Sapling Learning Determine the precision and accuracy of the

Sapling Learning Determine the precision and accuracy of these data for methylmercury. Sample 1 Sample 2 Sample 3 Known concentration: 24.2 ng/mL 75.5 ng/mL 239 ng/mL 69.9 56.1 68.7 88.0 67.6 70.7 245 231 209 255 201 227 Experimentally determined values: 35.5 20.6 25.9 22.7 22.6 26.8 (ng/mL) Sample 2 Precision (Rel Std Deviation) Sample 3 Precision Sample 1 Precision (Rel Std Deviation) Number Number Number 1 Accuracy Sample 2 Sample 2 Accuracy Relative Error) Number Sample 3 Accuracy Relative Error) Number Number % Previous Give Up & View Solution (2) Check Answer 0 Next Hint

Solution

Sample 1:

a) Calculation of precision or relative standard devitaion:

The average of the given measurements (x) = (x1 + x2 + x3 + x4 + x5 + x6)/6

i.e. x = (35.5+20.6+25.9+22.7+22.6+26.8)/6

x = 25.68

Now, the standard deviation (s) = [{(x1-x)² + (x2-x)² + (x3-x)² + (x4-x)² + (x5-x)² + (x6-x)²}/(N-1)]^1/2

i.e. s = [{(35.5-25.68)² + (20.6-25.68)² + (25.9-25.68)² + (22.7-25.68)² + (22.6-25.68)² + (26.8-25.68)²}/(6-1)]^1/2

s = 5.33

Now, the precision (relative standard deviation) = (s/x)*100

= 5.33/25.68

= 0.208

b) Calculation of accuracy (relative error):

The value of known concentration = 24.2 ng/mL

The average value of measurements = 25.68

Absolute error = 25.68 - 24.2 = 1.48 ng/mL

Now, the relative error = Absolute error/known concentration

= 1.48/24.2

= 0.06

Now, you can calculate the precision and accuracy for sample 2 and sample 3 easily by following the procedure shown above.

All the best!