Determination of Fat in a Snickers’ Bar
In a recent paper [J. Chem. Educ. 1997, 74, 1108-1111], Snow, Dunn and Patel describe the experimental determination of fat in a SnickersTM candy bar. The fat was removed by extraction with […]
Analytical Problem Exchange
Use the problems in this forum to jump-start your in-class exercises, out-of-class assignments, or use them in exams.
Calculating HCl Molarity and Titration Error
In determining the concentration of HCl by titrating against the primary weak base TRIS, the molarity of HCL is calculated using the following equation where GFW is the gram formula weight of […]
Indeterminate vs. Determinate Errors
Errors effecting analytical work are broadly classified as determinate or indeterminate. Briefly explain the difference between a determinate and an indeterminate error, citing at least three important ways which in they are […]
Comparison of Glucometers
A glucometer is a portable device used to monitor glucose levels in blood. Of concern for users is repeatability between units of the same model, or between different models. The following data […]
Spike Recovery for Analysis of Ginkgolide
One concern in any analysis is the impact of the sample’s matrix. A method for an analyte that is known to work well in one matrix may yield problems when applied to […]
Uncertainity in Dispensing a Reagent
Concentrated HCl is 37.2% w/w HCl (±0.5% w/w) and has a density of 1.19 g/mL (±0.01 g/mL). Suppose that you need to dispense 0.0500 mol of HCl with an uncertainty of no […]
Propagation of Error in Preparing Solutions
Suppose you have a bottle of 53.4% w/w NaOH (the density of which is 1.52 g/mL) from which you are to prepare a 1.000-L solution of 0.534 M NaOH. Two obvious ways to […]
Preparing Solutions
During lab you need to prepare a solution that is 5.00 x 10-2 M Fe(CN)63- using K3Fe(CN)6. (a) Explain how to make 500 mL of this solution so that you know its […]
Concentration of Parathion Solutions
Parathion, C10H16NO5PS, is a toxic organophosphorous pesticide. A recently published method [Sacks, et al. Anal. Chem. 2000, 72, 2055-2058] for parathion reports a detection limit of 10 ng/mL. Express this concentration in […]
Solubility of Milk of Magnesia
Milk of Magnesia, or MOM, is a suspension of Mg(OH)2. One method for determining the amount of Mg(OH)2 in MOM is to precipitate the Mg2+ as MgNH4PO4. Because this precipitate includes a […]
What is the Difference Between Repeatability, Reproducibility, Accuracy, and Precision?
In an editorial published in American Laboratory (November 2000), Ira S. Krull states that in “any science, then, one must present at the very outset evidence of repeatability, reproducibility, accuracy, and precision […]
Concentrations
Gratzel et. al. [Anal. Chem. 1999, 71, 2751-2756] describe the use of a diffusional microburet to transfer solutions to very small droplets of solvent. The purpose of their work is to run […]