As part of an analytical chemistry laboratory course, a student measured the Cac

Question

As part of an analytical chemistry laboratory course, a student measured the Cacontent in two water samples, city-supplied drinking water and well-supplied drinking water, using two different analytical methods, flame atomic absorption spectrometry (FAAS) and EDTA complexometric titration. The results of this experiment are shown below as the mean Ca2+ concentration (x) ± standard deviation (s) in units of parts per million (ppm). Each sample was measured five times (n 5) by each method. I | Well-Supplied Drinking Water (x± s) City-Supplied Drinking Water(s) 58.14 ± 0.66 ppm 58.89 ± 0.95 ppm FAAS 63.33 ± 0.68 ppm EDTA Titration 64.18 ± 0.97 ppm Method Comparison: For each drinking water sample (city and well), compare the Ca2 content measured with FAAS and EDTA titration. Calculate the t value (toe) aty: for each sample. Do the methods produce statistically different results at the 95% confidence level when measuring the Ca2 conte ofthe two drinking water samples (Yes or No)? A list of Student's t Well A) Number O Yes rak- Number Yes values at several confidence levels can be found in the Student's ttable

Explanation / Answer

for city

Two-Sample T-Test and CI

Sample N    Mean StDev SE Mean
1       5 58.140 0.660     0.30
2       5 58.890 0.950     0.42

Difference = (1) - (2)
Estimate for difference: -0.750
95% CI for difference: (-1.943, 0.443)
T-Test of difference = 0 (vs ): T-Value = -1.45 P-Value = 0.185 DF = 8
Both use Pooled StDev = 0.8180

t = -1.45,    p-value = 0.185 > 0.05 , hence no

Well

Two-Sample T-Test and CI

Sample N    Mean StDev SE Mean
1       5 63.330 0.680     0.30
2       5 64.180 0.970     0.43

Difference = (1) - (2)
Estimate for difference: -0.850
95% CI for difference: (-2.072, 0.372)
T-Test of difference = 0 (vs ): T-Value = -1.60 P-Value = 0.147 DF = 8
Both use Pooled StDev = 0.8376

t = -1.60, p-value = 0.147 > 0.05

hence no

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