Three students (Saerom, Hayoung, and Jiwon) are asked to determine the ppm Ca in a drinking water sample by titration with EDTA. Each student performed five trials for the sample. The results in ppm Ca are the following:
Three students (Saerom, Hayoung, and Jiwon) are asked to determine the ppm Ca in a drinking water sample by titration with EDTA. Each student performed five trials for the sample. The results in ppm Ca are the following:
Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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Transcribed Image Text:Write your complete solutions on yellow paper, round your answers to the appropriate number of
significant figures, and box the final answer. The deadline for submission is at the end of the class.
Note: You do not need to write your solutions for the items that can be derived from your
calculators.
1. Three students (Saerom, Hayoung, and Jiwon) are asked to determine the ppm Ca in a drinking
water sample by titration with EDTA. Each student performed five trials for the sample. The results in
ppm Ca are the following:
Saerom
Hayoung
Jiwon
a. Get the mean, SD, and % RSD of each student's results.
b. If the true value is 35 ppm, calculate the relative error of each student's results.
c. Comment on the precision and accuracy of each student's results. The maximum % RSD and
the relative error set by the lab is 5.0%.
d. Use the following table to summarize your answers.
Mean
SD
%RSD
Relative Error
Comment
31, 32, 33, 33, 32
35, 34, 34, 35, 34
35, 38, 33, 35, 37
Saerom
Mean
SD
95% CI
Hayoung
2. Consider the following sets of replicate measurements:
Set B
Set A
70.14 mL
2.9 g
3.2 g
69.99 mL
70.12 mL
2.6 g
71.51 mL
3.1 g
2.8 g
Jiwon
a. Calculate the mean, SD, and confidence interval at 95% confidence level for each of the three
sets. Use the following table to summarize your results.
Set A
Set B
Set C
0.314 mg
0.320 mg
0.317 mg
0.319 mg
0.315 mg
0.326 mg
Set C
Transcribed Image Text:b. In set C, the last value is suspected to be an outlier. Should it be rejected?
3. Jisun needs to prepare a 0.1000 M Na2S2O3 titrant for the iodometric analysis of commercial bleach
samples. Calculate the mass of Na₂S₂O3.5H₂O (in g); she needs to prepare 500.0 mL of the titrant
solution. The molecular weight of Na2S₂O3.5H₂O is 248.18 g mol¹¹.
4. Seoyeon needs to prepare a 10.0% (w/w) H₂SO4 solution for the analysis of a certain drug sample.
Calculate the volume of concentrated H₂SO4 (in mL); she needs to prepare 250.0 mL of the solution.
The concentrated H₂SO4 found in the laboratory is 98.0% (w/w) pure.
5. Chaeyoung needs to prepare a 0.1000 M HCI titrant for the analysis of the carbonate content of a
rock sample. Calculate the volume of concentrated HCI (in mL); she needs to prepare 1.00 L of the
titrant. The concentrated HCI found in the laboratory is 36.0% (w/w) pure and the density is 1.18 g
mL¹. The molecular weight of HCI is 36.46 g mol¹¹.
Table A.2 The +-distribution
Value of t for a confidence interval of
Critical value of It for P values of
number of degrees of freedom
1
2
3
5
8
9
10
12
14
16
18
20
30
50
90%
0.10
3
4
5
6.31
2.92
2.35
9
10
2.13
2.02
1.94
1.89
1.86
1.83
1.81
1.78
1.76
1.75
1.73
1.72
1.70
1.68
1.64
95%
0.05
12.71
4.30
3.18
2.78
2.57
2.45
2.36
2.31
2.26
2.23
2.18
2.14
2.12
2.10
2.09
2.04
2.01
1.96
98%
0.02
Table A.5 Critical values of G (P = 0.05)
for a two-sided test
Sample size
31.82
6.96
4.54
Critical value
1.155
1.481
1.715
1.887
2.020
2.126
2.215
2.290
3.75
3.36
3.14
3.00
2.90
2.82
2.76
2.68
2.62
2.58
2.55
2.53
2.46
2.40
2.33
99%
0.01
The critical values of It are appropriate for a two-tailed test. For a one-tailed test the value is
taken from the column for twice the desired P-value, e.g. for a one-tailed test, P = 0.05, 5
degrees of freedom, the critical value is read from the P = 0.10 column and is equal to 2.02.
Taken from Barnett, V. and Lewis, T., 1984,
Outliers in Statistical Data, 2nd edn,
John Wiley & Sons Limited.
63.66
9.92
5.84
4.60
4.03
3.71
3.50
3.36
3.25
3.17
3.05
2.98
2.92
2.88
2.85
2.75
2.68
2.58
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