CHEM 210 Final Exam Questions and Answers

CHEM 210 Final Exam Questions and Answers if the p-value is greater than 0.1, we generally conclude the data are consistent with the null hypothesis - Answer-true what is the best way to characterize the random error present in a measurement? - Answer-take replicate measurements of your analytes and using the standard deviation and a t-table specify an error bar with a confidence limit statistical interference assesses whether an observed phenomenon in the data can reasonably be attributed to chance or not - Answer-true suppose we collected a sample size n = 100 from some population and used the data to calculate a 95% confidence interval for the population mean. now suppose we are going to increase the sample size to n = 300. keeping all else constant, which of the following would we expect to occur as a result of increasing the sample size? - Answer-(1) the standard error would decrease, (2) the margin of error would decrease in designing a clinical trial where each subject receives both a placebo and a proposed treatment, what statistical test would be most appropriate? - Answer-paired t-test an atomic absorption analysis is to be done on the calcium in a sample of powdered milk. a 12.55 gram sample of the powder is wet ashed in nitric acid and diluted to 50.00 mL with distilled water. a 1.00 mL aliquot of this is transferred to a 50.00 mL solution using EDTA. using a wavelength of 422.6 nm in an atomic absorption experiment, this diluted sample showed an absorbance of 0.375. a standard calcium sample (treated the same way) with a known concentration of 20.0 ppm provided an absorbance of 0.859. what is the ppm of calcium in the powdered milk? - Answer-437 ppm in a 3 step serial dilution: the first dilution is 1/10, the second dilution is 1/5, and the third dilution is 1/4. what is the total dilution factor of this 3 step serial dilution procedure? - Answer-200 a solution was prepared by mixing 10.00 mL of unknown (X) with 5.00 mL of standard (S) containing 8.24 ug/mL and diluting the mixture to 50.0 mL. the measured signal areas from an atomic absorption spectrometer of X:S was 1.690:1.000. in a separate experiment in which the concentrations of X and S were equal, the measured signal areas of X:S was 0.930:1.000. the concentration of X in the unknown is? - Answer-7.49 ug/mL you set up a 10 tube Minimum Inhibitory Concentration test where the concentration of the antibiotic in each tube is a 1:2 dilution of the previous tube. if the concentration of the antibiotic tube 1 is 3200 ug/mL, what is the concentration of the antibiotic in tube 6? - Answer-100 ug/mL solution: (1/2)^5 x 3200 = 100 to measure the Ca in breakfast cereal, 0.561 g of crushed Cheerios was digested at 600*C in air for 2 hours. the residue was dissolved in 6 M HCl, quantitatively transferred to a volumetric flask and dilution to 100.0 mL. then 5.00-mL aliquots were transferred to 50.0-mL volumetric flasks. each was treated with standard Ca2+ ion solution (20.0 ppm), diluted to volume with H2O, and analyzed by flame atomic absorption. a graph was constructed from the readings. use this graph to determine the wt% Ca in Cheerios. - Answer-0.4%