101 - C - Uncertainty in Measurements in Chemistry - Report PDF

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C-15

Report: Uncertainty in Measurements

Assessment Report

Mangune, Margarette Name: ____________________________ Bench #_______ X13L October 14, 2020 Section: ___________ Date: _________________________ Lioudmila Badalova Laboratory Instructor: ___________________________

/10 Deductions Total

/10

Parts A, B, and C

1. Using data from your first measurement with the 20 mL beaker, show your calculations to determine the following values. Note: you only need to show one calculation in full for each part. Be sure to include units! a. The mass of the dispensed solution: (0.25)

Mass of the dispensed solution: Mass of capped vial and solution – Initial mass of capped empty vial 24.953g – 16.140g = 8.813g

b. The density of the NaCl (aq) solution: (0.5)

Density = M/V Mass of dispensed solution: 8.813 g Volume of solution: 10 mL

= 8.813/10 =0.88 g/mL

C-16 c. Complete the following table for the three pieces of glassware. Express your densities to 4 decimal places for now. (0.5) Trial #

Solution Volume (mL)

1 20 mL Beaker

2 3 4 1

10 mL Graduated Cylinder

2 3 4 1

10 mL Volumetric Pipet

2 3 4

Solution Mass (g)

Solution Density (g/mL)

10 mL

8.813 g

10 mL

9.137 g

10 mL

9.253 g

0.9253 g/mL

10 mL

9.120 g

0.9120 g/mL

10 mL

9.981 g

0.9981 g/mL

10 mL

9.874 g

0.9874 g/mL

10 mL

9.779 g

0.9779 g/mL

10 mL

9.904 g

0.9904 g/mL

10 mL

10.026 g

1.0026 g/mL

10 mL

10.028 g

1.0028 g/mL

10 mL

10.021 g

1.0021 g/mL

10 mL

10.025 g

1.0025 g/mL

0.8813 g/mL 0.9137 g/mL

2. Using the four trials for the 20 mL beaker, show your calculations to determine the following values. Be sure to include units! a. The mean density of the NaCl (aq) solution: (0.75) Mean of density: 0.8813 + 0.9137 + 0.9253 + 0.9120 =3.6323/4 =0.9081g/mL

b. The standard deviation of the density of the NaCl (aq) solution, rounded to the correct number of significant figures: (0.75) Standard Deviation:

√

2

2

2

2

(0.8813−0.9081) +(0.9137 −0.9081 ) +(0.9253−0.9081) +(0.9120−0.9081 0.0188 g/mL) 4−1

=

c. Complete the table below for all of the pieces of glassware. Use the correct number of decimal places (and thus significant figures) in the mean density. (0.5)

C-17

Mean Density (g/mL)

Uncertainty for the Density (g/mL)

20 mL Beaker

0.9081g/mL

±0.02g/mL

10 mL Graduated cylinder

0.9080g/mL

±0.02g/mL

10 mL Pipet

1.0025g/mL

± 0.0003g/mL

3. Using the given density for the NaCl (aq) solution, determine which piece of glassware

(beaker, graduated cylinder, or pipette) yielded the most accurate measurements. Base your answer on your own results. Explain your answer, and indicate whether or not your results are consistent with the expectations for each piece of glassware. (0.75) -

The true given density of the solution is 1. 024g/mL and when you subtract it to the mean density of each glassware the most accurate value was the 10 mL pipet with only a difference of 0.0215g/mL. While the least accurate value is the 20 mL beaker with 0.1159g/mL difference.

4. Of the beaker, graduated cylinder, and pipette, which one exhibited the best precision? Base your answer on your own results. Explain your answer, and indicate whether or not your results are consistent with the expectations for each piece of glassware. (0.75) -

The most precise out of all three is the pipette- with only a 0.0007 difference in its highest and lowest value of the mass.

-

The beaker has an expected percent relative uncertainty of ± 5% and its result is ± 2% which was lower than expected.

-

The graduated cylinder has an expected tolerance of ± 0.05 mL and the result was ±0.02 mL which is lower than expected.

-

The pipette has an expected tolerance of ± 0.0 mL and the result was ±0.0003 mL which is lower than expected

C-18 5. Based on your data, did any of the pieces of glassware exhibit systematic error? Explain. (0.5) -

Yes, the beaker was not precise with the value that was obtain

6. Based on the data obtained for the 20 mL beaker, is it necessary (or proper) to report four digits in the answer? Explain why or why not? (0.5)

-

No, the value that was obtained had a great difference so even if you deduct the digits you can still notice the variation of its error.

C-19 Part D 7. Employing the volumes and masses acquired in Part D of the experiment, with the burette, prepare a plot of mass versus volume using a spreadsheet program such as Google Sheets. Your instructor will have demonstrated the use of Google Sheets, and some brief instructions are available starting on page 30 of the introductory section of the lab manual. Print and submit your plot along with this report. (2.0)    

Plot mass on the y-axis, and volume on the x-axis Remember to label both axes and indicate units Include a short but descriptive title for your plot Include a best-fit line (trendline) for your data

De t e r mi na t i onofDe ns i t yus i n gBur e t t e 9 8

f ( x)=1. 04x−0 . 04

Ma s sofSol u t i on( g)

7 6 5 4 3 2 1 0 1

2

3

4

5

6

7

8

Vol u meofs ol ut i o n( mL)

8. Using the graph and best-fit line prepared in Question 7 to complete the following: a. Write out the equation (in the form y = mx + b) for the best-fit line. (0.25) -

y = 1.0353x - 0.0379

9

C-20 b. What is the value for the slope of the best-fit line generated by the spreadsheet software? Don’t forget to include units. (0.25) -

Slope= 1.0353g/mL

c. To which physical property of the salt solution does this slope correspond? (0.25)

-

Density

d. What is the value for the y-intercept of your best-fit line? Include units. (0.25) -

Y intercept= 0.0379 mL

e. Your y-intercept should have a value very close to 0 g. Explain why this is so. (0.25) End of Report

It is the run/ change of the line...