighed glass vials. The vial was capped with the corresponding lid. This procedure was repeated two more times. Each of the three capped vials with water was weighed, and the mass was recorded. After the masses were recorded, the water was discarded, and the vials were dried. The same process was repeated with the 10-mL graduated cylinder, and with the 10-mL volumetric pipet. For the graduated cylinder, the meniscus was read at eye level. The three capped vials with water delivered from the graduated cylinder were individually weighed, and then emptied and dried for the final set of measurements with the pipet. For the volumetric pipet, a rubber bulb was used to draw water into the pipet, and the meniscus was read at eye level. The following anomalies occurred during the experiment:

Lab Report 1, Page 2

CHEM 7L – Expt 1, SP18

DUE Saturday April 7, 2018, 11:59 p.m.

Data: (6 pts) Fill in the table with your data (in blue). Watch significant figures (sig figs should be reported based on instrument and mathematical operations).

Beaker

Beaker, trial 1 Beaker, trial 2 Beaker, trial 3

20.0ºC Temperature of water (in ºC) Density of water at indicated temperature above (in g/mL) 0.99823 g/mL Mass of empty Mass of Dispensed Mass of H2O vial+cap (g) vial+cap with volume of (g) H2O (g) H2O (mL) 17.0694 g 23.4770 g 6.4076 g 6.4190 ml 16.9680 g 22.9330 g 5.9530 g 5.9636 ml 14.6810 g 21.2600 g 6.5790 g 6.5907 ml Beaker, average volume (mL) 6.3244 ml

Graduated Cylinder Temperature of water (in ºC) 20.0ºC Density of water at indicated temperature above (in g/mL) 0.99823 g/mL Mass of empty Mass of Dispensed Mass of H2O vial+cap (g) vial+cap with volume of (g) H2O (g) H2O (mL) 17.0718 g 27.0697 g 9.9979 g 10.0156 ml Gr. cylinder, trial 1 Gr. cylinder, trial 2 16.9559 g 26.9137 g 9.9578 g 9.9755 ml Gr. cylinder, trial 3 14.6806 g 24.4356 g 9.7550 g 9.7723 ml Graduated cylinder, average volume (mL) 9.9211 ml

Pipet

Pipet, trial 1 Pipet, trial 2 Pipet, trial 3

Temperature of water (in ºC) 20.0ºC Density of water at indicated temperature above (in g/mL) 0.99823 g/mL Mass of empty Mass of Dispensed Mass of H2O vial+cap (g) vial+cap with volume of (g) H2O (g) H2O (mL) 17.0713 g 27.0947 g 10.0234 g 10.0412 ml 16.9534 g 26.8919 g 9.9385 g 9.9561 ml 14.6727g 24.8414 g 10.1687 g 10.1867 ml Pipet, average volume (mL) 10.0613 ml

Lab Report 1, Page 3

DUE Saturday April 7, 2018, 11:59 p.m.

CHEM 7L – Expt 1, SP18

Calculations of standard deviation and %RSD: (6 pts) Show your calculations for the individual trials (not the collective laboratory values) for each piece of glassware. You must use equation editor. The formula for calculating these values is provided. Do not truncate values during the calculation, but report the final result correctly.

x i− ´x ¿ 2 ¿ ¿

s %RSD= ×100 ´x

N

¿ ∑ i=1 ¿ s= √ ¿

Beaker calculations for standard deviation and %RSD: s=

√

(6.4190 −6.3244 )2 +(5.9636 −6.3244 )2 +( 6.5907 −6.3244 )2 =0.3241 mL 2

%RSD=

0.3241 ×100=5.1246 % 6.3244

Percent Error:

10.0 −6.3 × 100=58.7 % 6.3

Beaker Stdev (correct number of sig. figs. based on Part 3 of manual): Stdev = 0.03 ml Beaker %RSD (two sig. figs.): %RSD = 5.1 %

Graduated cylinder calculations for standard deviation and %RSD:

s=

√

(10.0156−9.9211 )2+( 9.9755 −9.9211 )2 +(9.7723−9.9211 )2 =0.1304 mL 2

%RSD=

0.1304 ×100=1.3144 % 9.9211

Percent Error:

10.0 −9.9 × 100=1.01 % 9.9

Lab Report 1, Page 4

CHEM 7L – Expt 1, SP18

DUE Saturday April 7, 2018, 11:59 p.m.

Grad. cyl. Stdev (correct number of sig. figs. based on manual): Stdev = 0.13 ml Grad. cyl. %RSD (two sig. figs.): %RSD = 1.3 %

Pipet calculations for standard deviation and %RSD:

√

(10.0412−10.0613 )2 +( 9.9561−10.0613 )2+( 10.1867−10.0613)2 =0.1166 mL 2 0.1166 %RSD= ×100=1.1589 % 10.0613 s=

Percent Error:

10.0 −10.1 ×100=0.99 % 10.1

Pipet Stdev (correct number of sig. figs. based on manual): Stdev = 0.12 ml Pipet %RSD (two sig. figs.): %RSD = 1.2%

DISCUSSION: (6 pts) One paragraph: Restate the goal of the experiment, and summarize the results of the experiment, e.g. discuss your findings with respect to the accuracy and precision of the different pieces of glassware. Compare the average, sample standard deviation, and %RSD of your data with the larger data set from your entire section. What is the expectation when the number of sample trials increases? Our goal for this experiment was to identify the most accurate and precise glassware for measuring out 10 mL of water. In my data set I found that the pipet was both the most accurate and precise glassware. The pipet had the smallest percent error, 0.99%, meaning it is the most accurate of the three types of glassware. It also had the smallest standard deviation, 0.12 mL, and percent relative standard deviation, 1.2%, demonstrating that out of the three, this one was the most precise also. The graduated cylinder for my data did have numbers very close to the pipet’s data, but as we see with more trials in the class data, the graduated cylinder got farther from being the most precise and accurate, while the pipet maintained its position. For the beaker my average and standard deviation was 6.3 ± 0.3 ml and the classes’ average was 8.1 ± 1.3 ml. The class %RSD of 16% was much larger than my %RSD of 5.1%. The differences in these values helps show that the beaker is not precise and how everyone got very scattered results. My average for graduated cylinder was 9.92 ± 0.13 ml while the classes’ average was 9.9 ± 0.6 ml and my %RSD was 1.3%, while the classes’ was 6.0%. While the mean averages were very similar, the standard deviations were again a little different; this is expected since every person had different experiences and works differently with each glassware. For the pipet my average and standard deviation was 10.06 ± 0.12 ml with %RSD of 1.3%, while the classes’ was 9.98 ± 0.14 ml with %RSD of 1.2%. As the number of sample trials increases the greater it reflects the population mean, providing more significant and reliable results, thus we expect that as number of sample trials increase in our experiment the more accurate and reliable our data becomes. While normally we would expect the standard deviation to either decrease or stay the same as the number of trials increased, in this experiment it is normal for it to increase because each trial was done by a different person, and thus each person works with the glassware differently, producing variability. In the class data we also see Lab Report 1, Page 5

CHEM 7L – Expt 1, SP18

DUE Saturday April 7, 2018, 11:59 p.m.

that the pipet was both the most accurate and precise, validating my individual conclusion. It also demonstrates a bigger difference between the graduated cylinder and pipet which is expected as number of trials goes up.

Lab Report 1, Page 6...