Category Archives: Calculation

Kinetic Method for Manganese

Trace levels of manganese can be determined by measuring its catalytic effect on the oxidation of diethylamine by sodium periodate.  The rate of formation of the oxidation product is followed spectrophotometrically.  A series of external standards are prepared by adding … Continue reading

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Analysis of Anaerobic Sediments for Sulfides

A paper in the Journal of Chemical Education describes an experimental method for determining the concentrations of both insoluble metal sulfides, such as FeS2, and gaseous H2S in anaerobic sediments. Samples of sediment are placed in a flask along with … Continue reading

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Neocuproine Method: Analysis of Procedure

One method for determining copper is the “Neocuproine Method”. In this method, copper in a +1 oxidation state reacts with neocuproine (2,9-dimethyl-1,10-phenanthroline) to form a complex of Cu(neocuproine)2.  The complex is extracted into a chloroform-methanol mixture, giving a yellow solution … Continue reading

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Standards for the Spectrophotometric Analysis of Acetone

Suppose you need to prepare a set of calibration standards for the spectrophotometric analysis of acetone at a wavelength of 211 nm using a 1.00 cm cell. The molar absorptivity for acetone at this wavelength is 562. To maintain an … Continue reading

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Titrimetic Analysis of Mixtures

Shown below is a titration curve for a mixture of two monoprotic weak acids, HA and HB, where pKa,HA = 4.00 and pKa,HB = 8.00.  The titrant is 0.200 M NaOH. (a) Briefly explain how you can tell that this … Continue reading

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Sampling Plan for Cadmium Leeching from Strip Mine

One of the hazards of strip mining is that water passing through the mine’s “tailings” (the piles of discarded material) is often very acidic and contains high concentrations of metal ions, such as Pb2+ and Cd2+. (a) Suppose you are … Continue reading

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Extraction and Analysis of Gingko Leaves

You may know that there is a growing interest in the ginkgo tree because herbal supplements using extracts of ginkgo are believed to aid in fighting memory loss.  A recent paper [Lang, G.; Wai, C. M. Anal. Chem. 1999, 71, … Continue reading

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Developing a Sampling Plan for Lead in Soil

When leaded gasoline was available, automobiles were a significant source of the total yearly environmental emission of Pb.  During internal combustion lead in gasoline, which was present as tetraethyl lead, was vaporized.  The lead, now present as Pb0, adsorbed to … Continue reading

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Separating a Weakly Acidic Analyte from a Weakly Basic Interferent

Imagine  you have an aqueous sample containing a weak acid analyte, HA, and a weak base interferent, HI.  The following information about HA, HI, the method of analysis, and the sample are available to you: Ka,HA = 1.00 x 10-3 … Continue reading

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Sampling M & Ms

Carry out the following “experiment” to test the validity of the sampling constant equation mR2 = Ks where m is the sample’s mass, R is the relative standard deviation for sampling, and Ks is the sampling constant. Obtain a package … Continue reading

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