00 76.1/100 9/6/2016 o7:59 AM AM calculator Periodic Table earning ne the precis

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Question

00 76.1/100 9/6/2016 o7:59 AM AM calculator Periodic Table earning ne the precision and accuracy of these data for methylmercury. Sample 1 Sample 2 Sample 3 Known concentration: 25.2 ng/mL 74.0 ng/mL 215 ng/mL Experimentally 38.5 68.4 223 determined values 54,6 21.6 207 (ng/mL) 26.9 67.2 185 237 86,5 231 23,6 66.1 27.8 69.2 203 Sample 1 Precision Sample 2 Precision Deviation) Deviation) Sample 3 Precision (Rel Std Deviation) Number Sample 1 Accuracy Sample 2 Sample 3 Accuracy (Relative Error) (Relative Error) (Relative Error) Number Number Number Previous checks Answer Next

Explanation / Answer

Sample 1

Sample 2

Sample 3

Known concentration (xreal) (ng/mL)

25.2

74.0

215

Experimentally determined values (xi) (ng/mL)

36.5

68.4

223

21.6

54.6

207

26.9

67.2

185

23.7

86.5

231

23.6

66.1

177

27.8

69.2

203

Mean of experimentally determined values (xavg = xi/N, N = number of measurements) (ng/mL)

26.68

68.67

204.33

Precision, Rel. Standard deviation = (xi – xavg)2/N

4.863 (see sample calculation below)

9.354

19.102

Absolute error = xreal – xavg(the symbol denotes we are taking the absolute value without the sign)

1.48

5.33

10.67

Accuracy, Rel. error = (xreal – xavg)/xreal*100

5.87

7.20

4.96

(xi – xavg)2 = (36.5 – 26.68)2 + (21.6 – 26.68)2 + (26.9 – 26.68)2 + (23.7 – 26.68)2 + (23.6 – 26.68)2 + (27.8 – 26.68)2 = 141.9084

(xi – xavg)2/N = 23.6514

(xi – xavg)2/N = 4.863