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CHM 2730, Exp 2 and 3: Comparison of Means, SP24
Due: 8:00 am, Tuesday, March 5th to the D2L Dropbox
Comparison of Means: Gravimetric and Volumetric Chloride Analyses Results
In this activity, you will assess whether the gravimetric and volumetric chloride methods
yielded results that are statistically the same or different in a manner analogous to lab
assignment 4.
Start by modifying the lab assignment 4 spreadsheet (make sure to do file → save as, as
save as your comparison of means assignment). Replace the given data with your
gravimetric and volumetric mass percentages from the corresponding results reports in
columns B and D, respectively, and change the data headings from method 1 and method
2 to gravimetric and volumetric:
1)
enter only the mass percentages that were utilized in the determination of the
average mass percent from each experiment (i.e. your final results)
2)
verify that the mass percentages you enter match those that are on the results
report PDF provided with your graded lab report
Complete the spreadsheet following the lab assignment 4 directions except step 7.
Reminders:
•
The method with the larger standard deviation is the numerator in the F calculation.
•
The method with the higher mean is variable 1 in the t calculations
Once you have completed the Excel document, you now have the information you need
for the narrative component of this exercise. Answer questions 1 and 2 listed below. Make
certain you point to the relevant information in the spreadsheet and its significance
Upload the spreadsheet (Excel file) and narrative (word or pdf file) to the corresponding
D2L dropbox by 8:00 am, Tuesday, March 5, 2024.
Compare the results for the gravimetric (Exp 2) and volumetric chloride (Exp 3) following
pages 74-76 (Harris). Upload the form to the corresponding D2L dropbox by the due date.
Upload a 1-page report addressing the following questions comparing Experiments 2
and 3 to the corresponding D2L dropbox by the due date. Be sure to use complete
sentences.
1.
Do both methods give the same (i.e. statistically equivalent) results?
2.
Do both methods have the same (i.e., statistically equivalent) precision?
Provide a coherent narrative to justify your answers to these questions, referencing data
on the comparative results sheet as necessary. Calculations (if necessary) can be
handwritten but not the narrative. In the narrative also discuss what you see as
advantages and disadvantages of the two methods used in Experiment 2 and Experiment
3, gravimetric and volumetric analysis. Which method do you think is more reliable, and
why?
Volumetric Cl- Titration Results
Fill-in all shaded cells, experimental data is entered in the darker shaded cells
Name:
Unknown Number:
%Cl- in Unknown (filled in by grader):
62.50%
Absolute error of %Cl- (raw grade based on this):
1.50%
Constants:
NaCl molar mass
Cl- molar mass
Stoichiometric ratio: Ag+/Cl-
58.44
35.45
1
Note 1: Include all data from all analyses. If an analysis is excluded from your results, report the experimental data but leave the corresponding calculated results cells
(lighter shading) blank.
Note 2: If entries are truncated by Excel to fewer decimal places than required, highlight the cell(s). On the HOME tab click the increase decimal icon on the number men to
increase the displayed number of decimal places as appropriate.
Standardization Titrations
NaCl mass (mg)
144.4
179.7
184.9
136.6
118.6
NaCl moles (mmol)*
2.47
3.07
3.17
2.336
2.021
AgNO3 moles (mmol)*
2.47
3.07
3.17
2.336
2.021
AgNO3 Volume (mL)
22.2
26
24.9
20
19.8
Average AgNO3 Molarity
AgNO3 Molarity (mmol/mL)
0.111
0.118
0.127
0.117
0.102
0.118 mmol/mL
Unknown Titrations
Unknown Mass (mg)
123.3
136.6
118.6
116
117
AgNO3 volume (mL)
18.2
20
19.8
18.2
20
Average AgNO3 Molarity
(mmol/mL)*
0.118
0.118
0.118
0.116
0.117
AgNO3 Moles (mmol)*
2.1456
2.36
2.3424
2.1072
2.34
Cl- moles (mmol)*
2.1456
2.36
2.3424
2.1072
2.34
Cl- Mass (mg)*
76.058
83.812
82.967
74.73464
82.953
Mass %Cl-^
61.66
61.38
69.97
60.57
60.68
Average Mass %Cl- in unknown^:
Standard Deviation Mass %Cl-:
0.64
0.0379
Confidence Interval Calculation
Confidence Level
n=
Degrees of freedom =
t=
95% Confidence Interval Mass % Cl- = +/-
95%
5.00
4.00
2.78
Interval
61.41%
to
66.59%
*report results to one more digit than allowed by applying the rules of significant figures, sf
^report (round) result to the correct number of sf by applying the rules of sf
Gravimetric Analysis Results Sheet
Fill-in all shaded cells, experimental data is entered in the darker shaded cells.
Name:
Unknown number:
Mass %Cl- in Unknown (filled in by grader):
62.21
Absolute error mass %Cl- (raw grade based on this):
0.135
Constants:
AgCl molar mass, g/mol
143.32
Cl molar mass, g/mol
35.45
Note 1: Include all data from all analyses. If an analysis is excluded from your results, report the experimental data but leave the corresponding calculated results cells
(lighter shading) blank.
Note 2: If entries are truncated by Excel to fewer decimal places than required, highlight the cell(s). On the HOME tab click the
increase decimal icon on the number men to increase the displayed number of decimal places as appropriate.
Sample #
1
2
3
4
Unknown Mass (mg)
169.9
214.5
201.0
193.4
AgCl Mass (mg)
882.5
964.1
889.6
894.2
Mass %Cl61.970
62.600
62.160
62.120
Average Mass %Cl- in unknown^:
Standard Deviation Mass %Cl-:
62.20
0.2720
Confidence Interval Calculation
Confidence Level
n=
Degrees of freedom =
t=
95% Confidence Interval Mass %Cl- = +/-
95%
4.00
3.00
2.78
0.40
Interval Range:
61.80
to
62.60
*report results to one more digit than allowed by applying the rules of significant figures, sf
^report (round) result to the correct number of sf by applying the rules of sf
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