I need some help with these homework problems.Could you please show the work for
ID: 479670 • Letter: I
Question
I need some help with these homework problems.Could you please show the work for them. Thank You
(a) It is known from careful measurements that the concentration of magnesium in a material is 0.137 wt %. Your new analytical procedure gives you values of 0.129, 0.133, 0.136, 0.130, 0.128 and 0.131 wt %. Do your results differ from the expected result at the 95% confidence level?
(b) Samples of drinking water were analyzed for lead contamination. Analysis of the drinking water showed a lead concentration of 12.54 ppb. Analysis of a sample of the same drinking water spiked with 20.00 ppb lead gave a concentration of 29.63 ppb. Calculate the spike recovery. Is the method sufficiently accurate?
(c) A chemical technician wants to verify the precision of an analytical procedure used to determine citric acid concentration in orange juice. She obtains 10.00 mL of a particular orange juice and dilutes it to 100.00 mL with water. She then analyzes five aliquots of the solution with the following results:
Aliquot 1 12.33 mg/mL
Aliquot 2 12.59 mg/mL
Aliquot 3 11.89 mg/mL
Aliquot 4 12.11 mg/mL
Aliquot 5 11.71 mg/mL
What can you say about the precision based on these results? Should the method be certified?
Explanation / Answer
(a) It is known from careful measurements that the concentration of magnesium in a material is 0.137 wt %. Your new analytical procedure gives you values of 0.129, 0.133, 0.136, 0.130, 0.128 and 0.131 wt %. Do your results differ from the expected result at the 95% confidence level?
Mean = 0.13117
Std dev = 0.00293
Student’s t = 2.571
=0.1316 (2.571*0.002393)/6 =0.1316 + 1316
Mg is between 0.128 and 0.134 wt%
actual value (0.137) falls outside this range.
result is statistically different than the known value